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
UniqueConstraint

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.