Microsoft KB Archive/168313

= ACC97: DAO Property Retrieval Slow with Linked Table Objects =

Article ID: 168313

Article Last Modified on 1/19/2007

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APPLIES TO


 * Microsoft Access 97 Standard Edition

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This article was previously published under Q168313



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



SYMPTOMS
When you use Data Access Objects (DAO) to retrieve properties for linked TableDef objects, the process is much slower than when you use DAO to retrieve the properties for local TableDef objects.

This article assumes that you are familiar with Visual Basic for Applications and with creating Microsoft Access applications using the programming tools provided with Microsoft Access. For more information about Visual Basic for Applications, please refer to the "Building Applications with Microsoft Access 97" manual.



CAUSE
The Microsoft Jet database engine must create a temporary query for each property retrieval of a linked TableDef object. The Jet database engine does not need to do this when retrieving properties for local TableDef objects.



RESOLUTION
Instead of retrieving the properties for the linked TableDef objects in the current database, you can use DAO to open the database that the TableDef objects actually reside in, and then retrieve the properties. To accomplish this, follow steps 1 through 17 in the "Steps to Reproduce Behavior" section later in this article and substitute the following procedure for the procedure documented in step 15: Sub EnumProperties(tDefName As String) Dim db As Database Dim tDef As TableDef Dim tDefSourceTableName As String Dim tDefProperty As Property Dim PropCount As Integer Dim dbPath As String Dim tDefField As Field Dim StartTime As Date, EndTime As Date

StartTime = Now Set db = CurrentDb Set tDef = db.TableDefs(tDefName)

If (tDef.Attributes And dbAttachedTable) <> 0 Then If InStr(tDef.Connect, ".mdb") > 0 Then tDefSourceTableName = tDef.SourceTableName dbPath = Right$(tDef.Connect, _                       Len(tDef.Connect) - _                        InStr(tDef.Connect, "=")) Set db = DBEngine(0).OpenDatabase(dbPath) Set tDef = db.TableDefs(tDefSourceTableName) End If      End If

For Each tDefProperty In tDef.Properties Next

For Each tDefField In tDef.Fields For Each tDefProperty In tDefField.Properties PropCount = PropCount + 1 Next Next

EndTime = Now Debug.Print Debug.Print "Table: " & tDef.Name Debug.Print "Number of Table and Field Properties: " & _ tDef.Properties.Count + PropCount Debug.Print "Total Time: " & _ DateDiff("s", StartTime, EndTime) & " second(s)" db.Close

End Sub



STATUS
This behavior is by design.



Steps to Reproduce Behavior
CAUTION: Following the steps in this example will modify the sample database Northwind.mdb. You may want to back up the Northwind.mdb file and perform these steps on a copy of the database.  Open the sample database Northwind.mdb.  Create a module and type the following line in the Declarations section if it is not already there: Option Explicit   Type the following procedure. This procedure adds 700 user-defined properties to the Employees table. Sub CreateProperties Dim db As Database Dim tDef As TableDef Dim prop As Property Dim i As Integer

Set db = CurrentDb Set tDef = db.TableDefs!Employees For i = 1 To 700 Set prop = tDef.CreateProperty("Prop" & i, dbText, i)            tDef.Properties.Append prop Next tDef.Properties.Refresh MsgBox "Number of Properties: " & tDef.Properties.Count db.Close End Sub  To run this procedure, type the following line in the Debug window, and then press ENTER.

CreateProperties

Note that the message box indicates the number of properties that were added to the Employees table. This number will include any existing properties as well. Create a new, blank database named PropTest.mdb.</li> On the File menu, point to Get External Data, and then click Import.</li> In the Import dialog box, select Microsoft Access (*.mdb) from the Files Of Type list.</li> Locate your Office97\Office\Samples folder, select Northwind.mdb, and then click Import.</li> In the Import Objects dialog box, select the Employees table, and then click OK.</li> On the File menu, point to Get External Data, and then click Link Tables.</li> In the Link dialog box, select Microsoft Access (*.mdb) from the Files Of Type list.</li> Locate your Samples folder, select Northwind.mdb, and then click Link.</li> In the Link Tables dialog box, select the Employees table, and then click OK. Note that the linked table is named "Employees1."</li>  Create a module and type the following line in the Declarations section if it is not already there: Option Explicit </li>  Type the following procedure: Sub EnumProperties(tDefName As String) Dim db As Database Dim tDef As TableDef Dim tDefProperty As Property Dim PropCount As Integer Dim tDefField As Field Dim StartTime As Date, EndTime As Date

StartTime = Now Set db = CurrentDb Set tDef = db.TableDefs(tDefName) For Each tDefProperty In tDef.Properties Next

For Each tDefField In tDef.Fields For Each tDefProperty In tDefField.Properties PropCount = PropCount + 1 Next Next

EndTime = Now Debug.Print Debug.Print "Table: " & tDef.Name Debug.Print "Number of Table and Field Properties: " & _ tDef.Properties.Count + PropCount Debug.Print "Total Time: " & _ DateDiff("s", StartTime, EndTime) & " second(s)" db.Close End Sub </li> Test this procedure with the local Employees table to determine the amount of time it takes to enumerate its properties. To run this procedure, type the following line in the Debug window, and then press ENTER.

EnumProperties "Employees"

Note the number of seconds it takes to enumerate through all properties of the Employees table.</li> Test this procedure with the linked Employees1 table to determine the amount of time it takes to enumerate its properties. To run this procedure, type the following line in the Debug window, and then press ENTER.

EnumProperties "Employees1"

Note that the number of seconds it takes to enumerate the properties of the linked table is much higher.</li></ol>

Keywords: kbprb kbprogramming KB168313

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