Only parameterless constructors and initializers are supported in LINQ to Entities message

Question

I have a method that returns data from an EF model.

I\'m getting the above message, but I can\'t wotk our how to circumvent the problem.

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Answer 1

It's complaining because it can't convert references to FundedCount to SQL statements.

All LINQ providers convert LINQ statements and expressions to operations that their target can understand. LINQ to SQL and LINQ to EF will convert LINQ to SQL, PLINQ will convert it to Tasks and parallel operations, LINQ to Sharepoint will convert it to CAML etc.

What happens if they can't do the conversion, depends on the provider. Some providers will return intermediate results and convert the rest of the query to a LINQ to Objects query. Others will simply fail with an error message.

Failing with a message is actually a better option when talking to a database. Otherwise the server would have to return all columns to the client when only 1 or 2 would be actually necessary.

In your case you should modify your select to return an anonymous type with the data you want, call ToList() and THEN create the FundedCount objects, eg:

.Select( x=> new {Id=x.Key.BuyerId,Count=x.Count()/30 * daysInMonth)
.ToList()
.Select(y => new FundedCount(y.Id,y.Count))
.ToList();

The first ToList() will force the generation of the SQL statement and execute the query that will return only the data you need. The rest of the query is actually Linq to Objects and will get the data and create the final objects