IndexedAttribute Class

Indicates that a property or field affects index creation.

Assembly : DevExpress.Xpo.v25.2.dll

Declaration

C#
VB.NET

csharp

[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field, Inherited = true)]
public sealed class IndexedAttribute :
    Attribute

<AttributeUsage(AttributeTargets.Property Or AttributeTargets.Field, Inherited:=True)>
Public NotInheritable Class IndexedAttribute
    Inherits Attribute

Remarks

The IndexedAttribute attribute indicates that a table (or another data store) should have an index for the column(s). An index allows a database to find data in a table without scanning the entire table. Indexes can be created for a single property (column) or combination of properties (columns). For more information on multi-column (compound) indexes, refer to the IndexedAttribute.AdditionalFields property description.

Note

XPO does not support tables with multi-column (compound) keys or indexes in ASE databases. To avoid exceptions when connecting to ASE databases containing these tables, use one-column keys or indexes.

For instance, you can apply the IndexedAttribute attribute to a persistent property to make it unique (see the example below):

C#
VB.NET

csharp

public class User : XPObject {
    [Indexed(Unique = true)]
    public int UserId {
        get { return fUserId; }
        set { SetPropertyValue(nameof(UserId), ref fUserId, value); }
    }
    int fUserId;

    public string UserName {
        get { return fUserName; }
        set { SetPropertyValue(nameof(UserName), ref fUserName, value); }
    }
    string fUserName;
}

Public Class User
    Inherits XPObject

    <Indexed(Unique:=True)>
    Public Property UserId As Integer
        Get
            Return fUserId
        End Get
        Set(ByVal value As Integer)
            SetPropertyValue(NameOf(UserId), fUserId, value)
        End Set
    End Property

    Private fUserId As Integer

    Public Property UserName As String
        Get
            Return fUserName
        End Get
        Set(ByVal value As String)
            SetPropertyValue(NameOf(UserName), fUserName, value)
        End Set
    End Property

    Private fUserName As String
End Class

This index ensures that the UserId value is unique for all database records (both existing and deleted objects). To avoid a unique constraint violation when a deleted and existing object have the same UserId value, include the GCRecord field in the index. For more information, refer to the following help section: Include XPO’s Service Columns into Indexes to Enable Unique Value Constraints.

To define several non-unique database indices, use IndicesAttribute.

Inheritance

Object Attribute IndexedAttribute