Private Sub ShowConstraints(ByVal tableName As String)

    Dim table As DataTable = New DataTable(tableName)
    Using connection As sqlConnection = New sqlConnection(GetConnectionString)

        Dim adapter As sqlDataAdapter = New sqlDataAdapter("Select top 1 * from " + _                  
                                                  tableName,connection)
        connection.Open()
        adapter.FillSchema(table,SchemaType.Mapped)

        For Each c As Constraint In table.Constraints
            If TypeOf c Is ForeignKeyConstraint Then
                Dim fk As ForeignKeyConstraint = CType(c,ForeignKeyConstraint)
                Console.WriteLine("** FK ** relatedTable: {0}; RelatedColumns: {1}",_
                    fk.RelatedTable,fk.RelatedColumns)
            Else
                Console.WriteLine("** Whatever ** Name: {0}; Type: {1}",_
                                           c.ConstraintName,c.GetType.ToString)
            End If
        Next

    End Using


End Sub

我怎样才能获得ForeignKey约束？