Write Business Object Code that Accesses Services (Use Session or IObjectSpace)

• Apr 29, 2024
• 3 minutes to read

You can obtain an IServiceProvider instance when you write Business Object code. This functionality is available in the following cases:

• XAF ASP.NET Core Blazor and Windows Forms applications that use XAF Application Builder.
• XAF Web API applications created by Solution Wizard.

XPO: Use Session.ServiceProvider

The Session class has constructors with the IServiceProvider parameter. XAF passes the IServiceProvider object when IObjectSpace creates a new instance of the Session object, if the IServiceProvider is available.

You can write code Business Object code that obtains any service. See the following example.

The code snippet below uses the IServiceProvider instance to obtain the ISecurityStrategyBase service. The service helps specify the CreatedBy property automatically when a new object is created. (Note: use this approach instead of the SecuritySystem static class. That class is outdated and cannot be used in XAF Web API applications.)

using DevExpress.ExpressApp.Security;
using DevExpress.Persistent.BaseImpl;
using DevExpress.Xpo;
using Microsoft.Extensions.DependencyInjection;

public class Task : BaseObject {
    ApplicationUser? createdBy;
    public Task(Session session) : base(session) { }

    ApplicationUser GetCurrentUser() { 
        return Session.GetObjectByKey<ApplicationUser>( 
            Session.ServiceProvider.GetRequiredService<ISecurityStrategyBase>().UserId);
    }

    protected override void OnSaving() {
        base.OnSaving();
        if (Session.IsNewObject(this)) {
            SetPropertyValueWithSecurityBypass(nameof(CreatedBy), GetCurrentUser());
        }
    }

    [ModelDefault(nameof(IModelCommonMemberViewItem.AllowEdit), "False")]
    public ApplicationUser? CreatedBy {
        get => createdBy;
        set => SetPropertyValue(nameof(CreatedBy), ref createdBy, value);
    }
} 

If you create a new instance of Session/UnitOfWork in your custom code, pass the IServiceProvider instance to the constructor as shown in following code sample:

using DevExpress.ExpressApp.Security;
using DevExpress.Persistent.BaseImpl;
using DevExpress.Xpo;
using Microsoft.Extensions.DependencyInjection;

public class Task : BaseObject {
    ApplicationUser? createdBy;
    public Task(Session session) : base(session) { }
     //...
    protected override void OnSaving() {
        base.OnSaving();
        using(var uow = new UnitOfWork(Session.ServiceProvider, Session.DataLayer)) {
            //...
            uow.CommitChanges();
        }
    }
}

EF Core: Use IObjectSpace.ServiceProvider

If you develop an XAF Entity Framework Core application and write Business Object code, use IObjectSpace.ServiceProvider to obtain the IServiceProvider object. You can obtain the IObjectSpace instance if the IObjectSpaceLink interface is implemented or if the Business Object class is a descendant of the BaseObject class that already implements the IObjectSpaceLink interface.

You can write code Business Object code that obtains any service. See the following example.

The code snippet below uses the IServiceProvider instance to obtain the ISecurityStrategyBase service. The service helps specify the CreatedBy property automatically when a new object is created. (Note: use this approach instead of the SecuritySystem static class. That class is outdated and cannot be used in XAF Web API applications.)

using DevExpress.ExpressApp.Security;
using DevExpress.Persistent.BaseImpl.EF;
using Microsoft.Extensions.DependencyInjection;
using WebApiEFAdditional.Module.BusinessObjects;

public class Task : BaseObject {
    [ModelDefault(nameof(IModelCommonMemberViewItem.AllowEdit), "False")]
    public virtual ApplicationUser? CreatedBy { get; set; }

    ApplicationUser GetCurrentUser() {
        return ObjectSpace.GetObjectByKey<ApplicationUser>(
            ObjectSpace.ServiceProvider.GetRequiredService<ISecurityStrategyBase>().UserId);
    }

    public override void OnSaving() {
        base.OnSaving();
        if (ObjectSpace.IsNewObject(this)) {
            SetPropertyValueWithSecurityBypass(nameof(CreatedBy), GetCurrentUser());
        }
    }
}

Note

You cannot use this technique in an Entity Framework Core Middle Tier Server application, since XAF does not use IObjectSpace for operations with Business Objects on the server side.

You can use the IObjectSpace.ServiceProvider property in any other part of an XAF application, but usually the XafApplication object is available, and you can use the XafApplication.ServiceProvider property instead.

Non-Persistent Objects

The NonPersistentObjectSpaceProvider class has constructors with the IServiceProvider parameter. You can obtain an IObjectSpace instance in a non-persistent Business Object class if it implements the IObjectSpaceLink interface. XAF passes the IServiceProvider to the new NonPersistentObjectSpaceProvider when it is created. If you create a new NonPersistentObjectSpaceProvider instance manually, you need to pass the IServiceProvider in its constructor to support dependency injection.