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UniqueConstraint Class

.NET Framework (current version)
 

Represents a restriction on a set of columns in which all values must be unique.

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

System::Object
  System.Data::Constraint
    System.Data::UniqueConstraint

C#
C++
F#
VB
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public ref class UniqueConstraint : Constraint

NameDescription
System_CAPS_pubmethodUniqueConstraint(DataColumn^)

Initializes a new instance of the UniqueConstraint class with the specified DataColumn.

System_CAPS_pubmethodUniqueConstraint(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.

System_CAPS_pubmethodUniqueConstraint(array<DataColumn^>^)

Initializes a new instance of the UniqueConstraint class with the given array of DataColumn objects.

System_CAPS_pubmethodUniqueConstraint(array<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.

System_CAPS_pubmethodUniqueConstraint(String^, DataColumn^)

Initializes a new instance of the UniqueConstraint class with the specified name and DataColumn.

System_CAPS_pubmethodUniqueConstraint(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.

System_CAPS_pubmethodUniqueConstraint(String^, array<DataColumn^>^)

Initializes a new instance of the UniqueConstraint class with the specified name and array of DataColumn objects.

System_CAPS_pubmethodUniqueConstraint(String^, array<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.

System_CAPS_pubmethodUniqueConstraint(String^, array<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.

NameDescription
System_CAPS_protproperty_DataSet

This API supports the product infrastructure and is not intended to be used directly from your code. Gets the DataSet to which this constraint belongs.(Inherited from Constraint.)

System_CAPS_pubpropertyColumns

Gets the array of columns that this constraint affects.

System_CAPS_pubpropertyConstraintName

The name of a constraint in the ConstraintCollection.(Inherited from Constraint.)

System_CAPS_pubpropertyExtendedProperties

Gets the collection of user-defined constraint properties.(Inherited from Constraint.)

System_CAPS_pubpropertyIsPrimaryKey

Gets a value indicating whether or not the constraint is on a primary key.

System_CAPS_pubpropertyTable

Gets the table to which this constraint belongs.(Overrides Constraint::Table.)

NameDescription
System_CAPS_protmethodCheckStateForProperty()

This API supports the product infrastructure and is not intended to be used directly from your code. Gets the DataSet to which this constraint belongs.(Inherited from Constraint.)

System_CAPS_pubmethodEquals(Object^)

Compares this constraint to a second to determine if both are identical.(Overrides Object::Equals(Object^).)

System_CAPS_protmethodFinalize()

Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection.(Inherited from Object.)

System_CAPS_pubmethodGetHashCode()

Gets the hash code of this instance of the UniqueConstraint object.(Overrides Object::GetHashCode().)

System_CAPS_pubmethodGetType()

Gets the Type of the current instance.(Inherited from Object.)

System_CAPS_protmethodMemberwiseClone()

Creates a shallow copy of the current Object.(Inherited from Object.)

System_CAPS_protmethodSetDataSet(DataSet^)

Sets the constraint's DataSet.(Inherited from Constraint.)

System_CAPS_pubmethodToString()

Gets the ConstraintName, if there is one, as a string.(Inherited from Constraint.)

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.

The following example adds a UniqueConstraint to a DataSet and sets the EnforceConstraints property to true.

VB
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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

.NET Framework
Available since 1.1

This type is suitable for multithreaded read operations. You must synchronize any write operations.

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