工作单元/存储库模式以及使用EF更新实体

Question

I'm trying to get to know UoW pattern a bit better as I like its concept, but currently I'm having a hard times saving entities.

The problem is that when my Edit (POST) action in my controller fires only parent entity gets saved and the child entities are intact ie I get the following error:

Attaching an entity of type 'Access.Models.ApplicationParameter' failed because another entity of the same type already has the same primary key value. This can happen when using the 'Attach' method or setting the state of an entity to 'Unchanged' or 'Modified' if any entities in the graph have conflicting key values. This may be because some entities are new and have not yet received database-generated key values. In this case use the 'Add' method or the 'Added' entity state to track the graph and then set the state of non-new entities to 'Unchanged' or 'Modified' as appropriate.

Note: Parent entity Application can have multiple child ApplicationParameter entities.

Controller

    [HttpPost]
    public ActionResult Edit(ApplicationVM applicationVM)
    {
        Application application = ViewModelToModel(applicationVM);
        uow.ApplicationRepository.Update(application);

        foreach (var applicationParameterVM in applicationVM.ApplicationParameters)
        {
            ApplicationParameter applicationParameter = ViewModelToModel(applicationParameterVM);

            bool exists = uow.ApplicationParameterRepository.Exists(applicationParameter.idApplicationParameter);

            if (exists)
            {
                uow.ApplicationParameterRepository.Update(applicationParameter);
            }
            else
            {
                uow.ApplicationParameterRepository.Insert(applicationParameter);
            }
        }

        uow.Save();
        return View(applicationVM);
    }

ApplicationParameterRepository.cs (just Update snippet)

    public void Update(ApplicationParameter entity)
    {
        db.Entry(entity).State = EntityState.Modified;
    }

UOW.cs

public class UnitOfWork : IDisposable
{
    private AMEntities db = null;

    public UnitOfWork()
    {
        db = new AMEntities();
    }

    //Add all the repository handles here
    IApplicationRepository applicationRepository = null;
    IApplicationParameterRepository applicationParameterRepository = null;
    IApplicationUserRepository applicationUserRepository = null;

    //Add all the repository getters here
    public IApplicationRepository ApplicationRepository
    {
        get
        {
            if (applicationRepository == null)
            {
                applicationRepository = new ApplicationRepository(db);
            }
            return applicationRepository;
        }
    }
    public IApplicationParameterRepository ApplicationParameterRepository
    {
        get
        {
            if (applicationParameterRepository == null)
            {
                applicationParameterRepository = new ApplicationParameterRepository(db);
            }
            return applicationParameterRepository;
        }
    }
    public IApplicationUserRepository ApplicationUserRepository
    {
        get
        {
            if (applicationUserRepository == null)
            {
                applicationUserRepository = new ApplicationUserRepository(db);
            }
            return applicationUserRepository;
        }
    }

    public void Save()
    {
        db.SaveChanges();
    }

    private bool disposed = false;

    protected virtual void Dispose(bool disposing)
    {
        if (!this.disposed)
        {
            if (disposing)
            {
                db.Dispose();
            }
        }
        this.disposed = true;
    }

    public void Dispose()
    {
        Dispose(true);
        GC.SuppressFinalize(this);
    }
}

Question: What should I do to have those child entities saved?

Answer 1

Ensure you establish the relationship between applicationParameter and application . There are at least three ways to do that using navigation properties or Ids, and I don't see in your code a line like this:

1.

// if application have unique Id, for example it already has been saved in db
applicationParameter.ApplicationId = application.Id; 

2.

applicationParameter.Application = application;

3.

//if application is a EF-generated proxy 
application.ApplicationParameters.Add(applicationParameter); 

Also, in simple cases you don't need to set EntityState if entity has been added to context properly.

Answer 2

You have 2 options as far as I see it.

1. The easiest thing to do would be to get the entity at the start of your Edit action. If the result is null, then add a new one otherwise update the entity with the new values and save. This will ensure the parent entity and all children are in the same context.

2. The other way is to use self tracking entities. Take a look at Self Tracking Entities . This way you handle the state of your entities and not EF.

The issue is you have only set the state of the parent to updated, each childs state is still added, so its trying to add the child entities instead of update them.