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DataTable.Constraints Property


Gets the collection of constraints maintained by this table.

Namespace:   System.Data
Assembly:  System.Data (in System.Data.dll)

public ConstraintCollection Constraints { get; }

Property Value

Type: System.Data.ConstraintCollection

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

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.

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 

    // 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.EnforceConstraints = true;

.NET Framework
Available since 1.1
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