How to perform a left outer join using Entity Framework using navigation properties - entity-framework

Question

I'm trying to find out how I would define the code first navigation properties on these two classes to perform something similiar to this query:
SELECT USERID, FIRSTNAME, LASTNAME, COURSEID, NAME
FROM User
LEFT OUTER JOIN Course ON User.USERID = Course.USERID
WHERE COURSEID = 1
So I'm trying to find a list of users together with if they have attended a certain course.
public class User
{
public int UserId {get;set; }
public string FirstName {get;set;}
public string LastName {get;set;}
public virtual ICollection<Course> Courses { get; set; }
}
public class Course
{
public int CourseId { get;set; }
public int UserId { get;set; }
public string Name { get;set; }
public virtual User User {get;set;}
}
If I was to write a query to achieve this
var u = Users.Where(x => x.Courses.Any(x => x.CourseId = 1));
This does a subquery, which is not what I wanted (as people who didnt attend the course would not show).
How would the navigation property be defined?
HasMany(t => t.Courses).WithOptional(t => t.User).HasForeignKey(t => t.UserId);

Answer 1

Check this link:
http://msdn.microsoft.com/en-us/library/vstudio/bb397895.aspx
Left outer joins in LINQ are done via DefaultIfEmpty method.

Answer 2

var u = Users.Select ( x => new {
User = x,
AttendedCourse = x.Courses.Any()
} );
For specific course id,
var u = Users.Select ( x => new {
User = x,
AttendedCourse = x.Courses.Any( c => c.CourseID == 1 )
} );
Sub query is the only way to write related queries, However, EF will choose the best suitable join type and will give you correct results. And EF can manage mostly all kinds of queries without doing joins.