DataTable.Constraints DataTable.Constraints DataTable.Constraints DataTable.Constraints Property

Definition

Gets the collection of constraints maintained by this table.

public:
 property System::Data::ConstraintCollection ^ Constraints { System::Data::ConstraintCollection ^ get(); };
[System.Data.DataSysDescription("DataTableConstraintsDescr")]
public System.Data.ConstraintCollection Constraints { get; }
member this.Constraints : System.Data.ConstraintCollection
Public ReadOnly Property Constraints As ConstraintCollection
Property Value

A ConstraintCollection that contains the collection of Constraint objects for the table. An empty collection is returned if no Constraint objects exist.

Examples

The following example adds a ForeignKeyConstraint to the collection of constraints.

private void CreateConstraint(DataSet dataSet, 
    string table1, string table2, string column1, string column2)
{
    ForeignKeyConstraint idKeyRestraint = new 
        ForeignKeyConstraint(dataSet.Tables[table1].Columns[column1],
        dataSet.Tables[table2].Columns[column2]);

    // Set null values when a value is deleted.
    idKeyRestraint.DeleteRule = Rule.SetNull;
    idKeyRestraint.UpdateRule = Rule.Cascade;

    // Set AcceptRejectRule to cascade changes.
    idKeyRestraint.AcceptRejectRule = AcceptRejectRule.Cascade;

    dataSet.Tables[table1].Constraints.Add(idKeyRestraint);
    dataSet.EnforceConstraints = true;
}
Private Sub CreateConstraint(dataSet As DataSet, _
    table1 As String, table2 As String, _
    column1 As String, column2 As String)

    Dim idKeyRestraint As ForeignKeyConstraint = _
        New ForeignKeyConstraint _
        (dataSet.Tables(table1).Columns(column1), _
        dataSet.Tables(table2).Columns(column2))

    ' Set null values when a value is deleted.
    idKeyRestraint.DeleteRule = Rule.SetNull
    idKeyRestraint.UpdateRule = Rule.Cascade

    ' Set AcceptRejectRule to cascade changes.
    idKeyRestraint.AcceptRejectRule = AcceptRejectRule.Cascade
    
    dataSet.Tables(table1).Constraints.Add(idKeyRestraint)
    dataSet.EnforceConstraints = True
End Sub

Remarks

A ForeignKeyConstraint restricts the action performed when a value in a column (or columns) is either deleted or updated. Such a constraint is intended to be used with primary key columns. In a parent/child relationship between two tables, deleting a value from the parent table can affect the child rows in one of the following ways.

  • The child rows can also be deleted (a cascading action).

  • The values in the child column (or columns) can be set to null values.

  • The values in the child column (or columns) can be set to default values.

  • An exception can be generated.

A UniqueConstraint becomes active when attempting to set a value in a primary key to a non-unique value.

Applies to