使用实体框架将现有实体添加到新创建的实体的集合中 [英] Using the entity framework to add existing entities to a collection on a newly created entity

问题描述

我正在使用实体框架创建新的订单。该订单包含一个联系人的集合，一对多关系。我想在订单创建时添加对现有联系人的引用。订单和联系实体对象。

I am using the Entity framework to create a new order. The order contains a collection of contacts, a many to many relationship. I want to add a reference to an existing contact on the order on creation of the order. Both Order and Contact a Entity Objects.

 Order order = new Order();

 //set details on order

 Contact contact = new Contact();

 EntityKey contactKey =
                    new EntityKey("OrderDetails.Contact",
                        "contact_id", contact.Key.Id);

 contact.EntityKey = contactKey;
 contact.contact_id = contact.Key.Id;

 order.Contact.Attach(contact);  // throws an exception!

 OrderDetails ordTable = new OrderDetails();
            ordTable.AddToOrder(order);
            int result = orgTable.SaveChanges();

当我去附加时，抛出这个异常：

When I go to attach, this exception is thrown:

当与此相关端相关联的源对象处于添加，删除或分离状态时，附加不是有效的操作。使用NoTracking合并选项加载的对象总是分离。

"Attach is not a valid operation when the source object associated with this related end is in an added, deleted, or detached state. Objects loaded using the NoTracking merge option are always detached."

我知道我可能错过了一个步骤，或者完全不了解实体框架如何处理多对多关系。

I know I'm probably missing a step or not fully understanding how the entity framework handles many-to-many relationships.

推荐答案

附件是不允许的，因为您尚未保存订单。调用添加告诉实体框架您要插入新的联系人。所以你只剩一个选项。您需要加载联系人。

"Attach" is not allowed because you haven't saved the order yet. Calling "Add" tells Entity Framework that you want to insert a new contact. So you are left with only one option. You need to load the contact.

这是最快的方法：

OrderDetails context = new OrderDetails();
Contact contact = context.GetObjectByKey(new EntityKey("OrderDetails.Contact", "contact_id", existingContactId));
order.Contact.Add(contact);

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