属性“Id”是对象的关键信息的一部分，不能修改 [英] The property 'Id' is part of the object's key information and cannot be modified
问题描述
我使用的是Entity Framework 4.0，有一个愚蠢的问题，我无法确定。
i'm using Entity Framework 4.0 and having a silly problem that i can't figure out.
我有两个表：
- 联系人：Id（主键），值，ContactTypeId（ContactType的外键）
- ContactType：Id（主键） ，类型（家庭，单元格，工作等）
实体框架创建了以下两个实体：
Entity Framework created the following two entities:
- 联系人：Id，Value，ContactType（导航属性）
- ContactType：Id，Type，Contact（Navigation Property） li>
- Contact: Id, Value, ContactType (Navigation Property)
- ContactType: Id, Type, Contact (Navigation Property)
我正在使用以下代码获取联系人并更新该特定联系人的联系人类型：
I'm using the following code to get the contact and update the contact type for that particular contact:
Contact contact = dbContext.Contacts.Single(c => c.Id == 12345);
contact.ContactType.Id = 3;
抛出以下异常：
The property 'Id' is part of the object's key information and cannot be modified.
看起来很简单！我没有得到它
It looks so simple! I don't get it!
推荐答案
框架创建的实体没有contact.ContactTypeId属性。它会自动删除它，并在联系人实体内创建了ContactType关联。
The entity that was created by the framework doesn't have a contact.ContactTypeId property. It automatically removed it and created the ContactType association inside the Contact entity.
正如你所建议的那样，让它工作的方式是通过查询数据库并将其分配给contact.ContactType。例如：
The way to get it to work, as you suggested, is to create a ContactType object by querying the database and assigning it to contact.ContactType. For example:
Contact contact = dbContext.Contacts.Single(c => c.Id == 12345);
ContactType contactType = dbContext.ContactType.Single(c => c.Id == 3);
contact.ContactType = contactType;
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