实体框架 4.1 修改对象和子集合

发布于 2024-11-03 14:44:51 字数 365 浏览 0 评论 0原文

如果我有 Book 对象，其中包含 Comments 子集合，我可以与实体框架一起更新 Book 和 Comments 列表吗？

我尝试过：

_context.Books.Attach(book);
_context.ObjectStateManager.ChangeObjectState(book, EntityState.Modified);
_context.SaveChanges();

但没有运气...

在第一行出现以下错误：

ObjectStateManager 中已存在具有相同键的对象。 ObjectStateManager 无法跟踪具有相同键的多个对象

原文

If I have Book object which has a child collection of Comments, Can I update the Book and list of Comments together with entity framework?

I have tried :

_context.Books.Attach(book);
_context.ObjectStateManager.ChangeObjectState(book, EntityState.Modified);
_context.SaveChanges();

with no luck...

getting the following error on the first line:

An object with the same key already exists in the ObjectStateManager. The ObjectStateManager cannot track multiple objects with the same key

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疯了 2024-11-10 14:44:51

您很可能存在循环依赖（书籍有对评论的外键引用，评论又回到书籍）。在这种情况下，EF 内的 UpdateTranslator 无法确定依赖顺序。据我所知，在这种开发模型中，没有办法向 EF 传递提示来指示顺序是什么。

解决这个问题的最常见方法（我见过）是进行两阶段提交。对书籍进行更改并保存，然后对评论进行更改并保存。我发现使用代码优先方法允许您更具体地了解关系，从而解决我遇到的许多问题。

编辑：
下面是一个示例：

using (var context = new BookContext())
{
    book.Title = "This is the new title";
    context.SaveChanges();

    book.Comments.Add(new Comment("This is a comment"));
    context.SaveChanges();
}

如果存在循环依赖项，则无法通过单次调用 SaveChanges 来完成上述操作。

More than likely you have a circular dependency (Books has a foreign key reference to Comments, and Comments back to Books). In this case, the UpdateTranslator within EF is unable to determine the dependency order. As far as I can tell, in this model of development, there is no way to pass a hint to EF to indicate what the order is.

The most common way to solve this (that I have seen) is to do a two-phase commit. Make a change to the Book, save it, then make a change to Comments, and save that. I have found that using the Code First approach allows you to be more specific about the relationships and thereby fix many of the problems that I've had.

Edit:
Here's an example:

using (var context = new BookContext())
{
    book.Title = "This is the new title";
    context.SaveChanges();

    book.Comments.Add(new Comment("This is a comment"));
    context.SaveChanges();
}

If there is a circular dependency, you could not do the above with a single call to SaveChanges.

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