Programming Visual Basic .NET

Relations Between DataTables in a DataSet

The DataSet class provides a mechanism for specifying relations between tables in a DataSet. The DataSet class’s Relations property contains a RelationsCollection object, which maintains a collection of DataRelation objects. Each DataRelation object represents a parent/child relationship between two tables in the DataSet. For example, there is conceptually a parent/child relationship between a Customers table and an Orders table, because each order must belong to some customer. Modeling this relationship in the DataSet has these benefits:

• The DataSet can enforce relational integrity.

• The DataSet can propagate key updates and row deletions.

• Data-bound controls can provide a visual representation of the relation.

Example 8-4 loads a Customers table and an Orders table from the Northwind database and then creates a relation between them. The statement that actually creates the relation is shown in bold.

Example 8-4. Creating a DataRelation between DataTables in a DataSet

' Open a database connection. Dim strConnection As String = _ "Data Source=localhost;Initial Catalog=Northwind;" _ & "Integrated Security=True" Dim cn As SqlConnection = New SqlConnection(strConnection) cn.Open( ) ' Set up a data adapter object. Dim strSql As String = "SELECT * FROM Customers" _ & " WHERE City = 'Buenos Aires' AND Country = 'Argentina'" Dim da As SqlDataAdapter = New SqlDataAdapter(strSql, cn) ' Load a data set. Dim ds As DataSet = New DataSet( ) da.Fill(ds, ...