为什么实体框架在应该更新时插入？

Question

I use the following RIA Services call to register and return a Project entity.

// On Server; inside RIA Domain Service
[Invoke]
public Project CreateNewProject(String a_strKioskNumber)
{
  Decimal dProjectID = ObjectContext.RegisterProjectNumber(a_strKioskNumber)
                       .FirstOrDefault() ?? -1m;

  // Tried this but it returned zero (0)
  //int nChanged = ObjectContext.SaveChanges();

  var project = (from qProject in ObjectContext.Projects.Include("ProjectItems")
                 where qProject.ID == dProjectID
                 select qProject)
                 .FirstOrDefault();

  if (project == null)
    return null;

  return project;
}

As you can see, it calls a stored procedure that returns a project ID. It uses this ID to look up the Project entity itself and return it. When the Project entity is returned to the client it is detached. I attach it to the DomainContext and modify it.

// At Client
_activeProject = a_invokeOperation.Value; // <-- Detached
_context.Projects.Attach(_activeProject); // <-- Unmodified

if (_activeProject != null)
{
  _activeProject.AuthenticationType = "strong"; // <-- Modified
  _activeProject.OwnerID = customer.ID;
  _projectItems.Do(pi => _activeProject.ProjectItems.Add(pi));
  _activeProject.Status = "calculationrequired";
} 

At this point it has an entity state of Modified . When I submit changes it gives me an exception regarding a UNIQUE KEY violation as if it is trying to insert it rather than update it.

// At Client
_context.SubmitChanges(OnProjectSaved, a_callback);

I'm using the same DomainContext instance for all operations. Why should this not work?
What's going wrong? This is rather frustrating.

Edits:

I tried this (as suggested by Jeff):

[Invoke]
public void SaveProject(Project a_project)
{
  var project = (from qProject in ObjectContext.Projects
                 where qProject.ID == a_project.ID
                 select qProject)
                 .FirstOrDefault();

  project.SubmitDate = a_project.SubmitDate;
  project.PurchaseDate = a_project.PurchaseDate;
  project.MachineDate = a_project.MachineDate;
  project.Status = a_project.Status;
  project.AuthenticationType = a_project.AuthenticationType;
  project.OwnerID = a_project.OwnerID;
  project.ProjectName = a_project.ProjectName;
  project.OwnerEmail = a_project.OwnerEmail;
  project.PricePerPart = a_project.PricePerPart;
  project.SheetQuantity = a_project.SheetQuantity;
  project.EdgeLength = a_project.EdgeLength;
  project.Price = a_project.Price;
  project.ShipToStoreID = a_project.ShipToStoreID;
  project.MachiningTime = a_project.MachiningTime;

  int nChangedItems = ObjectContext.SaveChanges();
}

It did absolutely nothing. It didn't save the project.

Answer 1

What happens if you add a SaveProject method on the server side and send the object back to the server for saving?

I've not done EF with RIA Services, but I've always sent my objects back to the server for saving. I'm assuming that SubmitChanges call you are making wires up everything properly for you for sending it back to the server, but perhaps it is doing something wrong and handling it manually will fix it.

Answer 2

I dont have the source at the moment but I have seen it recommended that you use a new context for each operation in Silverlight. I ran into a similar problem today and it was because I was using a Service level context that was remembering previous values that I didnt want, I changed to creating a new context for each service call and the behavior became what I expected.

public void SaveResponses(ICollection<Responses> items, Action<SubmitOperation> callback)
        {
            try
            {
                SurveysDomainContext _context = new SurveysDomainContext();
                foreach (Responses item in items)
                {
                    _context.Responses.Add(item);
                }

                _context.SubmitChanges(callback, null);
            }
            catch (Exception)
            {

                throw;
            }

        }

Answer 3

As for the notion that one can't use a singleton global DomainContext, this is actually debatable. In my project I use a singleton DomainContext with no issues. In other projects, we have created a new DomainContext for different modules in the app where the entities are reused. There are definitely pros and cons. See: Strategies for Handling Your DomainContext (external blog)

Answer 4

It seems that the problem is that when you attach your project to the DomainContext it checks the _context.Projects entityset and isn't finding an entity with that primary key, and then assumes that the newly attached entity doesn't exist serverside yet and that submitting changes should insert it. A possible workaround might be to explicitly load the newly created Project into the DomainContext. It would ensure that it sets the correct state on the entity--that is, that the project already exists on the server and that that it's an update instance, rather than an insert instance.

So maybe something like:

//after your Project has already been created serverside with the invoke
_context.Load(_context.SomeQueryThatLoadsYourNewlyCreatedProject(), LoadBehavior.RefreshCurrent, (LoadOperation lo) => {
    Project project = lo.Entities.FirstOrDefault(); //is attached and has correct state
    if (project != null)
    {
        project.AuthenticationType = "strong";
        project.OwnerID = customer.ID;
        project.Do(pi => _activeProject.ProjectItems.Add(pi));
        project.Status = "calculationrequired";
        _context.SubmitChanges(); //hopefully will trigger an update, rather than an insert
    } 
});