UniqueConstraint Class
Definition
Important
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Represents a restriction on a set of columns in which all values must be unique.
public ref class UniqueConstraint : System::Data::Constraint
public class UniqueConstraint : System.Data.Constraint
[System.Serializable]
public class UniqueConstraint : System.Data.Constraint
type UniqueConstraint = class
inherit Constraint
[<System.Serializable>]
type UniqueConstraint = class
inherit Constraint
Public Class UniqueConstraint
Inherits Constraint
- Inheritance
- Attributes
Examples
The following example adds a UniqueConstraint to a DataSet and sets the EnforceConstraints property to true
.
Public Sub CreateDataTable()
Dim dataTable As 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, 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[]) |
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 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, 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[]) |
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, 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
_DataSet |
Gets the DataSet to which this constraint belongs. (Inherited from Constraint) |
Columns |
Gets the array of columns that this constraint affects. |
ConstraintName |
The name of a constraint in the ConstraintCollection. (Inherited from Constraint) |
ExtendedProperties |
Gets the collection of user-defined constraint properties. (Inherited from Constraint) |
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
CheckStateForProperty() |
Gets the DataSet to which this constraint belongs. (Inherited from Constraint) |
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. |
GetType() |
Gets the Type of the current instance. (Inherited from Object) |
MemberwiseClone() |
Creates a shallow copy of the current Object. (Inherited from Object) |
SetDataSet(DataSet) |
Sets the constraint's DataSet. (Inherited from Constraint) |
ToString() |
Gets the ConstraintName, if there is one, as a string. (Inherited from Constraint) |
Applies to
Thread Safety
This type is suitable for multithreaded read operations. You must synchronize any write operations.