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up vote 0 down vote favorite

How do I correctly return a list of "CarTypes" objects (from the second method), where the TyreID that is passed in, is not the primary key of the CarType class - so for example, I want to return a list of all CarTypes, where the TyreID is 5:

// GET api/CarTypes
public IEnumerable<CarTypes> GetCarTypes()
{
    return db.CarTypes.AsEnumerable();  //This works fineCar
}

// GET api/CarTypes/5
public IEnumerable<CarTypes> GetCarTypes(long id)
{
    CarTypes cartypes = db.CarTypes.Select(t => t.TyreID == id).AsEnumerable();
    if (roomtypes == null)
    {
        throw new HttpResponseException(Request
            .CreateResponse(HttpStatusCode.NotFound));
    }

    return cartypes;
}

It currently shows the error:

Cannot implicitly convert type 'System.Collections.Generic.IEnumerable' to 'MvcApplication4.Models.CarTypes'. An explicit conversion exists (are you missing a cast?)

And does it matter if I use Select/SelectMany/Where in the query?

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3 Answers 3

up vote 2 down vote accepted

Firstly you need to use Where instead of Select; secondly you don't need to use AsEnumerable() after you've changed it to Where but you might have to call ToList() so that the Linq2Sql/EntityFramework executes the query before returning the values to the view.

 // GET api/CarTypes/5
    public IEnumerable<CarTypes> GetCarTypes(long id)
    {
        var cartypes = db.CarTypes.Where(t => t.TyreID == id).ToList();
        if (cartypes == null || !cartypes.Any())
        {
            throw new HttpResponseException(Request.CreateResponse(HttpStatusCode.NotFound));
        }

        return cartypes;
    }

I've also added in an additional check after the query has executed but you might not need this depending on how you want to handle an empty collection.

share|improve this answer
    
Hi @WestDiscGolf - VS (2012 RC) shows an error on the db.CarTypes... Cannot implicitly convert type 'System.Collections.Generic.List<MvcApplication4.Models.CarTypes>' to 'MvcApplication4.Models.cartypes –  Mark Tait Jun 8 '12 at 11:36
    
Fixed; see edit. Changed the variable declaration to var. –  WestDiscGolf Jun 8 '12 at 13:56
    
thanks a lot. Mark –  Mark Tait Jun 9 '12 at 17:41
up vote 1 down vote

Shouldn't you have:

IEnumerable<CarTypes> cartypes = db.CarTypes.Where(t => t.TyreID == id).AsEnumerable();

Instead of:

CarTypes cartypes = db.CarTypes.Select(t => t.TyreID == id).AsEnumerable();

Note: I would have made this a comment under PanJanek's answer but I'm not currenlty allowed beacuse of my low reputation...

share|improve this answer
    
Thanks a lot - that's what I was missing (IEnumerable at the start of the line) - PanJanek/Mike - thank you also for helping - cheers, Mark –  Mark Tait Jun 8 '12 at 10:43
up vote 0 down vote

You should use "Where" Instead of "Select".

CarTypes cartypes = db.CarTypes.Where(t => t.TyreID == id).AsEnumerable();

"Select" is for specifying which data should be returned for each record, not for filtering the records. Your query with "Select" returns boolean values: false for records with TyreID != id and true for one record where TyreID = id :)

share|improve this answer
    
also, don't you want to return cartypes.AsEnumerable() –  Mike Simmons Jun 8 '12 at 10:18
    
Hi - I do have .AsEnumerable() at the end of the Linq statement - but whether I add cartypes.AsEnumerable() or not, the error still remains on the linq statement. Thanks again, Mark. –  Mark Tait Jun 8 '12 at 10:23

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