How To Manufacture an ADO Recordset Based on Another Recordset

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Some corporate policies allow read-only access to database tables with all updates being performed through stored procedures. If you want to bind a data control, such as the Microsoft Data Grid or List View control, to an ADO recordset, this can pose a problem keeping the recordset in sync with the data if you can allow adding, deleting, and modifying records but you cannot edit it directly through the recordset.

More Information

If you want to keep a recordset in sync with the server but you cannot add records through the hierarchical recordset, there are a number of workarounds:
  1. You can requery the recordset. This has the disadvantage of poor performance.
  2. You can disconnect the recordset and perform additions and other modifications in parallel with stored procedures. The problem here is that certain fields are read-only, such as Identity and TimeStamp, and you cannot set their value. This becomes problematic if the Identity column is supplied to the stored procedures to identify the record to be updated, or if the TimeStamp column is passed to the stored procedure to determine if someone else has edited the record in the meantime. There are a number of workarounds:
    1. You can copy the data to a local database, such as a Jet MDB, and use datatypes that do not make the field read-only. You can then update the recordset in parallel to using stored procedures and keep the data in sync.
    2. You can manufacture a recordset based on the original and copy the data into it. The fields are all updatable and you can update the recordset in parallel to using stored procedures.
This article provides sample code for the second workaround. It is generic enough to work with any non-hierarchical recordset (Chapter fields are not copied). If you need to use hierarchical recordsets, please refer to the following Microsoft Knowledge Base article:
241202 How To Produce a Manufactured Hierarchical Recordset Base on an Existing Recordset
This article provides the following functions:

Function NameDescription
MakeRSCreates a closed, empty Recordset with fields with the same names and data types as the original. Chaptered fields are not copied.
OpenAndFillRSOpens the destination Recordset and copies data from the (already open) source Recordset. Data in Chaptered fields are not copied.

The sample application has the following steps:
  1. It opens a recordset.
  2. It calls MakeRS to create an equivalent recordset that is not based on any provider and hence does not have any read-only fields.
  3. It calls OpenAndFillRS to open the recordset and copy the data from the original recordset.
  4. It closes the original recordset.
  5. It binds the ADO Data Grid to the manufactured recordset.
NOTE: The code does not provide samples of updating the server table and making equivalent changes to the manufactured recordset. This is left as an exercise for the reader because the manufactured recordset is now in a state to make this possible.

Sample Application

  1. Open a new project in Microsoft Visual Basic 6.0. Form1 is created by default.
  2. From the Projects menu, choose Components, select the "Microsoft DataGrid Control 6.0 (OLEDB)" control, and place it on the form. Make it fairly large.
  3. From the Projects menu, choose References, select "Microsoft ActiveX Data Objects 2.1 Library."
  4. Add the following code to the form module:
    Option Explicit

    Private Sub Command1_Click()
    Dim cn As ADODB.Connection, rsSource As ADODB.Recordset, rsDest As ADODB.Recordset
    Set cn = New ADODB.Connection
    cn.Open "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=nwind.mdb"
    Set rsSource = cn.Execute("SELECT * FROM Customers")
    Set rsDest = MakeRS(rsSource)
    OpenAndFillRS rsSource, rsDest
    Set DataGrid1.DataSource = rsDest
    End Sub

    Function MakeRS(ByVal rsSource As ADODB.Recordset) As ADODB.Recordset
    Dim rsTemp As ADODB.Recordset, F As ADODB.Field
    Set rsTemp = New ADODB.Recordset
    For Each F In rsSource.Fields
    If F.Type <> adChapter Then
    rsTemp.Fields.Append F.Name, F.Type, F.DefinedSize, F.Attributes And adFldIsNullable
    With rsTemp(F.Name)
    .Precision = F.Precision
    .NumericScale = F.NumericScale
    End With
    End If
    Next F
    Set MakeRS = rsTemp
    End Function

    Sub OpenAndFillRS(ByVal rsSource As ADODB.Recordset, ByVal rsDest As ADODB.Recordset)
    Dim F As ADODB.Field
    If rsSource.State = adStateClosed Then Exit Sub<BR/>
    If rsSource.EOF And rsSource.BOF Then Exit Sub
    If rsSource.CursorType <> adOpenForwardOnly Then
    If Not rsSource.EOF And Not rsSource.BOF Then
    End If
    End If
    rsDest.CursorLocation = adUseClient

    Do While Not rsSource.EOF
    For Each F In rsSource.Fields
    If F.Type <> adChapter Then rsDest(F.Name).Value = F.Value
    Next F
    End Sub
  5. Add a CommandButton, modify the connect string in the Command1_Click procedure, and run the project. The customer's data is displayed in the grid after you click the CommandButton.


For additional information, click the following article number to view the article in the Microsoft Knowledge Base:
305346 How To Copy DataRows Between DataTables by Using Visual Basic .NET

ID članka: 247868 - posljednja izmjena: 2. srp 2004. - verzija: 1

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