实体框架添加实体也添加子实体

Question

我有一个表“Training”，它有一个“CreatedBy”列，它对“User”表有一个参照完整性。所以“CreatedBy”实际上是一个“用户”，代表插入培训记录的用户。

现在当我添加一个新的“Training”实体时，它的“CreatedBy”是一个旧的“User”。所以它也不应该尝试添加用户。但它确实失败了，因为它违反了唯一的键约束。

这是代码。我哪里错了？

    public int AddEntity(Training entity, bool isSaveInstantly)
    {
        this.trainersDeskDBModel.Trainings.AddObject(entity);

        if (isSaveInstantly)
        {
            this.trainersDeskDBModel.SaveChanges();
        }
        return entity.Id;
    }

    public int UpdateEntity(Training entity, bool isSaveInstantly)
    {
        this.trainersDeskDBModel.Trainings.ApplyCurrentValues(entity);
        if (isSaveInstantly)
        {
            this.trainersDeskDBModel.SaveChanges();
        }
        return entity.Id;
    }

    public int Save(Training entity, bool isSavedInstantly)
    {
        IEnumerable<Training> training = this.trainersDeskDBModel.Trainings.Where(x => x.Id == entity.Id);
        if (training != null && training.Count() > 0)
        {
            this.UpdateEntity(entity, isSavedInstantly);
        }
        else
        {
            this.AddEntity(entity, isSavedInstantly);
        }
        return entity.Id;
    }

Answer 1

如果你没有在添加新User的相同上下文中加载Training，那么EF必须通过附加它来告诉数据库中已存在User添加新Training之前的上下文：

public int AddEntity(Training entity, bool isSaveInstantly)
{
    this.trainersDeskDBModel.Users.Attach(entity.CreatedBy);
    this.trainersDeskDBModel.Trainings.AddObject(entity);

    if (isSaveInstantly)
    {
        this.trainersDeskDBModel.SaveChanges();
    }
    return entity.Id;
}