Question

I’m new to LINQ so apologies if this is a simple answer. I’m trying to do a SQL join and have the following code based on examples I’ve seen on SO and elsewhere:

var query = from e in db.Events
    join ec in db.EventCategories on e.ID equals ec.EventID
    join c in db.Categories on ec.CategoryCode equals c.CategoryCode
    join ep in db.EventParticipants on e.ID equals ep.EventID
    join p in db.Participants on ep.ParticipantCode equals p.ParticipantCode
    select new { e, ec, c, ep, p };

This executes fine and when I run the debugger I can expand the Object and see that the query ran successfully. However, when I try to execute query.ToList() I can’t cast this into anything usable because it says that the list returned by query.ToList() is System.Collections.Generic.List.

Method #2:
Based on my own thoughts I tried creating the following struct:

public struct CalendarItem
    {
        public Event e;
        public EventCategory ec;
        public Category c;
        public EventParticipant ep;
        public Participant p;

        public CalendarItem(Event E, EventCategory EC, Category C, EventParticipant EP, Participant P)
        {
            e = E;
            ec = EC;
            c = C;
            ep = EP;
            p = P;
        }
    }

And then modifying the LINQ command to the following:

var query = from e in db.Events
    join ec in db.EventCategories on e.ID equals ec.EventID
    join c in db.Categories on ec.CategoryCode equals c.CategoryCode
    join ep in db.EventParticipants on e.ID equals ep.EventID
    join p in db.Participants on ep.ParticipantCode equals p.ParticipantCode
    select new CalendarItem(e, ec, c, ep, p);

In Visual Studio this checks out and it allows me to compile and everything looks great (i.e. I can loop over the list of CalendarItems), but I get a runtime error on query.ToList(): The member ‘e’ has no supported translation to SQL.

Answer 1

I’d make my CalandarItem a class with automatic properties:

public class CalendarItem
{
        public Event E{get;set;}
        public EventCategory EC{get;set;}
        public Category C{get;set;}
        public EventParticipant EP{get;set;}
        public Participant P{get;set;}
}

and use a object initializer on the select:

var query = from e in db.Events
    join ec in db.EventCategories on e.ID equals ec.EventID
    join c in db.Categories on ec.CategoryCode equals c.CategoryCode
    join ep in db.EventParticipants on e.ID equals ep.EventID
    join p in db.Participants on ep.ParticipantCode equals p.ParticipantCode
    select new CalendarItem{E=e, EC=ec, C=c, EP=ep, P=p};

I know this will work because I just happened to write a very similar bit of code about 2 minutes ago!