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DataTable.Constraints Property
System.Data Namespace DataTable Class
Returns the collection of constraints maintained by this table.
Syntax
| Script | [ ConstraintCollection variable = ] DataTable.Constraints |
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Property Value
| variable | Returns a ConstraintCollection that contains the collection of Constraint objects for the table; otherwise a null value if no Constraint objects exist. |
The property is read only with no default value.
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.
Example
The following example adds a ForeignKeyConstraint to the collection of constraints.
Private void ConstraintsDemo ( DataSet myDataSet, string table1,
string table2, string column1, string column2 ) {
ForeignKeyConstraint idKey = new ForeignKeyConstraint
( myDataSet.Tables [ Table1 ].Columns [ Column1 ],
myDataSet.Tables [ Table2 ].Columns [ Column2 ] );
// set null values when a value is deleted.
idKey.DeleteRule = Rule.SetNull;
idKey.UpdateRule = Rule.Cascade;
// set AcceptRejectRule to cascade changes.
idKey.AcceptRejectRule = AcceptRejectRule.Cascade;
myDataSet.Tables [ Table1 ].Constraints.Add ( idKey );
myDataSet.EnforceConstraints = true;
}
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| C# | VB | |
See Also
DataTable Members AcceptRejectRule ForeignKeyConstraint UniqueConstraint Rule
