C# 如何通过实体键添加/删除与实体框架的多对多关系？

我试过：

using (Entities e = new Entities())
{
    EntityKey key = new EntityKey("Entities.Users", "UserId", 20);
    User user = new User { EntityKey = key};
    Role role = e.Roles.FirstOrDefault();
    //role.Users.Attach(user); //throws (when uncommented...) InvalidOperationException:
    //The object being attached to the source object is not attached to the same ObjectContext as the source object.
    role.Users.Add(user); //throws InvalidOperationException too:
    //The object cannot be added to the ObjectStateManager because it already has an EntityKey. Use ObjectContext.Attach to attach an object that has an existing key.
    e.SaveChanges();
}

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在未引发异常但未删除关系之前尝试使用Remove（）而不调用attach时。

请尝试以下操作：

User user = new User {UserId = 20};
e.AttachTo("Users", user);
Role role = e.Roles.FirstOrDefault();
role.Users.Add(user);
e.SaveChanges();

我发现使用存根实体（如上面的用户）比使用EntityKey容易得多

有关存根实体技术的更多信息，请参见本文

希望这有帮助

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Alex

在您的System.Data.Entity.DbContext类型示例中是“Entities”吗？后期研究：如果使用“AttachTo”，那么“Entities”必须是ObjectContext。LOL可能是一篇老文章。。。附加标签