CODEWITHSUNDEEP
c#linqlambda
Matt M.
Matt M.

Reputation: 822

Pass a lambda as a variable to a .Select()

I want to pass a lambda to my .Select() method depending on a condition.

I set my lambda up like this:

Func<Monthly, int?> f = x => x.CLDD;

I then set up my .Select() like this:

IQueryable query =
 db.Monthlies
 .GroupBy(o => o.Date.Value.Year)
 .Select(
   o => new {
     Year = o.Key,
     MaxDate = o.Max(x => x.Date),
     Data = o.Sum(f)
   }
 )
 .Where(o => o.Year != currentYear)
 .OrderBy(o => o.Year);

The code compiles and runs fine but the query does not send back any results. When I debug and watch query I see it says:

+ base {"Internal .NET Framework Data Provider error 1025."}
System.SystemException {System.InvalidOperationException}

Note if instead I do:

Expression<Func<Monthly, int?>> f = x => x.CLDD;

Then o.Sum(f) errors saying:

Error   1   Instance argument: cannot convert from 
'System.Linq.IGrouping<int,MyWeb.Models.Monthly>' to
System.Linq.IQueryable<MyWeb.Models.Monthly>'

Thank you!

Upvotes: 0

Views: 648

Answers (1)

Diego
Diego

Reputation: 20194

You were close, Entity Framework needs an Expression to work not Func, but the Sum extension method that receives an Expression works only with IQueryable.

Now inside Select you are getting an IGrouping from GroupBy which does not implement IQueryable only IEnumerable.

So you just need to cast it to get the right extension method:

Data = o.AsQueryable().Sum(f)

Upvotes: 2

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