CODEWITHSUNDEEP
c#entity-frameworklinqlinq-to-entities
ca9163d9
ca9163d9

Reputation: 29209

DbExpressionBinding requires an input expression with a collection ResultType

I want to group the table by a column and get the counts, then create dictionary using the result. The last statement returns the error of

DbExpressionBinding requires an input expression with a collection ResultType.

What the error means?

var a = context.Table;
var b = a.GroupBy(x => x.RecordType, (k, cnt) => new { RecType = k, cnt = k.Count() });
var c = b.Select(x => 
    new KeyValuePair<string, Tuple<Type, int>>(
        x.RecType, Tuple.Create(ObjTypes[x.RecType], x.cnt)))
    .ToDictionary(x => x.Key, x => x.Value);

Upvotes: 3

Views: 6185

Answers (1)

Steve Ruble
Steve Ruble

Reputation: 3905

Your GroupBy call is slightly wrong - it's ignoring the cnt parameter. It should be written like this:

var b = a.GroupBy(x => x.RecordType, (k, cnt) => new { RecType = k, cnt = cnt.Count() });

That exception message is one of the more unhelpful I've seen. The problem is that when you call Count on RecordType (aliased as k) in the C# expression it compiles fine, because string implements IEnumerable<char>. Unfortunately, when EF tries to convert that expression to SQL it needs to be able to use the SQL count operator, which can't work on a string - it needs to operate over a sequence of rows. This results in the somewhat cryptic exception you received.

Incidentally, the query assigned to c won't work either - Tuple.Create can't be translated into SQL, nor can ObjTypes[x.RecType]. You'll need to call ToList on variable b before you can do all that additional shaping of your results.

Upvotes: 4

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