IndexedAttribute Class

Indicates that a property or field participates in index creation.

Namespace: DevExpress.Xpo

Assembly: DevExpress.Xpo.v21.1.dll

NuGet Package: DevExpress.Xpo

Declaration

C#

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

VB.NET

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

Remarks

The IndexedAttribute attribute indicates that a table (or another form of data store) will 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 on either a single property (column) or a 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#

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;

}

VB.NET

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

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

Inheritance

Object

Attribute

IndexedAttribute