在Entity Framework中保存实体的通用方法

Question

我正在尝试编写一个GenericEFRepository,它将被其他存储库使用.我有一个Save方法如下.

public virtual void Save(T entity) // where T : class, IEntity, new() And IEntity enforces long Id { get; set; }
{
    var entry = _dbContext.Entry(entity);

    if (entry.State != EntityState.Detached)
        return; // context already knows about entity, don't do anything

    if (entity.Id < 1)
    {
        _dbSet.Add(entity);
        return;
    }

    var attachedEntity = _dbSet.Local.SingleOrDefault(e => e.Id == entity.Id);
    if (attachedEntity != null)
        _dbContext.Entry(attachedEntity).State = EntityState.Detached;
    entry.State = EntityState.Modified;
}

您可以在以下代码的评论中找到问题

 using (var uow = ObjectFactory.GetInstance<IUnitOfWork>()) // uow is implemented like EFUnitOfWork which gives the DbContext instance to repositories in GetRepository
 {
    var userRepo = uow.GetRepository<IUserRepository>();

    var user = userRepo.Get(1);
    user.Name += " Updated";

    userRepo.Save(user);
    uow.Save(); // OK only the Name of User is Updated 
 }

 using (var uow = ObjectFactory.GetInstance<IUnitOfWork>())
 {
    var userRepo = uow.GetRepository<IUserRepository>();

    var user = new User 
    {
        Id = 1,
        Name = "Brand New Name"
    };

    userRepo.Save(user);
    uow.Save();

    // NOT OK
    // All fields (Name, Surname, BirthDate etc.) in User are updated
    // which causes unassigned fields to be cleared on db
 }

我能想到的唯一解决方案是通过存储库创建实体,userRepo.CreateEntity(id: 1)并且存储库将返回附加到DbContext的实体.但这似乎容易出错,仍然任何开发人员都可以使用new关键字创建实体.

您对此特定问题的解决方案建议是什么？

注意:我已经知道使用GenericRepository和IEntity接口的缺点和优点.因此,"不要使用GenericRepository,不要使用IEntity,不要在每个实体中放置长ID,不要做你想做的事情"评论也无济于事.

Answer 1

是的,它容易出错,但这只是EF和存储库的问题.您必须先创建实体并在设置要更新的任何数据之前附加它(Name在您的情况下),或者您必须为要保留的每个属性而不是整个实体设置修改状态(正如您可以想象的那样,开发人员可能会忘记做那).

第一个解决方案导致您的存储库执行以下特殊方法:

public T Create(long id) {
    T entity = _dbContext.Set<T>().Create();
    entity.Id = id;
    _dbContext.Set<T>().Attach(entity);
    return entity;
}

第二种解决方案需要像

public void Save(T entity, params Expression<Func<T, TProperty>>[] properties) {

    ...

    _dbContext.Set<T>().Attach(entity);
    if (properties.Length > 0) {
        foreach (var propertyAccessor in properties) {
            _dbContext.Entry(entity).Property(propertyAccessor).IsModified = true;
        }
    } else {
        _dbContext.Entry(entity).State = EntityState.Modified;
    }
}

你会称之为:

userRepository(user, u => u.Name);