Microsoft KB Archive/210127

= ACC2000: Creating Functions Similar to DFirst and DLast =

Article ID: 210127

Article Last Modified on 6/23/2005

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APPLIES TO


 * Microsoft Access 2000 Standard Edition

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This article was previously published under Q210127



Advanced: Requires expert coding, interoperability, and multiuser skills.

This article applies only to a Microsoft Access database (.mdb).



SUMMARY
By design, the DFirst and DLast functions always return the first and last record that you entered in the underlying table, not the first and last record as ordered by the table's index or the query's sort order. DFirst and DLast ignore indexes, even primary keys and sort orders.

This article shows you how to write custom domain functions that you can use in a way similar to DFirst and DLast. The DStart and DEnd custom domain examples in this article return the first and last records listed in a sorted query.

Microsoft provides programming examples for illustration only, without warranty either expressed or implied. This includes, but is not limited to, the implied warranties of merchantability or fitness for a particular purpose. This article assumes that you are familiar with the programming language that is being demonstrated and with the tools that are used to create and to debug procedures. Microsoft support engineers can help explain the functionality of a particular procedure, but they will not modify these examples to provide added functionality or construct procedures to meet your specific requirements.



MORE INFORMATION
CAUTION: If you follow the steps in this example, you modify the sample database Northwind.mdb. You may want to back up the Northwind.mdb file and follow these steps on a copy of the database.

To create and use custom domain functions similar to DFirst and Dlast, follow these steps:  Open the sample database Northwind.mdb.  Create a new module and enter the following two functions: '-- ' Use DStartinstead of DFirst to return ' the first sorted record in a domain. '-- Function DStart(FieldName As String, DomainName As String, Optional _ Criteria As Variant)

Dim MyDB As DATABASE, MySet As Recordset

' Error out if there is no fieldname sent. If Len(FieldName) = 0 Then MsgBox "You Must Specify a Field name",, "DStart" Exit Function End If

' Error out if there is no domain sent. If Len(DomainName) = 0 Then MsgBox "You Must Specify a Domain name",, "DStart" Exit Function End If

Set MyDB = CurrentDb Set MySet = MyDB.OpenRecordset(DomainName, dbOpenDynaset)

' Apply a filter to the recordset if a criteria is sent. If Not IsMissing(Criteria) Then MySet.Filter = Criteria Set MySet = MySet.OpenRecordset End If

' If there are no records, return the null, else return the value ' of the first record. If MySet.EOF Then DStart = Null Else MySet.MoveFirst DStart = MySet(FieldName) End If

MySet.Close MyDB.Close End Function

'--- 'Use DEndinstead of DLast to return ' the last sorted record in a domain. '---

Function DEnd(FieldName As String, DomainName As String, Optional _ Criteria As Variant)

Dim MyDB As DATABASE, MySet As Recordset

' Error out if there is no fieldname sent. If Len(FieldName) = 0 Then MsgBox "You Must Specify a Field name",, "DEnd" Exit Function End If

' Error out if there is no domainname sent. If Len(DomainName) = 0 Then MsgBox "You Must Specify a Domain name",, "DEnd" Exit Function End If

Set MyDB = CurrentDb Set MySet = MyDB.OpenRecordset(DomainName, dbOpenDynaset)

' Apply a filter to the recordset if a criteria is sent. If Not IsMissing(Criteria) Then MySet.Filter = Criteria Set MySet = MySet.OpenRecordset End If

' If there are no records, return the null, else return the value ' of the last record. If MySet.EOF Then DEnd = Null Else MySet.MoveLast DEnd = MySet(FieldName) End If MySet.Close MyDB.Close End Function

 Close and save the new module.  Create a new query based on the Orders table as follows:   Query: Orders By Date -  Type: Select Query

Field: OrderID Table: Orders Field: OrderDate Table: Orders Sort: Descending  Close and save the query as RecentOrders.  Open the Immediate window, type the following expression, and then press ENTER: ?DStart("OrderID","RecentOrders") Note that the OrderID 11077 is returned, which is the first OrderID in the query. </li>  Type the following expression in the Immediate window, and then press ENTER: ?DFirst("OrderID","RecentOrders") Note that the OrderID 10314 (or 10248 in 7.0) is returned, which is the first OrderID entered in the Orders table, not the first in the RecentOrders query. </li></ol>

General Limitations to Custom Domain Functions
You cannot use Forms!FormName!ControlName or Form.ID in quotation marks. For example, instead of

DStart("[ProductName]","Products","[ProductID]=Forms![Products]![ProductID]")

use:

DStart("[ProductName]","Products", BuildCriteria("[ProductID]",dblong,"=" & Forms![Products]![ProductID]))

Note that the BuildCriteria function is a Visual Basic function that creates a properly formed criteria string. You can use BuildCriteria anywhere you concatenate criteria strings, such as the FindFirst method or when building custom SQL criteria.

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