Create a left join using Microsoft Entity Framework (EF). The query below is used to return a list of users without friends.
var query = from users in myDbContext.Users
join userFriends in myDbContext.UserFriends on users.Id equals userFriends.UserId into myJoinedTable
from leftJoin in myJoinedTable.DefaultIfEmpty()
where leftJoin.Id == null
select users;
allUsers = query.ToList();