Creating a Data Relation Object in Code

In Chapter 21, the ParentChildData example used the publishers and titles tables in the pubs database and related them through the pub_id key. This example displayed the publishers.pub_name field in the combo box you see in Figure 21.12, and when the user selected a publisher, the program displayed all that publisher's books in the datagrid below. In that chapter, we created a data relation object visually, but now we'll see how to do the same thing by creating a DataRelation object in code, as shown in the ParentChildDataCode example on the CD-ROM.

To create the new DataRelation object, I just pass this object's constructor the name of the new object, the parent column, and the child column. Then I add the new relation object to a dataset's Relations collection, and bind a data grid to that object, like this:

Private Sub Form1_Load(ByVal sender As System.Object, _
        ByVal e As System.EventArgs) Handles MyBase.Load
    DataSet11.Clear()
    OleDbDataAdapter1.Fill(DataSet11)
    OleDbDataAdapter2.Fill(DataSet11)

    Dim PublishersColumn As DataColumn
    Dim TitlesColumn As DataColumn

    PublishersColumn = DataSet11.Tables("publishers").Columns("pub_id")
    TitlesColumn = DataSet11.Tables("titles").Columns("pub_id")

    Dim publisherstitles As DataRelation
    publisherstitles = New DataRelation("publisherstitles", _
        PublishersColumn, TitlesColumn)

    DataSet11.Relations.Add(publisherstitles)
    DataGrid1.SetDataBinding(DataSet11, "publishers.publisherstitles")
End Sub

This creates the same master/detail connection that the ParentChildData example gave us in Chapter 21. You can see this example, ParentChildDataCode, at work in Figure 22.6 (compare it to Figure 21.12).

Figure 22.6: Using a data relation object.