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[ASP.net教程]分享关于Entity Framework 进行CRUD操作实验的结果


我们在使用Entity Framework框架进行CRUD时,经常会出现各种各样的错误,下面请看我的实验结果。

以下是只用一个上下文对象进行操作:

第一次:

      BlogDbContext blog = new BlogDbContext();      post = blog.Posts.Single(t => t.Id == 2);      post.AuthorId = 1;      blog.SaveChanges();

结果:成功

第二次:

      BlogDbContext blog = new BlogDbContext();      post = blog.Posts.Single(t => t.Id == 2);      post.Author = blog.Authors.Single(t => t.Id == 3);      blog.SaveChanges();

结果:成功

第三次:

      BlogDbContext blog = new BlogDbContext();      post = blog.Posts.Single(t => t.Id == 2);      post.AuthorId = 1;      post.Author = blog.Authors.Single(t => t.Id == 4);      blog.SaveChanges();

结果:失败,报错如下:

Conflicting changes to the role 'Post_Author_Target' of the relationship 'ConsoleApplication1.DDD.Infrastructure.Post_Author' have been detected.

第四次:

      BlogDbContext blog = new BlogDbContext();      post = blog.Posts.Single(t => t.Id == 2);      post.Author = new Author() { Id = 4 };      blog.Entry(post.Author).State = EntityState.Unchanged;      blog.SaveChanges();

结果:成功

第五次:

      BlogDbContext blog = new BlogDbContext();      post = blog.Posts.Single(t => t.Id == 2);      //author = new Author() { Id = 1, Name = "zwj" };//直接实例化或下面查询得出      author = blog.Authors.AsNoTracking().Single(t => t.Id == 3);      post.Author = author;      blog.SaveChanges();

结果:成功,但是Authors表中会新增一笔记录,并将新的ID赋值给Posts表;原因:Author与Post不在同一个上下文中,Post所在的上下文中追踪不到Author的信息,故当成新增。

以下是在两个不同的上下文中进行操作:

第六次:

      BlogDbContext blog = new BlogDbContext();      post = blog.Posts.AsNoTracking().Single(t => t.Id == 2);      //blog.Entry(post).State = EntityState.Detached;上面的AsNoTracking可以由这句实现      BlogDbContext blog2 = new BlogDbContext();      post.AuthorId = 5;      blog2.Entry(post).State = EntityState.Modified;      blog2.SaveChanges();

结果:成功

第七次:

      BlogDbContext blog = new BlogDbContext();      post = blog.Posts.AsNoTracking().Single(t => t.Id == 2);      BlogDbContext blog2 = new BlogDbContext();      post.Author = blog2.Authors.Single(t => t.Id == 5);      blog2.Entry(post).State = EntityState.Modified;      blog2.SaveChanges();

结果:失败,报错如下:

A referential integrity constraint violation occurred: The property value(s) of 'Author.Id' on one end of a relationship do not match the property value(s) of 'Post.AuthorId' on the other end.

第八次:

      BlogDbContext blog = new BlogDbContext();      post = blog.Posts.AsNoTracking().Single(t => t.Id == 2);      BlogDbContext blog2 = new BlogDbContext();      author = blog2.Authors.AsNoTracking().Single(t => t.Id == 1);      post.Author = author;      blog2.Entry(post).State = EntityState.Modified;      blog2.SaveChanges();

结果:失败,报错同第七次

第九次:

      BlogDbContext blog = new BlogDbContext();      post = blog.Posts.AsNoTracking().Single(t => t.Id == 2);      author = blog.Authors.AsNoTracking().Single(t => t.Id == 3);      BlogDbContext blog2 = new BlogDbContext();      post.Author = author;      blog2.Entry(post).State = EntityState.Modified;      blog2.SaveChanges();

结果:失败,报错同第七次

第十次:

      BlogDbContext blog = new BlogDbContext();      post = blog.Posts.AsNoTracking().Single(t => t.Id == 2);      BlogDbContext blog2 = new BlogDbContext();      author = new Author() { Id = 1, Name = "zwj" };      post.Author = author;      blog2.Entry(post).State = EntityState.Modified;      blog2.SaveChanges();

结果:失败,报错同第七次

第十一次:

      BlogDbContext blog = new BlogDbContext();      post = blog.Posts.AsNoTracking().Single(t => t.Id == 2);      BlogDbContext blog2 = new BlogDbContext();      author = blog2.Authors.Single(t => t.Id == 1);      post.Author = author;      post.AuthorId = author.Id;      blog2.Entry(post).State = EntityState.Modified;      blog2.SaveChanges();

结果:成功,但我认为主要是通过赋值AuthorId来完成的,与第六次相同,去掉赋值AuthorId,则与第七次相同的报错

第十二次:

      BlogDbContext blog = new BlogDbContext();      post = blog.Posts.AsNoTracking().Single(t => t.Id == 2);      BlogDbContext blog2 = new BlogDbContext();      author = blog2.Authors.Single(t => t.Id == 3);      blog2.Entry(post).Reference(t => t.Author).CurrentValue = author;      blog2.Entry(post).State = EntityState.Modified;      blog2.SaveChanges();

结果:失败,报错同第七次

第十三次:

      BlogDbContext blog = new BlogDbContext();      post = blog.Posts.AsNoTracking().Single(t => t.Id == 2);      BlogDbContext blog2 = new BlogDbContext();      blog2.Posts.Attach(post);      post.Author = blog2.Authors.Single(t => t.Id == 1);      blog2.SaveChanges();

结果:成功

 

最后得出结论:

1.在同一个上下文中,不论是采用直接赋值导航属性或是直接赋值外键属性,除不能同时对导航属性及外键属性赋不相关联的值外,都可以成功;

2.不在同一个上下文中,若想在完成CUD时,则必需先确保要进行操作的实体处于Detached状态,然后再进行相应的更新,涉及导航属性时,只能采用赋值外键属性,不能通过导航属性直接赋值,否则会报错(这个我觉得是个BUG,不知大家有什么好的解决办法没有),若采用先在新的上下文中Attached,再进行更新操作则与第1条结论相同。