Database Access with RDO (Remote Data Objects)

 

Introduction to ODBC and RDO

 

Open Database Connectivity (ODBC) provides a set of application programming interface (API) functions which make it easier for a developer to connect to a wide range of database formats. ODBC gives the developer a method of designing programs that are not specific to database format whether you are using Oracle, SQL Server, Access, or others. ODBC drivers are DLLs that contain the functions that let you connect to various databases. Each ODBC driver is separate for each database format. ODBC drivers take the code from a program and convert the functions to the specific database format being used. RDO (Remote Data Objects) is a thin layer of code that acts as an ODBC "wrapper", enabling the developer to invoke ODBC functionality using familiar object method and property syntax.

 

The "Alphabet Soup" of Database Access

 

Prior to VB6 and the introduction of ADO (ActiveX Data Objects), VB programmers would generally use DAO (Data Access Objects) to interact with local databases such as MS Access and use RDO (Remote Data Objects) to interact with client/server databases such as Oracle and SQL Server. The concept behind ADO was Universal Data Access (UDA), where one database access method could be used for any data source; it was designed to replace both DAO and RDO. DAO remains a viable technology for interacting with MS Access databases as it is faster than ADO for that purpose; however, ADO is more flexible – using ADO, one could develop a prototype database application using MS Access in the back-end, and with a "flick of the wrist" (i.e., with very little coding changes) "upsize" that same application to use Oracle or SQL Server. As far as RDO is concerned, no new versions of it have been developed beyond the version that shipped with VB6, and there are no future plans for it.

 

In the VB4 and VB5 worlds, RDO was the main method used to interact with client/server databases. RDO works perfectly fine with VB6, so when folks migrated their VB5 applications over to VB6, little or no coding changes were required. However, ADO is the preferred method of database access for new VB6 applications .

 

About this Tutorial

 

This tutorial presents three small sample applications using RDO. All three applications use a local MS Access database, as this is suitable for illustrative purposes; in actual practice, RDO would not be a suitable choice for interacting with a local MS Access database. You could approach these sample applications "as if" the local Access database was an Oracle or SQL Server database sitting on a server somewhere – the coding techniques are the same.

 

The first sample application introduces the RDO Data Control (RDODC) which demonstrates a "quick and dirty" way to connect to a remote database. The second and third applications use RDO code: the second allows navigation and searching of a database table; the third allows navigation and updating on a database table. All three connect to an ODBC Data Source, which must be set up through the Windows Control Panel. How to do this is described below.

 

Setting Up an ODBC Data Source

 

Follow the steps below to set up an ODBC Data Source (this process is also called "setting up a DSN", where "DSN" stands for "Data Source Name"). These steps assume Windows 2000 for the operating system. On other versions of Windows, some steps may vary slightly.

 

·         Via Windows Control Panel, double-click on Administrative Tools, then Data Sources (ODBC). The ODBC Data Source Administrator screen is displayed, as shown below. Click on the System DSN tab.

 

 

·         Click the Add button. The Create New Data Source dialog box will appear. Select Microsoft Access Driver (*.mdb) from the list and click the Finish button.

 

 

·         The ODBC Microsoft Access Setup dialog box will appear. For Data Source Name, type Biblio. If desired, you can type an entry for Description, but this is not required.

 

 

·         Click the Select button. The Select Database dialog box appears. On a default installation of VB6 or Visual Studio 6, the BIBLIO.MDB sample database should reside in the folder C:\Program Files\Microsoft Visual Studio\VB98. Navigate to that folder, select BIBLIO.MDB from the file list, and click OK.

 

 

            Note: If VB was installed in a different location on your system, navigate to the appropriate folder. If you do not have the BIBLIO.MDB sample database file on your system at all, you can download it here. In that case, copy the file to the folder of your choice, and navigate to that folder to select the database for this step.

 

·         When you are returned to the ODBC Microsoft Access Setup screen, the database you selected should be reflected as shown below. Click OK to dismiss this screen.

 

 

·         When you are returned to the ODBC Data Source Administrator screen, the new DSN should appear as shown below. Click OK to dismiss this screen.

 

 

At this point, the Biblio database is ready to be used with RDO in the sample application.

 

Sample Application 1: Using the RDO Data Control (RDODC)

 

To build the first sample application, follow the steps below.

 

·         Start a new VB project, and from the Components dialog box (invoked from the Project -> Components menu), select Microsoft RemoteData Control 6.0 (SP3) as shown below and click OK.

 

            The RDO Data Control should appear in your toolbox as shown below:

 

 

·         Put a remote data control (RDC) on your form, and set the properties as follows:

 

Property

Value

Name

rdoBiblio

DataSourceName

Biblio

SQL

select * from authors

                               

·         Now put three text boxes on the form, and set their Name, DataSource, and DataField properties as follows:

 

Name

DataSource

DataField

txtAuthor

rdoBiblio

Author

txtAuID

rdoBiblio

Au_ID

txtYearBorn

rdoBiblio

Year Born

 

·         Save and run the program.  Notice how it works just like the other data control.

 

·         Now change the SQL property of the data control to select * from authors order by author and run the program again.  Notice the difference.

 

·         Change the SQL property back to what it was and add three command buttons to the form, and set their Name and Caption properties as follows:

 

Name

Caption

cmdNameOrder

Order by Name

cmdYearOrder

Order by Year

cmdIDOrder

Order by ID


 

·         Put the following code in the cmdNameOrder_Click event:

 

rdoBiblio.SQL = "select * from authors order by author"

rdoBiblio.Refresh

 

·         Put the following code in the cmdYearOrder_Click event:

 

rdoBiblio.SQL = "select * from authors order by [year born]"

rdoBiblio.Refresh

 

·         Put the following code in the cmdIDOrder_Click event:

 

rdoBiblio.SQL = "select * from authors order by au_id"

rdoBiblio.Refresh

 

·         Save and run the program and see what happens when you click the buttons.

 

A screen-shot of the sample app at run-time is shown below:

 

 

 

Download the project files for this sample application here.

 

 

Sample Applications 2 and 3: Using RDO Code

 

Sample applications 2 and 3 use a database called PROPERTY.MDB and can be downloaded here.

 

The Property database contains just one table called "Property". The columns of this table are defined as follows:

 

Column Name

Data Type

Notes

PROPNO

Number (Long Integer)

A number that uniquely identifies the property in the table. Should be treated as the Primary Key (although it is not defined as such in the sample database).

EMPNO

Number (Long Integer)

A number that identifies the real estate agent selling the property. In a real system, this would be the foreign key to the employee number in an Employee table (such a table is not present in the sample database).

ADDRESS

Text (20)

The street address of the property.

CITY

Text (15)

The city where the property is located.

STATE

Text (2)

The state where the property is located (2-character US state abbreviation).

ZIP

Text (5)

The zip code where the property is located.

NEIGHBORHOOD

Text (15)

The descriptive name of the neighborhood in which the property is located.

HOME_AGE

Number (Long Integer)

Age in years of the home. (A better table design choice would be to have this field be the date in which the property was built and have the application compute the age based on the current date.)

BEDS

Number (Long Integer)

Number of bedrooms in the property.

BATHS

Number (Single)

Number of bathrooms in the property (allows for a decimal value such as 2.5, indicating 2 ½ bathrooms – i.e. 2 full bathrooms and 1 "powder room").

FOOTAGE

Number (Long Integer)

The footage of the property.

ASKING

Number (Long Integer)

Asking price of the property in whole dollars.

BID

Number (Long Integer)

Bid amount of the potential buyer in whole dollars.

SALEPRICE

Number (Long Integer)

Sale price (amount the property actually sold for) in whole dollars.

 

Before coding or running sample application 2 or 3, you must set up an ODBC data source as was done for the previous sample application.

 

After downloading the file, move it to the folder of your choice. Then follow the exact same steps as before to set up the DSN, with these two exceptions:

 

(1)        On the ODBC Microsoft Access Setup dialog box, type PropDB for the Data Source Name.

 

(2)        In the Select Database dialog box, navigate to the location where you have placed the PROPERTY.MDB file.

 

Sample Application 2

 

To build Sample Application 2,  start a new VB project and perform the following steps.

 

·         From the Project -> References menu, check Microsoft Remote Data Object 2.0 and click OK.

 

 

·         This project uses the StatusBar control, so include the Microsoft Windows Common Controls 6.0 (SP6) from the Components dialog box, accessed from the Project -> Components menu.

 

 

·         Create the form shown below.  The names of the text boxes in the top frame are shown in the form. Set the Enabled property of the frame to False, which will automatically disable all of the textboxes within it, which is desired because this application does not allow updating of the data. The settings for the other controls are given below.

 

 

            The navigation buttons have the following properties:

 

Name

Caption

cmdMoveFirst

<<

cmdMovePrevious

<

cmdMoveNext

>

cmdMoveLast

>>

 

 

            The text box in the middle of the form has the following properties:

 

Name

txtCurrentQuery

MultiLine

True

Locked

True

 

            The command buttons have the following properties:

 

Name

Caption

cmdAllData

Reload All Records

cmdGetData

Run Query Now

 

            In the "Select Criteria" frame:

 

            The check boxes are an array:

Name

Caption

chkCriteria(0)    

EmpNo

chkCriteria(1)

City

chkCriteria(2)

State

 

            The labels are also an array:

Name

Caption

Enabled

lblCriteria(0)      

=

False

lblCriteria(1)

Like

False

lblCriteria(2)

Like

False

 

            The textboxes are also an array:

Name

Caption

Enabled

txtCriteria(0)     

EmpNo

False

txtCriteria(1)

City

False

txtCriteria(2)

State

False

 

            Place the StatusBar on the form and set its Style property to 1 – sbrSimple.

 

2.         Code the General Declarations section as shown below. Here, two RDO objects, rdoConnection and rdoResultset, are defined at the form level.

 

            The rdoConnection object represents an open connection to a remote data source and a specific database on that data source, or an allocated but as yet unconnected object, which can be used to subsequently establish a connection.

 

            The rdoResultset object represents the rows that result from running a query,

 

Option Explicit

 

Dim mobjRDOConn As rdoConnection

Dim mobjRDORst  As rdoResultset

Dim mstrSQL     As String

 

3.         Code the Form_Load event.  Here, the OpenConnection methods is introduced.

 

            OpenConnection is method of an existing rdoEnvironment object. An rdoEnvironment object defines a logical set of connections and transaction scope for a particular user name. rdoEnvironments(0) is a member of the rdoEnvironments collection and is created automatically when you include RDO in your program. The rdoEnvironments collection is one of several collections of the base RDO object, rdoEngine. The rdoEngine object is created automatically when you include RDO in your program.

           

            The syntax for the OpenConnection method is:

            Set connection = environment.OpenConnection(dsName[, prompt[, readonly[, connect[, options]]]])

            In this sample program, "PropDB" is used for the dsName argument, as this was the Data Source Name given during the ODBC setup.  The prompt argument controls whether or not the user is prompted for their UserID and password via the "ODBC Data Sources" dialog box. Provided that enough information is given within the other arguments of the OpenConnection method, the constant rdDriverNoPrompt will suppress the prompt. The third argument, readonly is a Boolean indicating whether or not the connection should be open for read/write access. The sample program omits this argument, thus defaulting to False, meaning the connection is open for read/write access. The connect argument is a string expression used to pass arguments to the ODBC driver manager for opening the database. In the case of the sample application, we are passing a user id of "admin" and a blank password in the connection string, which are the defaults for an unsecured MS Access database.

 

'-----------------------------------------------------------------------------

Private Sub Form_Load()

'-----------------------------------------------------------------------------

  

'set up the form and connect to the data source

On Error GoTo LocalError

  

    'center the form:

    Me.Top = (Screen.Height - Me.Height) / 2

    Me.Left = (Screen.Width - Me.Width) / 2

   

    ' Connect to the Property database:

    Set mobjRDOConn = rdoEngine.rdoEnvironments(0).OpenConnection _

            ("PropDB", rdDriverNoPrompt, , "UID=admin;PWD=")

 

    Call cmdAllData_Click

 

    Exit Sub

 

LocalError:

    MsgBox Err.Number & " - " & Err.Description

   

End Sub

 

4.         Code the cmdAllData_Click event, which sets or resets the Resultset object with a query to display all the rows in the table. Here, the OpenResultset method is introduced.

 

            The OpenResultset method causes an rdoResultset object to be created. The syntax is:

Set variable = connection.OpenResultset(name [,type [,locktype [,option]]])

            The name argument is a string that specifies the source of the rows for the new rdoResultset. This argument can specify the name of an rdoTable object, the name of an rdoQuery, or an SQL statement that might return rows. In the case of the sample application, it is the SQL statement "select * from property". The type argument specifies which type of cursor to create (using rdOpenKeyset allows the use of the "Move" methods (MoveFirst, MoveNext, etc.), so that option was coded here).  The locktype argument  specifies the concurrency option that controls how other users are granted or refused access to the data being updated. A value of rdConcurRowVer specifies optimistic concurrency based on row ID.

 

'-----------------------------------------------------------------------------

Private Sub cmdAllData_Click()

'-----------------------------------------------------------------------------

 

On Error GoTo LocalError

   

    Dim lngX    As Long

   

    'select or reload the data to be displayed:

    mstrSQL = "select * from property"

 

    Set mobjRDORst = mobjRDOConn.OpenResultset(mstrSQL, rdOpenKeyset, rdConcurRowVer)

    txtCurrentQuery.Text = mstrSQL

   

    'The number of records will be displayed in the status bar,

    'but the RowCount property is not correct until the last

    'record has been accessed (so do a MoveLast followed by a MoveFirst).

    mobjRDORst.MoveLast

    mobjRDORst.MoveFirst

   

    'load data into the text boxes

    Call DataLoad

   

    ' reset the state of the search criteria controls

    For lngX = 0 To 2

        chkCriteria(lngX).Value = vbUnchecked

    Next

   

    Exit Sub

   

LocalError:

    MsgBox Err.Number & " - " & Err.Description

 

End Sub

 

5.         Create the user-defined subprocedure DataLoad.  This subprocedure gets the data from the resultset and puts each field into a text box. Data from the resultset is accessed via the rdoColumns collection.

 

            The rdoColumns collection in RDO is similar to the Fields collection in DAO. A field can be referenced with or without specifying rdoColumns, either by the field name in quotes or by its ordinal position in the resultset. The field can also be referenced with the bang (!) operator.  All of the following would be valid ways of referencing the field "propno":

 

            mobjRDORst.rdoColumns("propno")

            mobjRDORst ("propno")

            mobjRDORst.rdoColumns(0)

            mobjRDORst(0)

            mobjRDORst!propno

 

'-----------------------------------------------------------------------------

Private Sub DataLoad()

'-----------------------------------------------------------------------------

On Error GoTo LocalError

 

    'copy the data from the resultset to the text boxes:

    txtPropNo.Text = mobjRDORst.rdoColumns("propno")

    txtEmpNo.Text = mobjRDORst.rdoColumns("empno")

    txtAddress.Text = mobjRDORst.rdoColumns("address")

    txtCity.Text = mobjRDORst.rdoColumns("city")

    txtState.Text = mobjRDORst.rdoColumns("state")

    txtZip.Text = mobjRDORst.rdoColumns("zip")

   

    Call SetRecNum

   

    Exit Sub

   

LocalError:

    MsgBox Err.Number & " - " & Err.Description

 

End Sub

 

6.         Create the user-defined subprocedure SetRecNum.  This sub displays the number of the current record at the bottom of the screen. The AbsolutePosition, RowCount, and PercentPosition properties of the Resultset are used here.

 

            The AbsolutePosition property specifies the current row in a resultset.

            The RowCount property specifies the number of rows in a resultset that have been accessed (the full count is only accurate after a "MoveLast" has been executed).

            The PercentPosition property indicates the location of the current resultset row based on a percentage.

 

'-----------------------------------------------------------------------------

Private Sub SetRecNum()

'-----------------------------------------------------------------------------

   

    StatusBar1.SimpleText = "row " & mobjRDORst.AbsolutePosition _

                          & " of " & mobjRDORst.RowCount _

                          & ", " & Format(mobjRDORst.PercentPosition, "#0.00") _

                          & "% of ResultSet"

           

End Sub

 

7.         Code the events for the navigation buttons as shown below, using the resultset "Move" methods to move to the first, last, next, or previous record, respectively.

'-----------------------------------------------------------------------------

Private Sub cmdMoveFirst_Click()

'-----------------------------------------------------------------------------

On Error GoTo LocalError

 

    mobjRDORst.MoveFirst

    Call DataLoad

    Exit Sub

   

LocalError:

    MsgBox Err.Number & " - " & Err.Description

   

End Sub

 

'-----------------------------------------------------------------------------

Private Sub cmdMoveLast_Click()

'-----------------------------------------------------------------------------

On Error GoTo LocalError

 

    mobjRDORst.MoveLast

    Call DataLoad

    Exit Sub

   

LocalError:

    MsgBox Err.Number & " - " & Err.Description

   

End Sub

 

'-----------------------------------------------------------------------------

Private Sub cmdMoveNext_Click()

'-----------------------------------------------------------------------------

On Error GoTo LocalError

 

    mobjRDORst.MoveNext

    If mobjRDORst.EOF Then

        Beep

        mobjRDORst.MoveLast

    End If

    Call DataLoad

    Exit Sub

   

LocalError:

    MsgBox Err.Number & " - " & Err.Description

   

End Sub

 

'-----------------------------------------------------------------------------

Private Sub cmdMovePrevious_Click()

'-----------------------------------------------------------------------------

On Error GoTo LocalError

 

    mobjRDORst.MovePrevious

    If mobjRDORst.BOF Then

        Beep

        mobjRDORst.MoveFirst

    End If

    Call DataLoad

    Exit Sub

   

LocalError:

    MsgBox Err.Number & " - " & Err.Description

   

End Sub

 

8.         When one of the check boxes is clicked, the label and text box next to it should be enabled (or disabled, if clicking the check box unchecks it). Note also that the cmdGetData button (the one with the "Run Query Now" caption) should only be enabled if one of the checkboxes is checked.

 

'-----------------------------------------------------------------------------

Private Sub chkCriteria_Click(Index As Integer)

'-----------------------------------------------------------------------------

 

    ' disable the 'Run Query Now' button

    cmdGetData.Enabled = False

 

    'when the user clicks on a check box, enable the label and text

    'box that go with it.

    If chkCriteria(Index).Value = vbChecked Then

        txtCriteria(Index).Enabled = True

        lblCriteria(Index).Enabled = True

        txtCriteria(Index).SetFocus

        txtCriteria(Index).SelStart = 0

        txtCriteria(Index).SelLength = Len(txtCriteria(Index).Text)

        ' enable the 'Run Query Now' button only if a box is checked.

        cmdGetData.Enabled = True

    Else

        txtCriteria(Index).Enabled = False

        lblCriteria(Index).Enabled = False

    End If

   

End Sub

 

9.         After the user has selected which fields to use and entered values in the text boxes, they click the cmdGetData button to create a new Resultset with new data. Note that if the user selects (checks) a field, but does not enter search criteria in the corresponding textbox, an error message is generated and the query is not run.

 

'-----------------------------------------------------------------------------

Private Sub cmdGetData_Click()

'-----------------------------------------------------------------------------

 

'run the query that the user has created

On Error GoTo LocalError

 

    Dim blnFirstOne As Boolean

    Dim i As Integer

   

    blnFirstOne = True

    mstrSQL = "select * from property where "

   

    If chkCriteria(0).Value = vbChecked Then

        If (txtCriteria(0).Text = "") Or (Not IsNumeric(txtCriteria(0).Text)) Then

            MsgBox "Employee number is missing or non-numeric. Query not run.", _

                   vbExclamation, _

                   "RDO Example"

            Exit Sub

        End If

        blnFirstOne = False

        mstrSQL = mstrSQL & "empno = " & txtCriteria(0).Text

    End If

   

    If chkCriteria(1).Value = vbChecked Then

        If txtCriteria(1).Text = "" Then

            MsgBox "City criteria is missing. Query not run.", _

                   vbExclamation, _

                   "RDO Example"

            Exit Sub

        End If

        If blnFirstOne = False Then

            mstrSQL = mstrSQL & " and"

        End If

        blnFirstOne = False

        mstrSQL = mstrSQL & " city like '" & txtCriteria(1).Text & "'"

    End If

   

    If chkCriteria(2).Value = vbChecked Then

        If txtCriteria(2).Text = "" Then

            MsgBox "State criteria is missing. Query not run.", _

                   vbExclamation, _

                   "RDO Example"

            Exit Sub

        End If

        If blnFirstOne = False Then

            mstrSQL = mstrSQL & " and"

        End If

        blnFirstOne = False

        mstrSQL = mstrSQL & " state like '" & txtCriteria(2).Text & "'"

    End If

       

    'create a new resultset using the new query

    Set mobjRDORst = mobjRDOConn.OpenResultset(mstrSQL, rdOpenKeyset, rdConcurRowVer)

    txtCurrentQuery.Text = mstrSQL

   

   

    'make sure that the query did not return 0 rows:

    If mobjRDORst.RowCount = 0 Then

        MsgBox "Your query returned 0 rows!"

        MsgBox "The query you generated was:" & vbCrLf & mstrSQL

        'reload the form with all the records

        cmdAllData_Click

    Else

       

        'move to last row to set the RowCount property

        mobjRDORst.MoveLast

        mobjRDORst.MoveFirst

   

        'load data into the text boxes

        Call DataLoad

   

        MsgBox "Your query returned " & mobjRDORst.RowCount & " records."

       

    End If

   

    Exit Sub

   

LocalError:

    MsgBox Err.Number & " - " & Err.Description

 

End Sub

 

 10.       Save and run. Note: When entering the "Like" criteria for City and/or State, you can use the wildcard character % to represent any number of characters and the wildcard character _ (underscore) the represent a single character. For example, entering "M%" for the City criteria would return all rows where the city field begins with the letter "M".

 

Download the project files for this sample application here.

 

Sample Application 3

 

Sample Application 3 demonstrates how to add, update, and delete records with RDO.

 

When the application is first run, the user is prompted to enter a minimum asking price to possibly limit the number of records they want to work with (i.e., "I only want to work with properties that are selling for $200,000 or more). If the user wants to work with all properties, they would simply accept the default of 0 from the prompt. If the user clicks the Cancel button, the application will end.

 

 

Once the user has entered the minimum asking price, the main screen of the application is displayed. Initially, the screen is in "browse" mode, where the user can use the navigation buttons to move to the first, previous, next or last record. The data cannot be edited in this mode. If they want to initiate an add or an update, delete a record, or exit the application, they may do so via the appropriate button. Saving or cancelling is not applicable in this mode, so those buttons are disabled.

 

 

If the user clicks the Add button, the fields on the screen are enabled and cleared, and the user can enter the information for the new property. All buttons except Save and Cancel are now disabled. After the user has made entries in the fields, he or she would click Save to add the new record to the database table, or, if they changed their mind, would click Cancel to discard the new record. In either case (clicking Save or Cancel) the user is returned to browse mode. When Save is clicked, the application validates the entries and will only save the record if all fields pass edit (otherwise, a message will appear indicating the problem entry and focus will be set to the problem field).

 

 

If the user clicks the Update button, the fields on the screen are enabled and the user can modify any or all of the fields (except for the Property Number, which is the primary key of the table). All buttons except Save and Cancel are now disabled. After the user has made modifications in the desired fields, he or she would click Save to update the record to the database table, or, if they changed their mind, would click Cancel to discard the changes. In either case (clicking Save or Cancel) the user is returned to browse mode. When Save is clicked, the application validates the entries and will only save the record if all fields pass edit (otherwise, a message will appear indicating the problem entry and focus will be set to the problem field).

 

 

If the user clicks the Delete button, the user is asked to confirm that they want to delete the current record. If they respond Yes, the record is deleted from the database table, and the main screen shows the next record in the table.

 

 

 

To build Sample Application 3,  start a new VB project and perform the following steps.

 

·         From the Project -> References menu, check Microsoft Remote Data Object 2.0 and click OK.

 

 

·         This project uses the StatusBar control, so include the Microsoft Windows Common Controls 6.0 (SP6) from the Components dialog box, accessed from the Project -> Components menu. Check this item and click OK.

 

 

 

·         Create the form shown below. The settings for the various controls are given below.

 

 

·         There are nine textboxes in the main frame of the form. The names and MaxLength settings for these are given below:

 

Name

Properties

txtPropNo

MaxLength: 5

txtEmpNo

MaxLength: 4

txtAddress

MaxLength: 20

txtCity

MaxLength: 15

txtState

MaxLength: 2

txtZip

MaxLength: 5

txtBeds

MaxLength: 1

txtBaths

MaxLength: 3 (allows fractional amount, like 1.5)

txtAsking

MaxLength: 0 (not specified)

 

·         Set up the Command Buttons as follows:

 

Name

Caption

cmdMoveFirst

<<

cmdMovePrevious

<

cmdMoveNext

>

cmdMoveLast

>>

cmdAdd

Add

cmdUpdate

Update

cmdDelete

Delete

cmdSave

Save

cmdCancel

Cancel

cmdExit

Exit

 

·         All controls on your form should have their TabIndex property set such that the tabbing order is correct.

 

·         Add a Module to the project, name it modCommon, and enter the code shown below. The code contains procedures described as follows:

 

CenterForm

Sub to center a form on the screen

ValidKey

Function to validate a keystroke for use in the KeyPress event of a textbox

ConvertUpper

Function to convert an alphabetic character entered in a textbox to uppercase, used in the KeyPress event of a textbox

SelectTextBoxText

Sub to highlight the text of a textbox when it receives focus. Used in the GotFocus event of a textbox.

TabToNextTextBox

Sub to "autotab" from one textbox to another when maximum number of characters that can be entered into the first textbox has been reached.

UnFormatNumber

Function to strip out non-numeric characters (dollar signs, commas, etc.) from a formatted number.

 

Option Explicit

 

Public Const gstrNUMERIC_DIGITS     As String = "0123456789"

Public Const gstrUPPER_ALPHA_PLUS   As String = "ABCDEFGHIJKLMNOPQRSTUVWXYZ,'-"

 

Public gblnPopulating               As Boolean

 

'------------------------------------------------------------------------

Public Sub CenterForm(pobjForm As Form)

'------------------------------------------------------------------------

 

    With pobjForm

        .Top = (Screen.Height - .Height) / 2

        .Left = (Screen.Width - .Width) / 2

    End With

 

End Sub

 

'------------------------------------------------------------------------

Public Function ValidKey(pintKeyValue As Integer, _

                         pstrSearchString As String) As Integer

'------------------------------------------------------------------------

 

'  Common function to filter out keyboard characters passed to this

'  function from KeyPress events.

'

'  Typical call:

'      KeyAscii = ValidKey(KeyAscii, gstrNUMERIC_DIGITS)

'

 

    If pintKeyValue < 32 _

    Or InStr(pstrSearchString, Chr$(pintKeyValue)) > 0 Then

        'Do nothing - i.e., accept the control character or any key

        '             in the search string passed to this function ...

    Else

        'cancel (do not accept) any other key ...

        pintKeyValue = 0

    End If

 

    ValidKey = pintKeyValue

 

End Function

 

'------------------------------------------------------------------------

Public Function ConvertUpper(pintKeyValue As Integer) As Integer

'------------------------------------------------------------------------

 

'  Common function to force alphabetic keyboard characters to uppercase

'  when called from the KeyPress event.

 

'  Typical call:

'      KeyAscii = ConvertUpper(KeyAscii)

'

 

    If Chr$(pintKeyValue) >= "a" And Chr$(pintKeyValue) <= "z" Then

        pintKeyValue = pintKeyValue - 32

    End If

 

    ConvertUpper = pintKeyValue

 

End Function

 

'-----------------------------------------------------------------------------

Public Sub SelectTextBoxText(pobjTextbox As TextBox)

'-----------------------------------------------------------------------------

 

    With pobjTextbox

        .SelStart = 0

        .SelLength = Len(.Text)

    End With

 

End Sub

 

'-----------------------------------------------------------------------------

Public Sub TabToNextTextBox(pobjTextBox1 As TextBox, pobjTextBox2 As TextBox)

'-----------------------------------------------------------------------------

 

    If gblnPopulating Then Exit Sub

   

    If pobjTextBox2.Enabled = False Then Exit Sub

   

    If Len(pobjTextBox1.Text) = pobjTextBox1.MaxLength Then

        pobjTextBox2.SetFocus

    End If

 

End Sub

 

'-----------------------------------------------------------------------------

Public Function UnFormatNumber(pstrNumberIn As String) As String

'-----------------------------------------------------------------------------

 

    Dim lngX            As Long

    Dim strCurrChar     As String

    Dim strNumberOut    As String

   

   

    strNumberOut = ""

    For lngX = 1 To Len(pstrNumberIn)

        strCurrChar = Mid$(pstrNumberIn, lngX, 1)

        If InStr("0123456789.", strCurrChar) > 0 Then

            strNumberOut = strNumberOut & strCurrChar

        End If

    Next

   

    UnFormatNumber = strNumberOut

 

End Function

 

·         Code the General Declarations section as shown below. Here, as in the previous sample application, two RDO objects, rdoConnection and rdoResultset, are defined at the form level, as are some other form-level variables that will be needed.

 

Option Explicit

 

Private mobjRDOConn         As rdoConnection

Private mobjRDORst          As rdoResultset

Private mstrSQL             As String

Private mdblMinAsking       As Double

Private mblnUpdatePending   As Boolean

Private mstrUpdateType      As String

 

Private mavntUSStates       As Variant

 

·         Code the Form_Load  event as shown below. In it, a programmer-defined Sub named GetMinimumAsking is called (that routine is the one that displays the initial prompt to the user to enter the minimum asking price of the properties they want to work with). Then, the variant array mavntUSStates is loaded with the 50 US state abbreviations, needed for validating the state input by the user. This is followed by a call to the CenterForm sub. Then, the RDO  OpenConnection is invoked so that we can use the Property database in the application. This is followed by a call to the programmer-defined Sub GetPropertyData (which runs the query to create the recordset that will be used to browse the Property table records), followed by a call to the programmer-defined Sub SetFormState (which enables and disables controls at the appropriate time).

 

'-----------------------------------------------------------------------------

Private Sub Form_Load()

'-----------------------------------------------------------------------------

  

    On Error GoTo LocalError

  

    ' obtain the minimum asking price for the properties to be worked with

    GetMinimumAsking

   

    ' load the array of states to be used for validation

    mavntUSStates = Array("AK", "AL", "AR", "AZ", "CA", "CO", "CT", "DC", _

                          "DE", "FL", "GA", "HI", "IA", "ID", "IL", "IN", _

                          "KS", "KY", "LA", "MA", "MD", "ME", "MI", "MN", _

                          "MO", "MS", "MT", "NC", "ND", "NE", "NH", "NJ", _

                          "NM", "NV", "NY", "OH", "OK", "OR", "PA", "RI", _

                          "SC", "SD", "TN", "TX", "UT", "VA", "VT", "WA", _

                          "WI", "WV", "WY")

                         

    'center the form:

    CenterForm Me

   

    ' Connect to the Property database:

    Set mobjRDOConn = rdoEngine.rdoEnvironments(0).OpenConnection _

            ("PropDB", rdDriverNoPrompt, , "UID=admin;PWD=")

 

    Call GetPropertyData

 

    SetFormState False

 

    Exit Sub

 

LocalError:

    MsgBox Err.Number & " - " & Err.Description

   

End Sub

 

Code the GetMinimumAsking Sub, which uses the InputBox function to prompt to the user to enter the minimum asking price of the properties they want to work with. The resulting value is then stored in the form-level variable mdblMinAsking.

 

'-----------------------------------------------------------------------------

Private Sub GetMinimumAsking()

'-----------------------------------------------------------------------------

   

    Dim strInputBoxPrompt   As String

    Dim strAsking           As String

 

    strInputBoxPrompt = "Enter the minimum asking price (for example, 200000) " _

                      & "for the properties that you want to work with this session." _

                      & vbNewLine _

                      & "To work with ALL properties, leave the default of zero."

    strAsking = InputBox(strInputBoxPrompt, "Minimum Asking Price", "0")

    If strAsking = "" Then

        ' user clicked Cancel button on the input box, so end the app

        End

    End If

    mdblMinAsking = Val(strAsking)

 

End Sub

 

Code the GetPropertyData Sub, which builds the SQL to get the property records meeting the minimum asking price condition. The OpenResultset method is then invoked to execute the SQL and return the resultset. This is done in a loop in case the resultset does not return any records due to the fact no records in the table met the asking price condition. In that situation, the user is given the opportunity to specify a different asking price value. Assuming we get to a point where we get records back, we do a MoveLast (to ensure a correct record count) followed by a MoveFirst to position to the first record in the resultset. Following this, the programmer-defined Sub PopulateFormFields is called (which displays the fields from the current record in their corresponding textboxes on the form).

 

'-----------------------------------------------------------------------------

Private Sub GetPropertyData()

'-----------------------------------------------------------------------------

 

    On Error GoTo LocalError

   

    Dim blnGotData  As Boolean

   

    blnGotData = False

   

    Do

        'select or reload the data to be displayed:

        mstrSQL = "select propno" _

                & "     , empno" _

                & "     , address" _

                & "     , city" _

                & "     , state" _

                & "     , zip" _

                & "     , beds" _

                & "     , baths" _

                & "     , asking" _

                & "  from property" _

                & " where asking >= " & mdblMinAsking _

                & " order by propno"

               

        Set mobjRDORst = mobjRDOConn.OpenResultset(mstrSQL, _

                                                   rdOpenKeyset, _

                                                   rdConcurRowVer)

       

        If mobjRDORst.EOF Then

            If MsgBox("There are no properties with an asking price >= " _

                    & Format$(mdblMinAsking, "Currency") _

                    & ". Do you want to try again with a different value?", _

                      vbYesNo + vbQuestion, _

                      "Asking Price") _

            = vbYes Then

                GetMinimumAsking

            Else

                End

            End If

        Else

            blnGotData = True

        End If

       

    Loop Until blnGotData

   

    'The number of records will be displayed in the status bar,

    'but the RowCount property is not correct until the last

    'record has been accessed (so do a MoveLast followed by a MoveFirst).

    mobjRDORst.MoveLast

    mobjRDORst.MoveFirst

   

    'load data into the text boxes

    Call PopulateFormFields

   

    Exit Sub

   

LocalError:

    MsgBox Err.Number & " - " & Err.Description

 

End Sub

 

Code the PopulateFormFields Sub, which assigns the fields from the current record to their corresponding textboxes on the form. Note that the gblnPopulating Boolean variable is set to True prior to the assignments and set to False after the assignments. This value is used to control whether or not certain code executes in the event procedures for some of these textboxes. The Sub SetRecNum is then called.

 

'-----------------------------------------------------------------------------

Private Sub PopulateFormFields()

'-----------------------------------------------------------------------------

   

    On Error GoTo LocalError

 

    gblnPopulating = True

 

    'copy the data from the resultset to the text boxes:

    txtPropNo.Text = mobjRDORst.rdoColumns("propno")

    txtEmpNo.Text = mobjRDORst.rdoColumns("empno")

    txtAddress.Text = mobjRDORst.rdoColumns("address")

    txtCity.Text = mobjRDORst.rdoColumns("city")

    txtState.Text = mobjRDORst.rdoColumns("state")

    txtZip.Text = mobjRDORst.rdoColumns("zip")

    txtBeds.Text = mobjRDORst.rdoColumns("beds")

    txtBaths.Text = mobjRDORst.rdoColumns("baths")

    txtAsking.Text = Format$(mobjRDORst.rdoColumns("asking"), "Currency")

   

    gblnPopulating = False

   

    Call SetRecNum

   

    Exit Sub

   

LocalError:

    MsgBox Err.Number & " - " & Err.Description

 

End Sub

 

Code the SetRecNum Sub.  This sub is identical to the one used in Sample Application 2. It displays the number of the current record at the bottom of the screen using the AbsolutePosition, RowCount, and PercentPosition properties of the Resultset object.

 

'-----------------------------------------------------------------------------

Private Sub SetRecNum()

'-----------------------------------------------------------------------------

   

    StatusBar1.SimpleText = "row " & mobjRDORst.AbsolutePosition _

                          & " of " & mobjRDORst.RowCount _

                          & ", " & Format(mobjRDORst.PercentPosition, "#0.00") _

                          & "% of ResultSet"

           

End Sub

 

Code the SetFormState Sub, which takes in a Boolean argument used to set the Enabled property of the controls on the form. Based on whether the value True or False is passed to this sub, this sub ensures that the textboxes are enabled for adds and updates and disabled for browsing; it also ensures that the various command buttons are enabled or disabled at the appropriate time. This Sub also sets the form-level Boolean variable mblnUpdatePending.

 

'-----------------------------------------------------------------------------

Private Sub SetFormState(pblnEnabled As Boolean)

'-----------------------------------------------------------------------------

 

    txtPropNo.Enabled = pblnEnabled

    txtEmpNo.Enabled = pblnEnabled

    txtAddress.Enabled = pblnEnabled

    txtCity.Enabled = pblnEnabled

    txtState.Enabled = pblnEnabled

    txtZip.Enabled = pblnEnabled

    txtBeds.Enabled = pblnEnabled

    txtBaths.Enabled = pblnEnabled

    txtAsking.Enabled = pblnEnabled

 

    cmdSave.Enabled = pblnEnabled

    cmdCancel.Enabled = pblnEnabled

       

    cmdAdd.Enabled = Not pblnEnabled

    cmdUpdate.Enabled = Not pblnEnabled

    cmdDelete.Enabled = Not pblnEnabled

    cmdExit.Enabled = Not pblnEnabled

   

    cmdMoveFirst.Enabled = Not pblnEnabled

    cmdMoveNext.Enabled = Not pblnEnabled

    cmdMovePrevious.Enabled = Not pblnEnabled

    cmdMoveLast.Enabled = Not pblnEnabled

   

    mblnUpdatePending = pblnEnabled

 

End Sub

 

Code the Form_Unload event. In it, the form-level Boolean variable mblnUpdatePending is tested to see if (well, an update is pending – i.e., whether an add or update is in progress). If the user is in the middle of an add or update and then clicks the "X" button on the upper-right corner of the form, they will receive the message that they must save or cancel prior to exiting the application, and the form will NOT be unloaded (because we are assigning a non-zero value to the Cancel argument in that situation). Provided that an add or update is not in progress, we set the database objects to Nothing and the Unload will complete.

 

'-----------------------------------------------------------------------------

Private Sub Form_Unload(Cancel As Integer)

'-----------------------------------------------------------------------------

 

    If mblnUpdatePending Then

        MsgBox "You must save or cancel the current operation prior to exiting.", _

               vbExclamation, _

               "Exit"

        Cancel = 1

    Else

        Set mobjRDORst = Nothing

        Set mobjRDOConn = Nothing

    End If

       

End Sub

 

Code the events for the various Textboxes as shown below. The code in these events ensure the following:

·         For all, highlight the text in the textbox when it receives focus.

·         For all but the last textbox, if the maximum number of characters typed into the textbox is reached, auto-tab to the next textbox.

·         Only numeric digits should be entered into the property number, employee number, zip codes, and beds textboxes.

·         Only numeric digits and optionally one decimal point should be entered into the baths and asking textboxes.

·         Force uppercase on the state textbox.

·         When the asking textbox receives focus, the value in there should be unformatted. When the asking textbox loses focus, its value should be formatted as currency.

 

'-----------------------------------------------------------------------------

'    Textbox events

'-----------------------------------------------------------------------------

 

' property #

Private Sub txtPropNo_GotFocus()

    SelectTextBoxText txtPropNo

End Sub

Private Sub txtPropNo_KeyPress(KeyAscii As Integer)

    KeyAscii = ValidKey(KeyAscii, gstrNUMERIC_DIGITS)

End Sub

Private Sub txtPropNo_Change()

    TabToNextTextBox txtPropNo, txtEmpNo

End Sub

 

' emp #

Private Sub txtEmpNo_GotFocus()

    SelectTextBoxText txtEmpNo

End Sub

Private Sub txtEmpNo_KeyPress(KeyAscii As Integer)

    KeyAscii = ValidKey(KeyAscii, gstrNUMERIC_DIGITS)

End Sub

Private Sub txtEmpNo_Change()

    TabToNextTextBox txtEmpNo, txtAddress

End Sub

 

' address

Private Sub txtAddress_GotFocus()

    SelectTextBoxText txtAddress

End Sub

Private Sub txtAddress_Change()

    TabToNextTextBox txtAddress, txtCity

End Sub

 

' city

Private Sub txtCity_GotFocus()

    SelectTextBoxText txtCity

End Sub

Private Sub txtCity_Change()

    TabToNextTextBox txtCity, txtState

End Sub

 

' state

Private Sub txtState_GotFocus()

    SelectTextBoxText txtState

End Sub

Private Sub txtState_KeyPress(KeyAscii As Integer)

    KeyAscii = ConvertUpper(KeyAscii)

End Sub

Private Sub txtState_Change()

    TabToNextTextBox txtState, txtZip

End Sub

 

' zip

Private Sub txtZip_GotFocus()

    SelectTextBoxText txtZip

End Sub

Private Sub txtZip_KeyPress(KeyAscii As Integer)

    KeyAscii = ValidKey(KeyAscii, gstrNUMERIC_DIGITS)

End Sub

Private Sub txtZip_Change()

    TabToNextTextBox txtZip, txtBeds

End Sub

 

' beds

Private Sub txtBeds_GotFocus()

    SelectTextBoxText txtBeds

End Sub

Private Sub txtBeds_KeyPress(KeyAscii As Integer)

    KeyAscii = ValidKey(KeyAscii, gstrNUMERIC_DIGITS)

End Sub

Private Sub txtBeds_Change()

    TabToNextTextBox txtBeds, txtBaths

End Sub

 

' baths

Private Sub txtBaths_GotFocus()

    SelectTextBoxText txtBaths

End Sub

Private Sub txtBaths_KeyPress(KeyAscii As Integer)

    KeyAscii = ValidKey(KeyAscii, gstrNUMERIC_DIGITS & ".")

    ' if text already has a decimal point, do not allow another ...

    If Chr$(KeyAscii) = "." And InStr(txtBaths.Text, ".") > 0 Then

        KeyAscii = 0

    End If

End Sub

Private Sub txtBaths_Change()

    TabToNextTextBox txtBaths, txtAsking

End Sub

 

' asking price

Private Sub txtAsking_GotFocus()

    txtAsking.Text = UnFormatNumber(txtAsking.Text)

    SelectTextBoxText txtAsking

End Sub

Private Sub txtAsking_KeyPress(KeyAscii As Integer)

    KeyAscii = ValidKey(KeyAscii, gstrNUMERIC_DIGITS & ".")

    ' if text already has a decimal point, do not allow another ...

    If Chr$(KeyAscii) = "." And InStr(txtAsking.Text, ".") > 0 Then

        KeyAscii = 0

    End If

End Sub

Private Sub txtAsking_LostFocus()

    txtAsking.Text = Format$(txtAsking.Text, "Currency")

End Sub

 

Code the events for the navigation buttons as shown below, using the resultset "Move" methods to move to the first, last, next, or previous record, respectively.

'-----------------------------------------------------------------------------

Private Sub cmdMoveFirst_Click()

'-----------------------------------------------------------------------------

   

    On Error GoTo LocalError

 

    mobjRDORst.MoveFirst

    Call PopulateFormFields

    Exit Sub

   

LocalError:

    MsgBox Err.Number & " - " & Err.Description

   

End Sub

 

'-----------------------------------------------------------------------------

Private Sub cmdMoveLast_Click()

'-----------------------------------------------------------------------------

   

    On Error GoTo LocalError

 

    mobjRDORst.MoveLast

    Call PopulateFormFields

    Exit Sub

   

LocalError:

    MsgBox Err.Number & " - " & Err.Description

   

End Sub

 

'-----------------------------------------------------------------------------

Private Sub cmdMoveNext_Click()

'-----------------------------------------------------------------------------

   

    On Error GoTo LocalError

 

    mobjRDORst.MoveNext

    If mobjRDORst.EOF Then

        Beep

        mobjRDORst.MoveLast

    End If

    Call PopulateFormFields

    Exit Sub

   

LocalError:

    MsgBox Err.Number & " - " & Err.Description

   

End Sub

 

'-----------------------------------------------------------------------------

Private Sub cmdMovePrevious_Click()

'-----------------------------------------------------------------------------

   

    On Error GoTo LocalError

 

    mobjRDORst.MovePrevious

    If mobjRDORst.BOF Then

        Beep

        mobjRDORst.MoveFirst

    End If

    Call PopulateFormFields

    Exit Sub

   

LocalError:

    MsgBox Err.Number & " - " & Err.Description

   

End Sub

 

Code the Click event for the cmdAdd button. In it, the textboxes are cleared, the SetFormState sub is called (passing it a parameter of True, which will enable the textboxes and the Save and Cancel buttons and disable all the other buttons), set the form-level variable mstrUpdateType to "A" (indicating that an add is pending) and sets focus to the Property Number field.

 

'-----------------------------------------------------------------------------

Private Sub cmdAdd_Click()

'-----------------------------------------------------------------------------

 

    On Error GoTo LocalError

 

    'clear all the text boxes:

    txtPropNo.Text = ""

    txtEmpNo.Text = ""

    txtAddress.Text = ""

    txtCity.Text = ""

    txtState.Text = ""

    txtZip.Text = ""

    txtBeds.Text = ""

    txtBaths.Text = ""

    txtAsking.Text = ""

   

    SetFormState True

    mstrUpdateType = "A"

    txtPropNo.SetFocus

   

    Exit Sub

   

LocalError:

    MsgBox Err.Number & " - " & Err.Description

   

End Sub

 

Code the Click event for the cmdUpdate button. In it, the SetFormState sub is called (passing it a parameter of True, which will enable the textboxes and the Save and Cancel buttons and disable all the other buttons), set the form-level variable mstrUpdateType to "U" (indicating that an update is pending), disables the Property Number field (because it is the primary key and should not be changed) and sets focus to the Employee Number field.

 

'-----------------------------------------------------------------------------

Private Sub cmdUpdate_Click()

'-----------------------------------------------------------------------------

 

    On Error GoTo LocalError

 

    SetFormState True

    mstrUpdateType = "U"

   

    ' being that propno is the primary key, it should not be updatable

    txtPropNo.Enabled = False

    txtEmpNo.SetFocus

   

    Exit Sub

   

LocalError:

    MsgBox Err.Number & " - " & Err.Description

   

End Sub

 

Code the Click event for the cmdSave button. The user would click this button after they have completed entries for an add or update. This sub first invokes the ValidateAllFields function, which returns a Boolean indicating whether or not all entries passed their edit checks. If not, we exit the sub and the record is not saved; the user remains in "update pending" mode and has the opportunity to correct the entries. Provided that validation is successful, the sub proceeds. The mstrUpdateType variable is checked to see whether we are dealing with an add or an update.

 

If we are dealing with an add, we invoke the AddNew method of the rdoResultset object (named mobjRDORst in this application). The AddNew method prepares a new row you can edit and subsequently add to the rdoResultset object using the Update method. After you modify the new row, you must use the Update method to save the changes and add the row to the result set. No changes are made to the database until you use the Update method. (The Update method is invoked after the content of the textboxes has been assigned to the database fields.)

If we are dealing with an update, we invoke the Edit method of the rdoResultset object (named mobjRDORst in this application). The Edit method enables changes to data values in the current row of an updatable rdoResultset object. Prior to invoking the Edit method, the data columns of an rdoResultset are read-only. Behind the scenes, executing the Edit method copies the current row from an updatable rdoResultset object to the copy buffer for subsequent editing. Changes made to the current row’s columns are copied to the copy buffer. After you make the desired changes to the row, use the Update method to save your changes or the CancelUpdate method to discard them. (If you move on to another record after invoking Edit but without invoking Update, your changes will be lost.)

Once the appropriate method has been invoked (either the AddNew or Edit), the content of the textboxes is assigned to the database fields, then the Update method is invoked. The Update method saves the contents of the copy buffer row to a specified updatable rdoResultset object and discards the copy buffer. (The Update method is the method that actually saves the data, and it must have been preceded by an AddNew or Edit.)

The mstrUpdateType variable is checked once again, and if we are dealing with an add, there is some extra work to do. Although the new record has been added, the original resultset still does not contain the new record. The Requery method must be invoked, which updates the data in an rdoResultset object by re-executing the query on which the object is based. Logic is then necessary to position to the new record. The SetRecNum sub must then be called to display the status bar information about the new record. Note: RDO does not have a Seek or FindFirst method, thus it is not possible to simply position a recordset to a particular row based on the value of a column. The workaround used by this sample application is to read rows sequentially (via the MoveNext method) until the desired row is found. This workaround is only practical for relatively small resultsets like the Property table – this would not be practical for a resultset containing thousands of rows.

In either case (add or update), the SetFormState sub is called with a parameter of False, which causes the textboxes and the Save and Cancel buttons to be disabled and all other buttons to be enabled.

Note that in the statement that assigns the contents of the txtAsking textbox to the asking field of the table, our UnFormatNumber function is used to strip off the non-numeric characters. This is because we are using a display format that includes a dollar sign and commas on the txtAsking control, and an error would occur if we attempted to assign this directly to the asking field, which is defined as numeric.

'-----------------------------------------------------------------------------

Private Sub cmdSave_Click()

'-----------------------------------------------------------------------------

 

    On Error GoTo LocalError

 

    If Not ValidateAllFields Then Exit Sub

 

    If mstrUpdateType = "A" Then

        mobjRDORst.AddNew

    Else

        mobjRDORst.Edit

    End If

   

    'save the data to the database:

    mobjRDORst.rdoColumns("propno") = txtPropNo.Text

    mobjRDORst.rdoColumns("empno") = txtEmpNo.Text

    mobjRDORst.rdoColumns("address") = txtAddress.Text

    mobjRDORst.rdoColumns("city") = txtCity.Text

    mobjRDORst.rdoColumns("state") = txtState.Text

    mobjRDORst.rdoColumns("zip") = txtZip.Text

    mobjRDORst.rdoColumns("beds") = txtBeds.Text

    mobjRDORst.rdoColumns("baths") = txtBaths.Text

    mobjRDORst.rdoColumns("asking") = UnFormatNumber(txtAsking.Text)

   

    mobjRDORst.Update

 

    If mstrUpdateType = "A" Then

        'after the new record is added, the db must be re-queried

        'so that the resultset contains the new record:

        mobjRDORst.Requery

        'since the number of records has changed, move to the

        'last record to reset the RowCount property:

        mobjRDORst.MoveLast

        mobjRDORst.MoveFirst

        ' reposition to the record just added

        Do Until mobjRDORst.EOF

            If mobjRDORst("propno") = Val(txtPropNo.Text) Then

                Exit Do

            End If

            mobjRDORst.MoveNext

        Loop

        'display status info about the new record

        SetRecNum

    End If

   

Reset:

    SetFormState False

   

    Exit Sub

   

LocalError:

    MsgBox Err.Number & " - " & Err.Description

   

    'if an error occured, the user should be instructed

    'how to fix it or the invalid data should be removed

    'from the text boxes and another record displayed

   

    Resume Reset

   

End Sub

 

Code the Click event for the cmdDelete button. The user is first asked to confirm that they want to delete the record, and if so, the Delete method of the resultset object (mobjRDORst) is invoked, which deletes the current row in an updatable resultset object. The Requery method is then invoked so that the record is removed from the resultset that the user is working with. Logic is then needed to position to a different record (either the next record after the deleted one, or, if it was the last record that was deleted, the record that preceded the deleted record). PopulateFormFields must then be called to display the contents of the new current record.

 

'-----------------------------------------------------------------------------

Private Sub cmdDelete_Click()

'-----------------------------------------------------------------------------

 

    On Error GoTo LocalError

   

    'when the current record is deleted, the current location in the recordset

    'is invalid.  use the Requery method to re-execute the query and update

    'the data.

   

    If MsgBox("Are you sure you want to delete this record?", _

              vbYesNo + vbQuestion, _

              "Delete") = vbNo Then

        Exit Sub

    End If

   

    mobjRDORst.Delete

    mobjRDORst.Requery

   

    'since the number of records has changed, move to the last record to

    'reset the RowCount property:

    mobjRDORst.MoveLast

    mobjRDORst.MoveFirst

   

    ' reposition to one past the record just deleted

    Do Until mobjRDORst.EOF

        If mobjRDORst("propno") > Val(txtPropNo.Text) Then

            Exit Do

        End If

        mobjRDORst.MoveNext

    Loop

    ' If it was the last record that was deleted, this will position us

    ' to the "new" last record ...

    If mobjRDORst.EOF Then mobjRDORst.MoveLast

   

    'load data into the text boxes:

    Call PopulateFormFields

 

    Exit Sub

 

LocalError:

    MsgBox Err.Number & " - " & Err.Description

   

End Sub

 

The ValidateAllFields function, which returns a Boolean value indicating whether or not all fields have passed validation checks. This function calls upon two "helper" functions: PropertyExists and ValidState.  When the user is doing an add, the PropertyExist function is called to see whether or not the proposed Property Number is already being used in the Property table. If so, the user is informed that they can't use that number (because it is the primary key and must be unique) and so they must use a different number. The ValidState routine is called to ensure that the user has entered a valid US state. The code for all three functions is shown below.

 

'-----------------------------------------------------------------------------

Private Function ValidateAllFields() As Boolean

'-----------------------------------------------------------------------------

 

    ValidateAllFields = False       'guilty until proven innocent

   

    If mstrUpdateType = "A" Then

        If txtPropNo.Text = "" Then

            MsgBox "Property # must not be blank.", vbExclamation, "Property #"

            txtPropNo.SetFocus

            Exit Function

        ElseIf PropertyExists Then

            MsgBox "Property # already exists. Please use a different #.", _

                   vbExclamation, _

                   "Property #"

            txtPropNo.SetFocus

            Exit Function

        End If

    End If

       

    If txtEmpNo.Text = "" Then

        MsgBox "Emp # must not be blank.", vbExclamation, "Emp #"

        txtEmpNo.SetFocus

        Exit Function

    End If

   

    If txtAddress.Text = "" Then

        MsgBox "Address must not be blank.", vbExclamation, "Address"

        txtAddress.SetFocus

        Exit Function

    End If

   

    If txtCity.Text = "" Then

        MsgBox "City must not be blank.", vbExclamation, "City"

        txtCity.SetFocus

        Exit Function

    End If

   

    If Not ValidState Then

        MsgBox "Missing or invalid state.", vbExclamation, "State"

        txtState.SetFocus

        Exit Function

    End If

   

    If txtZip.Text = "" Or Len(txtZip.Text) = 5 Then

        ' it's OK

    Else

        MsgBox "Zip code must either be blank or exactly 5 digits.", vbExclamation, "Zip Code"

        txtZip.SetFocus

        Exit Function

    End If

   

    If Val(txtBeds.Text) = 0 Then

        MsgBox "Beds must not be zero.", vbExclamation, "Beds"

        txtBeds.SetFocus

        Exit Function

    End If

   

    If Val(txtBaths.Text) = 0 Then

        MsgBox "Baths must not be zero.", vbExclamation, "Baths"

        txtBaths.SetFocus

        Exit Function

    End If

   

    If Val(UnFormatNumber(txtAsking.Text)) = 0 Then

        MsgBox "Asking must not be zero.", vbExclamation, "Asking"

        txtAsking.SetFocus

        Exit Function

    End If

   

    ' if we make it here, all fields have passed edit

    ValidateAllFields = True

   

End Function

 

'-----------------------------------------------------------------------------

Private Function PropertyExists() As Boolean

'-----------------------------------------------------------------------------

 

    Dim objTempRst  As rdoResultset

    Dim strSQL      As String

 

    strSQL = "select count(*) as the_count from property where propno = " & txtPropNo.Text

    Set objTempRst = mobjRDOConn.OpenResultset(strSQL, _

                                               rdOpenKeyset, _

                                               rdConcurRowVer)

    If objTempRst("the_count") > 0 Then

        PropertyExists = True

    Else

        PropertyExists = False

    End If

 

End Function

 

'--------------------------------------------------------------------------------

Private Function ValidState() As Boolean

'--------------------------------------------------------------------------------

 

    Dim lngX            As Long

    Dim blnStateFound   As Boolean

   

    blnStateFound = False

   

    For lngX = 0 To UBound(mavntUSStates)

        If txtState.Text = mavntUSStates(lngX) Then

            blnStateFound = True

            Exit For

        End If

    Next

   

    ValidState = blnStateFound

   

End Function

Code the Click event for the cmdCancel button. The user would click this button if, during an add or update, they decide to abandon the operation. Here, PopulateFormFields is called to reset the textboxes to their content prior to the user clicking the Add or Update button, and SetFormState is called with a parameter of False, which causes the textboxes and the Save and Cancel buttons to be disabled and all other buttons to be enabled.

'-----------------------------------------------------------------------------

Private Sub cmdCancel_Click()

'-----------------------------------------------------------------------------

 

    PopulateFormFields

    SetFormState False

   

End Sub

Code the Click event for the cmdExit button, which issues the Unload Me statement to fire the Form_Unload event, which will unload the form and end the application.

 

'-----------------------------------------------------------------------------

Private Sub cmdExit_Click()

'-----------------------------------------------------------------------------

 

    Unload Me

   

End Sub

 

 

Download the project files for this sample application here.

 

The Execute Method

The Execute method of the RDO Connection object can be used to run an action query or execute an SQL statement that does not return rows. Such queries include UPDATE, INSERT, and DELETE statements.

In the cmdSave_Click procedure, the following code segment:

   If mstrUpdateType = "A" Then

        mobjRDORst.AddNew

    Else

        mobjRDORst.Edit

    End If

   

    'save the data to the database:

    mobjRDORst.rdoColumns("propno") = txtPropNo.Text

    mobjRDORst.rdoColumns("empno") = txtEmpNo.Text

    mobjRDORst.rdoColumns("address") = txtAddress.Text

    mobjRDORst.rdoColumns("city") = txtCity.Text

    mobjRDORst.rdoColumns("state") = txtState.Text

    mobjRDORst.rdoColumns("zip") = txtZip.Text

    mobjRDORst.rdoColumns("beds") = txtBeds.Text

    mobjRDORst.rdoColumns("baths") = txtBaths.Text

    mobjRDORst.rdoColumns("asking") = UnFormatNumber(txtAsking.Text)

   

    mobjRDORst.Update

could be replaced by:

If mstrUpdateType = "A" Then

    mobjRDOConn.Execute "INSERT INTO property(  propno " _

                            & "               , empno" _

                            & "               , address" _

                            & "               , city" _

                            & "               , state" _

                            & "               , zip" _

                            & "               , beds" _

                            & "               , baths" _

                            & "               , asking" _

                            & ") VALUES (" _

                            & "   " & txtPropNo.Text _

                            & ",  " & txtEmpNo.Text _

                            & ", '" & Replace$(txtAddress.Text, "'", "''") & "'" _

                            & ", '" & Replace$(txtCity.Text, "'", "''") & "'" _

                            & ", '" & txtState.Text & "'" _

                            & ", '" & txtZip.Text & "'" _

                            & ",  " & txtBeds.Text _

                            & ",  " & txtBaths.Text _

                            & ",  " & UnFormatNumber(txtAsking.Text) _

                            & ")"

Else

    mobjRDOConn.Execute "UPDATE property " _

                      & "   SET empno   =  " & txtEmpNo.Text _

                      & "     , address = '" & Replace$(txtAddress.Text, "'", "''") & "'" _

                      & "     , city    = '" & Replace$(txtCity.Text, "'", "''") & "'" _

                      & "     , state   = '" & txtState.Text & "'" _

                      & "     , zip     = '" & txtZip.Text & "'" _

                      & "     , beds    = '" & txtBeds.Text & "'" _

                      & "     , baths   = '" & txtBaths.Text & "'" _

                      & "     , asking  = '" & UnFormatNumber(txtAsking.Text) & "'" _

                      & " WHERE propno  =  " & txtPropNo.Text

End If

Note 1:              Note that the portion of the code above that executes the SQL UPDATE statement includes a WHERE clause which insures that only the row for the current property number is updated. Recall from the SQL tutorial that an UPDATE statement should always have a WHERE clause to explicitly limit the row(s) to be updated. Without a WHERE clause, ALL rows of the table would be updated.

Note 2:              As pointed out in the DAO tutorials, for text fields, if there is the possibility that the value to be updated or inserted will contain an apostrophe, an extra measure should be taken to "double" the apostrophes when building the SQL string – otherwise, the apostrophe embedded in the string will be interpreted as the premature ending of the SQL string and a syntax error will most likely result. The easiest way to provide this "insurance" against embedded apostrophes is to use the Replace$ function on the string in question to replace any occurrences of a single apostrophe with two apostrophes.

In the cmdDelete_Click procedure, the following statement:

    mobjRDORst.Delete

could be replaced by:

mobjRDOConn.Execute "DELETE FROM property WHERE propno = " & txtPropNo.Text

Recall from the SQL tutorial that, like an UPDATE staement,  a DELETE statement should always have a WHERE clause to explicitly limit the row(s) to be deleted. Without a WHERE clause, ALL rows of the table would be deleted.