如何在使用依赖注入和工作单元时获取生成的项目 ID？

Question

I am using ASP.NET MVC5, Entity Framework 6, Dependency Injection and Unit Of Work.

I am facing issue while saving a new item in the database. I am not able to get the newly generated ID of the just inserted item.

Below is a sample of my code, just to know more about my issue:

Here's my service

public class UserService : IUserService
{
    IUnitOfWork _unitOfWork;
    IUserRepository _userRepository;

    public UserService(IUnitOfWork unitOfWork, IUserRepository UserRepository)
    {
        _unitOfWork = unitOfWork;
        _userRepository = UserRepository;
    }
    public int Create(UserDTO entity)
    {
        if(entity == null)
        {
            throw new ArgumentNullException("entity");
        }

        entity = _userRepository.Add(entity);
        _unitOfWork.Commit();

        return entity.UserID;
    }
}

Here's my repository

public virtual TEntityDTO Add(TEntityDTO entity)
{
    var item = Mapper.Map<TEntityDTO, TEntity>(entity);
    var createItem = Mapper.Map<TEntity, TEntityDTO>(context.Set<TEntity>().Add(item));
    return createItem;
}

Here's my unit of work

public int Commit()
{
    // Save changes with the default options
    return _dbContext.SaveChanges();
}

Answer 1

I do not know Entity Framework but the problem looks obvious to me.

The line entity=_userRepository.Add(entity); calls Add method of Repository. In your Add method in Repository, you are adding an entity and then mapping it back to DTO. You are then returning mapped DTO. Note that DTO is detached here from your entity. It cannot anymore reflect the changes in Entity.

Then in your service, you call _unitOfWork.Commit(); . This flushes the changes to database and here actually the new ID is generated. This new ID is reflected in your entity. But as you are dealing with DTO which is no more connected to Entity, you cannot see that newly generated ID.

What is the solution then? I do not know, this depends on your overall architecture.

1. Return the entity without mapping it with DTO.
2. Commit inside repository instead of Service.