.net Entity Framework 中的导航属性有什么用？
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What are Navigation Properties in Entity Framework for?
提问by chobo2
I see in my EF diagram alot of these navigation properties but not sure what they are really for. Like I see in lots of my tables I have aspnet_Users properties.
我在我的 EF 图中看到了很多这些导航属性，但不确定它们的真正用途。就像我在很多表中看到的那样，我有 aspnet_Users 属性。
What are these for? Do they help for joins? or what?
这些是干什么用的？他们对加入有帮助吗？或者是什么？
Error 2
Error 3007: Problem in Mapping Fragments starting at lines 1201, 1423:
Non-Primary-Key column(s) [Field2] are being mapped in both fragments
to different conceptual side properties - data inconsistency is possible
because the corresponding conceptual side properties can be independently
modified.
回答by marc_s
A navigation property allows you to navigate from one entity to a "connected" entity.
导航属性允许您从一个实体导航到“连接”实体。
E.g. if your user is connected to a role, you can use the "Role" navigation to read and inspect the role associated with the user.
例如，如果您的用户连接到某个角色，您可以使用“角色”导航来读取和检查与用户关联的角色。
EDIT:
编辑：
If you want to load the user with LINQ-to-Entities, and also look at its "Role" navigation property, you have to explicitly include the "Role" entity in your LINQ query - EF does NOTload those navigation properties automatically for you.
如果要加载使用LINQ到实体的用户，同时也看看它的“角色”导航属性，你必须明确地包含了“角色”的实体在你的LINQ查询- EF确实不为你自动加载的导航性能.
// load user no. 4 from database
User myUser = from u in Users.Include("Role")
where u.ID = 4
select u;
// look at the role the user has
string roleName = myUser.Role.Name;
OR:
或者：
// load user no. 4 from database
User myUser = from u in Users
where u.ID = 4
select u;
// check to see if RoleReference is loaded, and if not, load it
if(!myUser.RoleReference.IsLoaded)
{
myUser.RoleReference.Load();
// now, the myUser.Role navigation property should be loaded and available
}
// look at the role the user has
string roleName = myUser.Role.Name;
It's basically a programmatic equivalent to a foreign key relationship in a database - a connection between two objects. It basically "hides" or resolves a join between two tables (or two entities, in EF speak).
它基本上是一个编程等价于数据库中的外键关系 - 两个对象之间的连接。它基本上“隐藏”或解析两个表（或两个实体，在 EF 中）之间的连接。
Marc
马克
