使用实体框架更新对象的所有字段

Question

I want to change all of an object properties using entity framwork.
after searching i got to have this:

Controller,action:

public ActionResult Test()
{
    var user = GetCurrentUser();
    user.FirstName = "BLAH BLAH";
    new UserRepository().UpdateUser(user);
    return RedirectToAction("Index");
}

and in my UserRepository:

public bool UpdateUser(ApplicationUser target)
{
     using (var db = new AppDatabase())
     {
        db.Entry(target).State = EntityState.Modified;
        db.SaveChanges();
        return true;
     }
}

but when i try execute i got this error

An entity object cannot be referenced by multiple instances of EntityChangeTracker.

so,any ways to fix or any better way?
using entity framework 6.0.0 and .net 4.5

public ApplicationUser GetCurrentUser()
{
   return UserManager.FindById(User.Identity.GetUserId());
}

Answer 1

Be sure that all objects came from the same context!

var userContextOne = new MyDbContext();
var user = userContextOne.Users.FirstOrDefault();

var AppDbContextTwo = new MyDbContext();

// Warning when you work with entity properties here! Be sure that all objects came from the same context!
db.Entry(target).State = EntityState.Modified;

AppDbContextTwo.SaveChanges();

The scond problem (not related to the exception!):

db.Entry(target).State = EntityState.Modified;

Why you are doing that?! You dont not have Detached Scenario? did you have disabled your Changetracker? anyway just execute DetectChanges and this method will find the changed data you do not have to do it by your self.

Answer 2

You should use same instance of db context for finding and updating, so you UserRepository can be:

 class UserRepository : IDisposable //using IDisposable to dispose db context
 {
      private AppDatabase _context;
      public UserRepository()
      {
           _context = new AppDatabase();
      }

      public ApplicationUser Find(string id)
      {
           return _context.Set<ApplicationUser>().Find(id);
      }

      public void Update(ApplicationUserentity entity)
      {
          _context.Entry(entity).State = EntityState.Modified;
          _context.SaveChanges();
      }

      public void Dispose()
      {
           _context.Dispose();
      }   
 }

You can use it in controller:

public ActionResult Test()
{
    using (var repository = new UserRepository())
    {
         var user = repository.Find(User.Identity.GetUserId());
         user.FirstName = "BLAH BLAH";
         repository.Update(user);
    }
    return RedirectToAction("Index");
}

I also think using some dependency injection framework would be beneficial for you. So go for it!!