DataTable.Constraints Property

Definition

Namespace:

System.Data

Assemblies:

netstandard.dll, System.Data.Common.dll

Source:

DataTable.cs

Gets the collection of constraints maintained by this table.

C#

public System.Data.ConstraintCollection Constraints { get; }

Property Value

ConstraintCollection

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.

C#

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;
}

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

See also

• DataTables