ConstraintCollection.Add Method (Constraint)

Adds the specified Constraint object to the collection.

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

public void Add (
	Constraint constraint
public void Add (
	Constraint constraint
public function Add (
	constraint : Constraint
Not applicable.



The Constraint to add.

Return Value

A new UniqueConstraint or ForeignKeyConstraint.

Exception typeCondition


The constraint argument is null.


The constraint already belongs to this collection, or belongs to another collection.


The collection already has a constraint with the same name. (The comparison is not case-sensitive.)

If the collection is successfully changed by adding or removing constraints, the CollectionChanged event occurs.

The following example adds a UniqueConstraint to the ConstraintCollection of a DataTable.

private void AddConstraint(DataTable table)
    UniqueConstraint uniqueConstraint;
    // Assuming a column named "UniqueColumn" exists, and 
    // its Unique property is true.
    uniqueConstraint = new UniqueConstraint(

Windows 98, Windows Server 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

XNA Framework

Supported in: 1.0