Updating existing data in EF 6 throws exception -

问题:

I am trying to update a record using Entity Framework 6, code-first, no fluent mapping or a tool like Automapper.

The entity(Employee) has other composite properties associated with it like Addreess(collection), Department

It is also inherited from a base called User

The save method is as follows, with _dbContext being the DbConext implementation

        public bool UpdateEmployee(Employee employee)
        {
            var entity = _dbContext.Employees.Where(c => c.Id == employee.Id).AsQueryable().FirstOrDefault();
            if (entity == null)
            {
                _dbContext.Employees.Add(employee);
            }
            else
            {
                _dbContext.Entry(employee).State = EntityState.Modified; // <- Exception raised here
                _dbContext.Employees.Attach(employee);

            }

            return _dbContext.SaveChanges() > 0;

        }

I keep getting the error:

Attaching an entity of type 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.

I have tried the following:

1. Attaching before setting to EntityState.Modified
2. Adding AsNoTracking() on querying if the object exists(No exception but DB is not updated) - https://stackoverflow.com/a/23228001/919426
3. Saving using the base entity _dbContext.Users instead of the Employee entity - https://stackoverflow.com/a/25575634/919426

None of which is working for me now.

What could I have gotten wrong for some of those solutions not to work in my situation?

回答1:

EF already includes a way to map properties without resorting to Automapper, assuming you do not have navigation properties to update:

public bool UpdateEmployee(Employee employee)
    {
        var entity = _dbContext.Employees.Where(c => c.Id == employee.Id).AsQueryable().FirstOrDefault();
        if (entity == null)
        {
            _dbContext.Employees.Add(employee);
        }
        else
        {
            _dbContext.Entry(entity).CurrentValues.SetValues(employee);              
        }

        return _dbContext.SaveChanges() > 0;

    }

This usually generates a better SQL statement since it will only update the properties that have changed.

If you still want to use the original method, you'll get rid of entity from the context, either using AsNoTracking (not sure why it didn't update in your case, it should have no effect, so the problem might be something else) or as modifying your query to prevent it from materializing the entity in the first place, using something like bool exists = dbContext.Employees.Any(c => c.Id == employee.Id) for example.

回答2:

This worked for myself

var aExists = _db.Model.Find(newOrOldOne.id);
if(aExists==null)
{
    _db.Model.Add(newOrOldOne);
}
else
{
    _db.Entry(aExists).State = EntityState.Detached;
    _db.Entry(newOrOldOne).State = EntityState.Modified;
}

回答3:

I've encountered the same thing when using a repository and unit of work pattern (as documented in the mvc4 with ef5 tutorial).

The GenericRepository contains an Update(TEntity) method that attempts to Attach then set the Entry.State = Modified. The up-voted 'answer' above doesn't resolve this if you are going to stick to the uow / repo pattern.

I did attempt to use the detach process prior to the attach, but it still failed for the same reason as indicated in the initial question.

The reason for this, it turns out, is that I was checking to see if a record existed, then using automapper to generate an entity object from my dto prior to calling update().

By checking for the existance of that record, i put the entity object in scope, and wasn't able to detach it (which is also the reason the initial questioner wasn't able to detach)... Tt tracked the record and didn't allow any changes after I automapper'ed the dto into an entity and then attempted to update.

Here's the generic repo's implementation of update:

public virtual void Update(TEntity entityToUpdate)
{
    dbSet.Attach(entityToUpdate);
    context.Entry(entityToUpdate).State = EntityState.Modified;
}

This is my PUT method (i'm using WebApi with Angular)

[HttpPut]
public IHttpActionResult Put(int id, Product product)
{
    IHttpActionResult ret;
    try
    {
        // remove pre-check because it locks the record
        // var e = unitOfWork.ProductRepository.GetByID(id);
        //  if (e != null) {
        var toSave = _mapper.Map<ProductEntity>(product);
        unitOfWork.ProductRepository.Update(toSave);
        unitOfWork.Save();
        var p = _mapper.Map<Product>(toSave);
        ret = Ok(p);
        // }
        // else
        //    ret = NotFound();
    }
    catch (DbEntityValidationException ex)
    {
        ret = BadRequest(ValidationErrorsToMessages(ex));
    }
    catch (Exception ex)
    {
        ret = InternalServerError(ex);
    }
    return ret;
}

As you can see, i've commented out my check to see if the record exists. I guess i'll see how it works if I attempt to update a record that no longer exists, as i no longer have a NotFound() return opportunity.

So to answer the initial question, i'd say don't look for entity==null before making the attempt, or come up with another methodology. maybe in my case, i could dispose of my UnitOfWork after discovery of the object and then do my update.

回答4:

You need to detach to avoid duplicate primary key exception whist invoking SaveChanges

db.Entry(entity).State = EntityState.Detached;