Ninject Conditional Self bind to change scope (For

Question

Within MVC Web Application DbContext binding work properly with InRequestScope()

 kernel.Bind<DbContext>().ToSelf().InRequestScope();
 kernel.Bind<IUnitOfWork<DbContext>>().To<UnitOfWork<DbContext>>();

But from a Task Scheduler call DbContext in InRequestScope() unable to update Db Table (without any error), until I change Binding to InSingletonScope() OR InThreadScope()

Question: So is their any way change scope to InSingletonScope() / InThreadScope() for a Task Scheduler Call. ?

// For Task Scheduler Call, I tried bellow bind, but not working properly

kernel.Bind<DbContext>().ToSelf()
.When(request => request.Target.Type.Namespace.StartsWith("NameSpace.ClassName"))
.InSingletonScope(); 

** And probably I miss some thing. Need help.

Code Snippet Updated

#region Commented Code

public EmailTask() : this
 ( DependencyResolver.Current.GetService<IMessageManager>(),
 , DependencyResolver.Current.GetService<IUnitOfWork<DbContext>>()) { }

#endregion



public EmailTask(IMessageManager messageManager, IUnitOfWork<DbContext> unitOfWork)
{
            this._messageManager = messageManager;
            this._unitOfWork = unitOfWork;
            ProcessEmail();

}

public class NonRequestScopedParameter : IParameter { ... }

public void ProcessEmail()
{
   var temp = SomeRepository.GetAll();

   SendEmail(temp);

   temp.Date = DateTime.Now;

   SomeRepository.Update(temp);

   unitOfWork.Commit();
}  

public class ExecuteEmailTask : ITask
{
  private readonly IResolutionRoot _resolutionRoot;
  private int _maxTries = 5;

  public ExecuteEmailTask(IResolutionRoot resolutionRoot)
  {
        _resolutionRoot = resolutionRoot;
  }

  public void Execute(XmlNode node)
        {
            XmlAttribute attribute1 = node.Attributes["maxTries"];
            if (attribute1 != null && !String.IsNullOrEmpty(attribute1.Value))
            {
                this._maxTries = int.Parse(attribute1.Value);
            }
            /// send email messages
            var task = _resolutionRoot.Get<EmailTask>(new NonRequestScopedParameter());
        }
}

In Web.Config

<ScheduleTasks>
     <Thread seconds="60">
        <task name="ExecuteEmailTask" type="namespace.ExecuteEmailTask, AssemblyName" enabled="true" stopOnError="false" maxTries="5"/>
      </Thread>      
    </ScheduleTasks>

In Global.asax

protected void Application_Start()
{
   /* intialize Task */
            TaskConfig.Init();

            TaskManager.Instance.Initialize(TaskConfig.ScheduleTasks);
            TaskManager.Instance.Start();
}

Ninject Bind Syntax

kernel.Bind<DbContext>().ToSelf().InRequestScope(); // Default bind

kernel.Bind<DbContext>().ToSelf()
                  .When(x => x.Parameters.OfType<NonRequestScopedParameter>().Any())
                  .InCallScope();  // For Scheduler

Note: EmailTask class also have SomeReposity as a Constructor Argument.

Queries:-

1. But what is the bind syntax to resolve TaskScheduler(IResolutionRoot resolutionRoot) ?
2. What is the configuration code to run TaskScheduler ?
3. As say to put IFakeDbContext directly into constructor, can this work with IUnitOfWork<FakeDbContext> ?

Problem

Task unable to call with Overloaded Constructor , it is only able to call TaskScheduler default Constructor.

Question 4: Can any way to invoke TaskScheduler(IResolutionRoot resolutionRoot) from TaskScheduler default constructor ?

Sample Code Snippet to create Task & run using System.Threading.Timer

private ITask createTask()
        {
            if (this.Enabled && (this._task == null))
            {
                if (this._taskType != null)
                {
                    this._task = Activator.CreateInstance(this._taskType) as ITask;
                }
                this._enabled = this._task != null;
            }
            return this._task;
        }

Question 5: Can I resolve TaskScheduler(IResolutionRoot resolutionRoot) here ?

Solved

public ExecuteEmailTask() : this(DependencyResolver.Current.GetService<IResolutionRoot>())

OR

 public ExecuteEmailTask() : this(new Bootstrapper().Kernel) { }

        public ExecuteEmailTask(IResolutionRoot resolutionRoot)
        {
            _resolutionRoot = resolutionRoot;
        }

Answer 1

First of, you should note that InSingletonScope() is usually a bad idea for DbContext's/Sessions. What happens if some other service changes data in the meantime? I would recommend investigating what effects this has.

---

For the scenario you first described, a correctly formulated .When(...) should work.

As an alternative to the .When(...) binding you could also use a .Named("FooBar") binding. The constructor of the scheduled task would then need to look like:

ctor(Named["FooBar"] DbContext dbContext);

However, note, that this only (easily) works in case you need to inject the DbContext into a single constructor. If the task features dependencies and these need the same DbContext instance, too, it gets a bit tricker.

Since you updated your answer and say that this is the case, i would recommend an entirely different approach: Using a request parameter as basis for the When(...) condition combined with InCallScope binding. See below for an example.

Brace yourself, this is ab it of code :) The implementation requires the ninject.extensions.NamedScope extension (nuget). I've also used xUnit and FluentAssertions nuget packages to execute the tests.

public class Test
{
    // the two implementations are just for demonstration and easy verification purposes. You will only use one DbContext type.
    public interface IFakeDbContext { }
    public class RequestScopeDbContext : IFakeDbContext { }
    public class CallScopeDbContext : IFakeDbContext { }

    public class SomeTask
    {
        public IFakeDbContext FakeDbContext { get; set; }
        public Dependency1 Dependency1 { get; set; }
        public Dependency2 Dependency2 { get; set; }

        public SomeTask(IFakeDbContext fakeDbContext, Dependency1 dependency1, Dependency2 dependency2)
        {
            FakeDbContext = fakeDbContext;
            Dependency1 = dependency1;
            Dependency2 = dependency2;
        }
    }

    public class Dependency1
    {
        public IFakeDbContext FakeDbContext { get; set; }

        public Dependency1(IFakeDbContext fakeDbContext)
        {
            FakeDbContext = fakeDbContext;
        }
    }

    public class Dependency2
    {
        public IFakeDbContext FakeDbContext { get; set; }

        public Dependency2(IFakeDbContext fakeDbContext)
        {
            FakeDbContext = fakeDbContext;
        }
    }

    public class TaskScheduler
    {
        private readonly IResolutionRoot _resolutionRoot;

        public TaskScheduler(IResolutionRoot resolutionRoot)
        {
            _resolutionRoot = resolutionRoot;
        }

        public SomeTask CreateScheduledTaskNow()
        {
            return _resolutionRoot.Get<SomeTask>(new NonRequestScopedParameter());
        }
    }

    public class NonRequestScopedParameter : Ninject.Parameters.IParameter
    {
        public bool Equals(IParameter other)
        {
            if (other == null)
            {
                return false;
            }

            return other is NonRequestScopedParameter;
        }

        public object GetValue(IContext context, ITarget target)
        {
            throw new NotSupportedException("this parameter does not provide a value");
        }

        public string Name
        {
            get { return typeof(NonRequestScopedParameter).Name; }
        }

        // this is very important
        public bool ShouldInherit
        {
            get { return true; }
        }
    }

    [Fact]
    public void FactMethodName()
    {
        var kernel = new StandardKernel();

        // this is the default binding
        kernel.Bind<IFakeDbContext>().To<RequestScopeDbContext>();

        // this binding is _only_ used when the request contains a NonRequestScopedParameter
        // in call scope means, that all objects built in the a single request get the same instance
        kernel.Bind<IFakeDbContext>().To<CallScopeDbContext>()
            .When(x => x.Parameters.OfType<NonRequestScopedParameter>().Any())
            .InCallScope();

        // let's try it out!
        var task = kernel.Get<SomeTask>(new NonRequestScopedParameter());

        // verify that the correct binding was used
        task.FakeDbContext.Should().BeOfType<CallScopeDbContext>();

        // verify that all children of the task get injected the same task instance
        task.FakeDbContext.Should()
            .Be(task.Dependency1.FakeDbContext)
            .And.Be(task.Dependency2.FakeDbContext);
    } 
}

Since, as you say, the task scheduler does not make use of the IoC to create the task, it only supports a parameterless constructor. In that case you can make use DependencyResolver.Current (however, note that i'm in no way an expert on asp.net /MVC so i'm not making any claims that this is thread safe or working 100% reliably):

public class TaskExecutor : ITask
{
    public TaskExecutor()
        : this(DependencyResolver.Current.GetService<IResolutionRoot>())
    {}

    internal TaskExecutor(IResolutionRoot resolutionRoot)
    {
        this.resolutionRoot = resolutionRoot;
    }

    public void Execute()
    {
        IFooTask actualTask = this.resolution.Get<IFooTask>(new NonRequestScopedParameter());
        actualTask.Execute();
    }
}