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, ...
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