KeyAttribute Class

Indicates that a property or a field is a key.

Namespace: DevExpress.Xpo

Assembly: DevExpress.Xpo.v21.1.dll

Declaration

C#

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

VB.NET

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

Remarks

Apply this attribute to a property or a field to mark it as a key. The KeyAttribute.AutoGenerate property specifies whether the key is generated automatically.

You can change key property values for new unsaved objects only. If you change a key property for a saved object, the identity map may not function correctly. Define a key property as “read-only” whenever possible:

C#

[Key(true), Persistent("CategoryID")]
int fCategoryID = -1;

[PersistentAlias(nameof(fCategoryID))]
public int CategoryID {
    get { return fCategoryID; }
}

VB.NET

<Key(True), Persistent("CategoryID")> _
Private fCategoryID As Integer = -1

<PersistentAlias(NameOf(fCategoryID))> _
Public ReadOnly Property CategoryID() As Integer
    Get
        Return fCategoryID
    End Get
End Property

Related GitHub Examples

The following code snippets (auto-collected from DevExpress Examples) contain references to the KeyAttribute class.

Note

The algorithm used to collect these code examples remains a work in progress. Accordingly, the links and snippets below may produce inaccurate results. If you encounter an issue with code examples below, please use the feedback form on this page to report the issue.

C#

XPO_how-to-create-persistent-classes-mapped-to-tables-with-a-composite-primary-key-at-runtime-e4606/CS/XpoConsoleApplication/Program.cs#L16

XPClassInfo ciEngineer = dict.CreateClass("Engineer");
ciEngineer.CreateMember("UserID", typeof(string), new KeyAttribute(), new SizeAttribute(8));
ciEngineer.CreateMember("PublicName", typeof(string), new SizeAttribute(32));

XPO_how-to-create-an-xpclassinfo-descendant-to-dynamically-build-a-persistent-class-structure-e1729/CS/DynamicDataTable/DynamicDataTableClassInfo.cs#L22

    if (table.PrimaryKey[0] == column)
        member.AddAttribute(new KeyAttribute(column.AutoIncrement));
}

XPO_how-to-generate-persistent-metadata-for-an-arbitrary-data-table-e2922/CS/MapArbitraryDatabaseExample/Program.cs#L41

classInfo.CreateMember(table.PrimaryKey.Columns[0], DBColumn.GetType(primaryColumnType),
    new KeyAttribute(IsAutoGenerationSupported(primaryColumnType)));
foreach (DBColumn col in table.Columns)

XPO_how-to-generate-persistent-classes-at-runtime-based-on-a-dataset-e1198/CS/WindowsApplication4/Form1.cs#L31

    if (key == c.Name)
        mi.AddAttribute(new KeyAttribute(c.IsIdentity));
}

XPO_how-to-define-a-persistent-class-at-runtime-e1139/CS/CreateClassAtRuntime/Program.cs#L18

XPClassInfo myClassA = dictionary.CreateClass(myBaseClass, "MyObjectA");
myClassA.CreateMember("ID", typeof(int), new KeyAttribute(true));
myClassA.CreateMember("Name", typeof(string));

VB.NET

XPO_how-to-create-persistent-classes-mapped-to-tables-with-a-composite-primary-key-at-runtime-e4606/VB/XpoConsoleApplication/Program.vb#L16

Dim ciEngineer As XPClassInfo = dict.CreateClass("Engineer")
ciEngineer.CreateMember("UserID", GetType(String), New KeyAttribute(), New SizeAttribute(8))
ciEngineer.CreateMember("PublicName", GetType(String), New SizeAttribute(32))

XPO_how-to-create-an-xpclassinfo-descendant-to-dynamically-build-a-persistent-class-structure-e1729/VB/DynamicDataTable/DynamicDataTableClassInfo.vb#L26

If table.PrimaryKey(0) Is column Then
    member.AddAttribute(New KeyAttribute(column.AutoIncrement))
End If

XPO_how-to-generate-persistent-metadata-for-an-arbitrary-data-table-e2922/VB/MapArbitraryDatabaseExample/Program.vb#L41

Dim primaryColumnType As DBColumnType = table.GetColumn(table.PrimaryKey.Columns(0)).ColumnType
classInfo.CreateMember(table.PrimaryKey.Columns(0), DBColumn.GetType(primaryColumnType), New KeyAttribute(IsAutoGenerationSupported(primaryColumnType)))
For Each col As DBColumn In table.Columns

XPO_how-to-generate-persistent-classes-at-runtime-based-on-a-dataset-e1198/VB/WindowsApplication4/Form1.vb#L29

If key = c.Name Then
    mi.AddAttribute(New KeyAttribute(c.IsIdentity))
End If

XPO_how-to-define-a-persistent-class-at-runtime-e1139/VB/CreateClassAtRuntime/Program.vb#L18

Dim myClassA As XPClassInfo = dictionary.CreateClass(myBaseClass, "MyObjectA")
myClassA.CreateMember("ID", GetType(Integer), New KeyAttribute(True))
myClassA.CreateMember("Name", GetType(String))

Inheritance

Object

Attribute

KeyAttribute