ExplicitLoadingAttribute Class

Specifies that the information used to retrieve persistent objects that are referenced by the current property, is included in a query used to load this property.

Namespace: DevExpress.Xpo

Assembly: DevExpress.Xpo.v19.2.dll

Declaration

C#

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

VB.NET

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

C#

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

VB.NET

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

Remarks

By design, when a property referencing a persistent object is loaded, XPO generates and executes several queries to retrieve this property. One retrieves a reference to the persistent object and the other for each property of the persistent object. It is a recursive process, since the retrieved property in its turn might reference another persistent object. To improve performance by assembling the intermediate queries into one query which is executed only once, use the ExplicitLoadingAttribute. The reference depth of the objects retrieved is controlled by the optional ExplicitLoadingAttribute.Depth parameter. Its default value is 1.

Let us consider a simple example.

C#

class Book : XPObject {
    public string Name {
     get { return fName; }
     set { SetPropertyValue(nameof(Name), ref fName, value); }
 }
 string fName = "";

}
class Article : XPObject {
    [ExplicitLoading()]
    public Book theBook {
     get { return ftheBook; }
     set { SetPropertyValue(nameof(theBook), ref ftheBook, value); }
 }
 Book ftheBook;

}
class Topic : XPObject {
    [ExplicitLoading()]
    public Article theArticle {
     get { return ftheArticle; }
     set { SetPropertyValue(nameof(theArticle), ref ftheArticle, value); }
 }
 Article ftheArticle;

}
class Category : XPObject {
    public Topic theTopic {
     get { return ftheTopic; }
     set { SetPropertyValue(nameof(theTopic), ref ftheTopic, value); }
 }
 Topic ftheTopic;

}

VB.NET

Class Book
    Inherits XPObject
    Public Property Name() As String
        Get
            Return fName
        End Get
        Set(ByVal value as String)
            SetPropertyValue(NameOf(Name), fName, value)
        End Set
    End Property
    Private fName As String = ""

End Class

Class Article
    Inherits XPObject
    <ExplicitLoading()> _
    Public Property theBook() As Book
        Get
            Return ftheBook
        End Get
        Set(ByVal value as Book)
            SetPropertyValue(NameOf(theBook), ftheBook, value)
        End Set
    End Property
    Private ftheBook As Book

End Class

Class Topic
    Inherits XPObject
    <ExplicitLoading()> _
    Public Property theArticle() As Article
        Get
            Return ftheArticle
        End Get
        Set(ByVal value as Article)
            SetPropertyValue(NameOf(theArticle), ftheArticle, value)
        End Set
    End Property
    Private ftheArticle As Article

End Class

Class Category
    Inherits XPObject
    Public Property theTopic() As Topic
        Get
            Return ftheTopic
        End Get
        Set(ByVal value as Topic)
            SetPropertyValue(NameOf(theTopic), ftheTopic, value)
        End Set
    End Property
    Private ftheTopic As Topic

End Class

By marking theArticle and theBook properties with the ExplicitLoadingAttribute we have specified that the information about the Topic and Article classes’ properties will be retrieved in one query if the owning class is not deeper than 1 level from the root Category class. Since the Topic class has theArticle property of the Article type marked with the ExplicitLoadingAttribute and the Topic class is one level deep from the root Category class, the information to retrieve its property value will be included in the query. The Article class has theBook property of the Book type marked with the ExplicitLoadingAttribute. In this business model the Book class is two levels deeper than the root Category class, thus information for theBook property will not be included in the query, although this information will be used to generate a new query. If you specify ExplicitLoading(2) attribute for theBook property it will be enough to retrieve all the properties in the Category’s class.

Inheritance

Object

Attribute

ExplicitLoadingAttribute