分享關於Entity Framework 進行CRUD操作實驗的結果

標籤：

我們在使用Entity Framework架構進行CRUD時，經常會出現各種各樣的錯誤，下面請看我的實驗結果。

以下是只用一個內容物件進行操作：

第一次：

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

結果：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();

結果：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();

結果：失敗，報錯如下：

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();

結果：成功

第五次：

            BlogDbContext blog = new BlogDbContext();            post = blog.Posts.Single(t => t.Id == 2);            //author = new Author() { Id = 1, Name = "zwj" };//直接執行個體化或下面查詢得出            author = blog.Authors.AsNoTracking().Single(t => t.Id == 3);            post.Author = author;            blog.SaveChanges();

結果：成功，但是Authors表中會新增一筆記錄，並將新的ID賦值給Posts表；原因：Author與Post不在同一個上下文中，Post所在的上下文中追蹤不到Author的資訊，故當成新增。

以下是在兩個不同的上下文中進行操作：

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可以由這句實現            BlogDbContext blog2 = new BlogDbContext();            post.AuthorId = 5;            blog2.Entry(post).State = EntityState.Modified;            blog2.SaveChanges();

結果：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();

結果：失敗，報錯如下：

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();

結果：失敗，報錯同第七次

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();

結果：失敗，報錯同第七次

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();

結果：失敗，報錯同第七次

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();

結果：成功，但我認為主要是通過賦值AuthorId來完成的，與第六次相同，去掉賦值AuthorId，則與第七次相同的報錯

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();

結果：失敗，報錯同第七次

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();

結果：成功

 

最後得出結論：

1.在同一個上下文中，不論是採用直接賦值導覽屬性或是直接賦值外鍵屬性，除不能同時對導覽屬性及外鍵屬性賦不相關聯的值外，都可以成功；

2.不在同一個上下文中，若想在完成CUD時，則必需先確保要進行操作的實體處於Detached狀態，然後再進行相應的更新，涉及導覽屬性時，只能採用賦值外鍵屬性，不能通過導覽屬性直接賦值，否則會報錯（這個我覺得是個BUG，不知大家有什麼好的解決辦法沒有），若採用先在新的上下文中Attached，再進行更新操作則與第1條結論相同。

分享關於Entity Framework 進行CRUD操作實驗的結果