In my MVC application, I have been using Repository pattern for DAL.

Now, when I do select one entity record and and update the entity field value and do Update operation then getting below error.

> 
> Attaching an entity of type 'DAL.User' 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."} System.Exception
> 
> 
> 

Below is repository stuff:

```
public void Update(TEntity entity)
{
    if (_context.Entry(entity).State != EntityState.Modified)
    {
         _dbSet.Attach(entity);
        _context.Entry(entity).State = EntityState.Modified;
    }
}

```

Calling as follow:
 In Bussines layer library:
 Manager class :

```
    private readonly IUnitOfWork _unitOfWork;
    private IRepository <User , int> UserRepository
    {
        get
        {
            return _unitOfWork.GetRepository<AccountUser, int>();
        }
    }
    public void UpdateUserEntity(UserDTO u)
    {
        try
        {

            User model = new User ();
            UserRepository.Update(Mapper.Map(u, model));
            _unitOfWork.SaveChanges();
        }
        catch (Exception ex)
        {
            throw;
        }
    }

```

Please guide me how I could resolve above error.