UniqueConstraint
Class
Definition
Represents a restriction on a set of columns in which all values must be unique.
public class UniqueConstraint : System.Data.Constraint
- Inheritance
Inherited Members
System.Data.Constraint
System.Object
Examples
The following example adds a UniqueConstraint to a DataSet and sets the EnforceConstraints property to true.
Public Sub CreateDataTable()
Dim dataTable As DataTable = New DataTable
dataTable.Columns.Add("CustomerID", Type.GetType("System.String"))
dataTable.Columns.Add("CompanyName", Type.GetType("System.String"))
Dim uniqueConstraint As UniqueConstraint = _
New UniqueConstraint("CustConstraint", _
New DataColumn() {dataTable.Columns("CustomerID"), _
dataTable.Columns("CompanyName")})
dataTable.Constraints.Add(uniqueConstraint)
End Sub
Remarks
The UniqueConstraint is enforced on a single column (or columns) to ensure that a primary key value is unique.
Constraints are not enforced unless the EnforceConstraints property is set to true.
When the a DataSet is merged with a second DataSet, constraints are not enforced until all merges are completed.
Constructors
| UniqueConstraint(DataColumn) |
Initializes a new instance of the UniqueConstraint class with the specified DataColumn. |
| UniqueConstraint(DataColumn[]) |
Initializes a new instance of the UniqueConstraint class with the given array of DataColumn objects. |
| UniqueConstraint(DataColumn, Boolean) |
Initializes a new instance of the UniqueConstraint class with the DataColumn to constrain, and a value specifying whether the constraint is a primary key. |
| UniqueConstraint(DataColumn[], Boolean) |
Initializes a new instance of the UniqueConstraint class with an array of DataColumn objects to constrain, and a value specifying whether the constraint is a primary key. |
| UniqueConstraint(String, DataColumn) |
Initializes a new instance of the UniqueConstraint class with the specified name and DataColumn. |
| UniqueConstraint(String, DataColumn[]) |
Initializes a new instance of the UniqueConstraint class with the specified name and array of DataColumn objects. |
| UniqueConstraint(String, DataColumn, Boolean) |
Initializes a new instance of the UniqueConstraint class with the specified name, the DataColumn to constrain, and a value specifying whether the constraint is a primary key. |
| UniqueConstraint(String, DataColumn[], Boolean) |
Initializes a new instance of the UniqueConstraint class with the specified name, an array of DataColumn objects to constrain, and a value specifying whether the constraint is a primary key. |
| UniqueConstraint(String, String[], Boolean) |
Initializes a new instance of the UniqueConstraint class with the specified name, an array of DataColumn objects to constrain, and a value specifying whether the constraint is a primary key. |
Properties
| Columns |
Gets the array of columns that this constraint affects. |
| IsPrimaryKey |
Gets a value indicating whether or not the constraint is on a primary key. |
| Table |
Gets the table to which this constraint belongs. |
Methods
| Equals(Object) |
Compares this constraint to a second to determine if both are identical. |
| GetHashCode() |
Gets the hash code of this instance of the UniqueConstraint object. |
Thread Safety
This type is suitable for multithreaded read operations. You must synchronize any write operations.