Linq To Sql return from function as IQueryable

Question

Ok, I have managed to get the following working

public IQueryable getTicketInformation(int ticketID)
{
    var ticketDetails = from tickets in _context.ticke         


        

Answer 1

You mean:

select new MyObject { TicketId = tickets.ticket_id,
     Title = tickets.title, ...};

(note I tweaked the names slightly to be more C#-idiomatic)

This is an "object initializer" that creates a new MyObject (per record) and assigns the properties from the source data. What you had was an "anonymous type" initializer, which isn't the same. Note that if you have a non-default constructor, you could also use something like:

select new MyObject(tickets.ticket_id, tickets.title);

which uses the specified constructor, passing in the supplied values from the source data.

This will then be IQueryable<MyObject>; you don't need to call .AsQueryable(). Note it would be better for your function to return the typed form (IQueryable<MyObject>) than the untyped IQueryable.

Answer 2

Gents, It all makes sense as long as you're only returning single table, but what if there's two or more to be returned???

RPDTDataContext smdt = new RPDTDataContext();
var projectedUsers = smdt.SM_Users.Join(
        smdt.SM_CTSGroups, u => u.CtsGroupID, c => c.id, 
        (u, c) => new { CTSGroup = c.Name, UserName = u.Name, u.EmpID, u.Email });
return projectedUsers;        

Answer 3

As Marc stated you're not constructing instances of myObject when your query is run. But additionally you don't need to cast it to an IQueryable<T>, a LINQ select statment will return an IQueryable<T> unless explicity cast to an IEnumerable<T>.

Also, be careful that your DataContext hasn't been disposed of before you try and access the data being returned. But I noticed your context is not constructed in the method, be careful that you're not maintaining a DataContext for too long, it's a unit-of-work object and not meant to be kept open for long periods of time.

Answer 4

This line is syntactically incorrect:

return ticketDetails.AsQueryable()<myObject>;

and should read

return ticketDetails.AsQueryable<myObject>();

Also, you're creating anonymous objects with the select new {, but you want to create myObject instances. A correct implementation would look like this:

public IQueryable<myObject> getTicketInformation(int ticketID)
{

    return from tickets in _context.tickets
        join file in _context.file_objects on tickets.ticket_id equals file.source_id
        where tickets.ticket_id == ticketID
        select new myObject() { 
            ticket_id = tickets.ticket_id,
            title = tickets.title, 
            care_of_email = tickets.care_of_email, 
            filename = file.filename
        };

}

The new SomeClass() { Property = value, ... syntax creates a SomeClass instance and sets the properties to the given values. Alternatively you could implement a constructor on the myObject class and call it in the linq statement with select new myObject(...).