Load Objects

Sep 14, 2022
6 minutes to read

In your business logic you may need to fetch another object or a collection of objects to calculated values based on that object properties. You can implement the logic to obtain an existing object in a Controller or in a business class.

Load Objects in a Controller

Useful API

Object Space exposes the following methods to find an existing object.

IObjectSpace.FirstOrDefault<ObjectType>: Searches for the first object that matches the specified lambda expression. The generic parameter determines the object’s type.
IObjectSpace.FindObject: Searches for the first object that matches the specified criteria and is of the specified type.
IObjectSpace.FindObject<ObjectType>: Searches for the first object that matches the specified criteria. The object’s type is designated by the specified generic type parameter.
IObjectSpace.GetObject: Retrieves an object that corresponds to an IObjectRecord wrapper or object from another Object Space.
IObjectSpace.GetObjectByKey: Returns the persistent object that has the specified value for its key property.
IObjectSpace.GetObjectByKey<ObjectType>: Returns a persistent object of the type designated by the specified generic type parameter, with the specified value for its key property.
IObjectSpace.GetObjectByHandle: Returns the object with the specified handle.
IObjectSpace.IsObjectFitForCriteria: Specifies whether a particular object satisfies the specified criteria.

The following Object Space methods return a collection of objects.

IObjectSpace.GetObjects: Retrieves objects of the specified type from the current Object Space. Returns an IList collection.
IObjectSpace.GetObjects<T>: Retrieves objects of the specified type from the current Object Space. Returns an IList collection.
IObjectSpace.CreateCollection: Creates and initializes a collection of objects of the specified type, filtered according to the specified criteria and sorted according to the given sorting list.
IObjectSpace.GetObjectsQuery<T>: Gets a queryable data structure that provides functionality to evaluate queries against a specific business object type.

The following example uses a Parametrized Action to search for a Person by LastName, and then assigns all deferred tasks to that person.

C#
VB.NET

using System.Collections;
using DevExpress.Data.Filtering;
using DevExpress.ExpressApp;
using DevExpress.ExpressApp.Actions;
using DevExpress.Persistent.Base;
using DevExpress.Persistent.Base.General;
using DevExpress.Persistent.BaseImpl;
// ...
public class AssignTasksController : ObjectViewController<ListView, MainDemo.Module.BusinessObjects.DemoTask> {
    public AssignTasksController() {
        ParametrizedAction assignTasksAction = new ParametrizedAction(
            this, "AssignTasks", PredefinedCategory.Edit, typeof(string));
        assignTasksAction.Execute += AssignTasksAction_Execute;
    }
    private void AssignTasksAction_Execute(object sender, ParametrizedActionExecuteEventArgs e) {
        IObjectSpace objectSpace = View.ObjectSpace;
        string personParamValue = e.ParameterCurrentValue as string;
        CriteriaOperator personCriteria = CriteriaOperator.Parse("Contains([LastName], ?)", personParamValue);
        Person person = (Person)objectSpace.FindObject(typeof(Person), personCriteria);
        if(person != null) {
            CriteriaOperator taskCriteria = CriteriaOperator.Parse("[Status] = ?", TaskStatus.Deferred);
            IList tasks = objectSpace.GetObjects(
                typeof(MainDemo.Module.BusinessObjects.DemoTask), taskCriteria);
            foreach(MainDemo.Module.BusinessObjects.DemoTask task in tasks) {
                task.AssignedTo = person;
            }
        }
    }
}

Imports System.Collections
Imports DevExpress.Data.Filtering
Imports DevExpress.ExpressApp
Imports DevExpress.ExpressApp.Actions
Imports DevExpress.Persistent.Base
Imports DevExpress.Persistent.Base.General
Imports DevExpress.Persistent.BaseImpl
' ...
Public Class AssignTasksController
    Inherits ObjectViewController(Of ListView, MainDemo.Module.BusinessObjects.DemoTask)

    Public Sub New()
        Dim assignTasksAction As New ParametrizedAction(Me, "AssignTasks", PredefinedCategory.Edit, GetType(String))
        AddHandler assignTasksAction.Execute, AddressOf AssignTasksAction_Execute
    End Sub
    Private Sub AssignTasksAction_Execute(ByVal sender As Object, ByVal e As ParametrizedActionExecuteEventArgs)
        Dim objectSpace As IObjectSpace = View.ObjectSpace
        Dim personParamValue As String = TryCast(e.ParameterCurrentValue, String)
        Dim personCriteria As CriteriaOperator = CriteriaOperator.Parse("Contains([LastName], ?)", personParamValue)
        Dim person As Person = CType(objectSpace.FindObject(GetType(Person), personCriteria), Person)
        If person IsNot Nothing Then
            Dim taskCriteria As CriteriaOperator = CriteriaOperator.Parse("[Status] = ?", TaskStatus.Deferred)
            Dim tasks As IList = objectSpace.GetObjects( _
                GetType(MainDemo.Module.BusinessObjects.DemoTask), taskCriteria)
            For Each task As MainDemo.Module.BusinessObjects.DemoTask In tasks
                task.AssignedTo = person
            Next task
        End If
    End Sub
End Class

You can use the IObjectSpace.GetObjectsQuery<T> method to load objects. It allows you to use LINQ expressions to specify the required request.

C#
VB.NET

IQueryable<Product> query = this.ObjectSpace.GetObjectsQuery<Product>();

Dim query = Me.ObjectSpace.GetObjectsQuery(Of Product)()

Business logic can depend on a number of records in a database. In this scenario, use the IObjectSpace.GetObjectsCount method to get a number of records without fetching records.

In a Data Model (in an XPO Business Class)

An XPO Session available via the Session property in a business class implements methods to find and read an object from a database.

The following code snippet demonstrates how to initialize Employee‘s Address1 and Manager reference properties with new and existing objects:

File: MySolution.Module\BusinessObjects\Contact.cs(.vb)

C#
VB.NET

using DevExpress.Data.Filtering;
using DevExpress.Persistent.BaseImpl;
using DevExpress.Xpo;
// ...
public class Employee : Person {
    //...
    public override void AfterConstruction() {
        base.AfterConstruction();
        Address1 = new Address(Session);
        Address1.Country = Session.FindObject<Country>(CriteriaOperator.Parse("Name = 'USA'"));
        if(Address1.Country == null) {
            Address1.Country = new Country(Session);
            Address1.Country.Name = "USA";
        }
        Manager = Session.FindObject<Employee>(CriteriaOperator.Parse(
            "FirstName = 'John' && LastName = 'Doe'"));
    }
}

Imports DevExpress.Data.Filtering
Imports DevExpress.Persistent.BaseImpl
Imports DevExpress.Xpo
' ...
Public Class Employee
    Inherits Person
    '...
    Public Overrides Sub AfterConstruction()
        MyBase.AfterConstruction()
        Address1 = New Address(Session)
        Address1.Country = Session.FindObject(Of Country)(CriteriaOperator.Parse("Name = 'USA'"))
        If Address1.Country Is Nothing Then
            Address1.Country = New Country(Session)
            Address1.Country.Name = "USA"
            Address1.Country.Save()
        End If
        Manager = Session.FindObject(Of Employee)(CriteriaOperator.Parse( _
        "FirstName = 'John' && LastName = 'Doe'"))
    End Sub
End Class

To get a collection of objects in an XPO business class, instantiate a new XPCollection.

C#
VB.NET

using DevExpress.Persistent.BaseImpl;
using DevExpress.Xpo;
// ...
public class Order : BaseObject {    
    private XPCollection<Accessory> fAvailableAccessories;
    public XPCollection<Accessory> AvailableAccessories {
        get {
            if (fAvailableAccessories == null) {
                fAvailableAccessories = new XPCollection<Accessory>(Session);
            }
            return fAvailableAccessories;
        }
    }
}

public class Accessory : BaseObject { }

Imports DevExpress.Persistent.BaseImpl
Imports DevExpress.Xpo
' ...
Public Class Order
    Inherits BaseObject
    Private fAvailableAccessories As XPCollection(Of Accessory)
    Public ReadOnly Property AvailableAccessories() As XPCollection(Of Accessory)
        Get
            If fAvailableAccessories Is Nothing Then
                fAvailableAccessories = New XPCollection(Of Accessory)(Session)
            End If
            Return fAvailableAccessories
        End Get
    End Property
End Class

Public Class Accessory
    Inherits BaseObject
End Class

It’s possible to use the Session methods like GetObjects to fetch a collection of objects.

In an EF Core Business Class

Inside an EF Core business class, implement the IObjectSpaceLink interface in the class. XAF will automatically assign an Object Space instance to the IObjectSpaceLink.ObjectSpace property. Use the assigned Object Space APIs listed above to get an existing object.

The following code snippet demonstrates how to initialize the Address1 reference property with a new or existing object:

File: MySolution.Module\BusinessObjects\Employee.cs

using DevExpress.Data.Filtering;
using DevExpress.ExpressApp;
using DevExpress.Persistent.Base;
using DevExpress.Persistent.BaseImpl.EF;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace YourSolutionName.Module.BusinessObjects;
[DefaultClassOptions]
public class Employee : IXafEntityObject {
    [Key]
    public virtual Guid ID { get; set; }

    public virtual string Manager { get; set; }
    public void OnCreated() {
        // ...
        var address = ObjectSpace.FindObject<Address>(CriteriaOperator.FromLambda<Address>(a => a.Country == "USA"));
        if(address == null) {
            address = ObjectSpace.CreateObject<Address>();
            address.Country = "USA";
        }
        Address1 = address;
    }
    public virtual Address Address1 { get; set; }
    public void OnLoaded() { }
    public void OnSaving() { }
    public IObjectSpace ObjectSpace {
        get {
            return ((IObjectSpaceLink)this).ObjectSpace;
        }
    }
}
[DefaultClassOptions]
[DefaultProperty(nameof(Country))]
public class Address : BaseObject {
    public virtual string Country { get; set; }
    // ...
}
// Make sure that you use options.UseChangeTrackingProxies() in your DbContext settings.

Alternatively, you can inherit your class from the DevExpress.Persistent.BaseImpl.EF.BaseObject class as follows:

using DevExpress.Data.Filtering;
using DevExpress.ExpressApp;
using DevExpress.Persistent.Base;
using DevExpress.Persistent.BaseImpl.EF;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace YourSolutionName.Module.BusinessObjects;
[DefaultClassOptions]
public class Employee : BaseObject {
    public virtual string Manager { get; set; }
    public override void OnCreated() {
        // ...
        var address = ObjectSpace.FindObject<Address>(CriteriaOperator.FromLambda<Address>(a => a.Country == "USA"));
        if(address == null) {
            address = ObjectSpace.CreateObject<Address>();
            address.Country = "USA";
        }
        Address1 = address;
    }
    public virtual Address Address1 { get; set; }

}
[DefaultClassOptions]
[DefaultProperty(nameof(Country))]
public class Address : BaseObject {
    public virtual string Country { get; set; }
    // ...
}


// Make sure that you use options.UseChangeTrackingProxies() in your DbContext settings.

Controls

Tools

Controls and Extensions

Tools

Maintenance Mode

Controls

Tools

Controls and Extensions

Tools

Maintenance Mode

Load Objects in a Controller

In a Data Model (in an XPO Business Class)

In an EF Core Business Class