Question

I am using LINQ to create a list. But I want to use a function at the end to generate the object iself, something LINQ complains about

LINQ to Entities does not recognize the method 'WashroomStatusItem GetWashroomStatusForItem(WashroomStatus)' method, and this method cannot be translated into a store expression.

What am I doing wrong?

var query = (from c in context.WashroomStatus
    where c.WashroomId == GroupItem.WashroomID
    select GetWashroomStatusForItem(c));

private WashroomStatusItem GetWashroomStatusForItem(WashroomStatus item)
{
    WashroomStatusItem temp = new WashroomMonitorWCF.WashroomStatusItem();
    //do stuff with it
    return temp;
}

Answer 1

The problem is that the SQL conversion can’t convert your method into SQL. You should use AsEnumerable() to “switch” from the out-of-process provider to LINQ to Objects. For example:

var query = context.WashroomStatus
                   .Where(c => c.WashroomId == GroupItem.WashroomID)
                   .AsEnumerable()
                   .Select(c => GetWashroomStatusForItem(c));

Note that if GetWashroomStatusForItem only uses some properties, you may want to project to those separately first, to reduce the amount of information fetched from the server:

var query = context.WashroomStatus
                   .Where(c => c.WashroomId == GroupItem.WashroomID)
                   .Select(c => new { c.Location, c.Date };
                   .AsEnumerable()
                   .Select(p => GetWashroomStatusForItem(p.Location, p.Date));