Linq woes - A CollectionType is required

Question

Why doesn't my linq query work?

I suspect it may have something to do with lazy loading. It seems to work in linqpad.

public IList<PaymentDto> GetDocumentPayments(int documentId, bool? allowRepeatPayments, byte[] paymentStatuses, int[] paymentMethods)
    {
        using (var ctx = ObjectContextManager<MyDataContext>.GetManager("MyDataContext"))
        {
            var payments = new List<PaymentDto>();

            var ps = new List<byte>();        
            if (paymentStatuses != null)
            {
                ps = paymentStatuses.ToList();
            }

            var pm = new List<int>();
            if (paymentMethods != null)
            {
                pm = paymentMethods.ToList();
            }

            IQueryable<Payment> data = 
                   from payment in ctx.ObjectContext.Documents.OfType<Payment>()
                   where
                       ps.Contains(payment.Status) && 
                       pm.Contains(payment.Method) &&
                       payment.DocumentId == documentId &&
                       (allowRepeatPayments == null || payment.AllowRepeatPayments == allowRepeatPayments)
                   orderby payment.Id
                   select payment;

            foreach (var p in data) // Fails here
            {
                payments.Add(ReadData(p));
            }

            return payments;
        }
    }

Throws error: A CollectionType is required. Parameter name: collectionType.

Throws an error on what? What's the full exception? What line is it referring to? What's the ReadData() method doing? etc. — Jeff Mercado
See "Fails here" comment in the code. ReadData is just a property copier. :) — Kev

Gert Arnold Gert Arnold · Accepted Answer · 2012-06-29T17:36:43

Constructs like (allowRepeatPayments == null || payment.AllowRepeatPayments == allowRepeatPayments) can do funny thing to a query. Try what happens when you do:

if (allowRepeatPayments.HasValue)
{
    data = data.Where(p => p.AllowRepeatPayments == allowRepeatPayments);
}

You can do the same for paymentStatuses and paymentMethods.

It may solve your problem, but if not, it is an improvement anyway, because the condition is only added when it is necessary and the SQL is not cluttered when it isn't.

Linq woes - A CollectionType is required

2 Answers