How to use a lookup table in entity?

Question

I have imported my database into entity. All is well except my lookup tables aren't easily accessible anymore.

Example I have a Users table and a Friends table. Many unique users can have the same friends. To handle this I have a Users_Friends table consisting of 2 columns (UserID and FriendID).

I want to be able to query this table against a unique userID to pull all the FriendIDs associated with that particular user. But when I try and do

using (var db = new GameAlertDBEntities())
{
    var friendIDs = db.Users_Friends.
}

I immediately get told cannot resolve symbol Users_Friends. Which I stop there trying to figure out how to resolve the symbol before moving forward. Oddly enough entity finds all my other tables just none of my look up tables.

Answer 1

Many-to-many relationships aux tables are not abstracted into EF tables. Instead you can directly acceess list of related entities like this:

using (var db = new GameAlertDBEntities())
{
    var user = db.Users.First(); // or any other query for user
    var friends = user.Friends;
}

How does this happen? Entity framework recognizes such relationships during import and does all the work behind the scenes.

Answer 2

如果UserId和FriendId未标记为外键，则必须通过简单查询来查找朋友

var userFriends = db.Users.Friends.ToList();