Question

I have an object with two different integer properties in it, and I’m trying to get a a new object in Linq to Entities, combining two integer properties from the same object as concatenated strings, as follows

List<DateRange> collection = (from d in context.dates 
select new DateRange 
{ 
  DateString = from s in context.Seasons 
  where s.SeasonID = d.DateID 
  select string.Format("{0} - {1}", s.StartYear, s.EndYear) }

).ToList<DateRange>(); 

The string concatenation of the years will not compile.

Answer 1

Assuming you are connecting to a database via LINQ to SQL/Entities, then the String.Format call will likely fail, as with those providers, the select clause is executed within the database. Not everything can be translated from C# into SQL.

To convert your database results into a string like you want to, the following should work:

var temp = (
  from d in context.dates 
  from s in context.Seasons 
  where s.SeasonID == d.DateID 
  select new { s.StartYear, s.EndYear }
).ToList(); // Execute query against database now, before converting date parts to a string

var temp2 = 
  from t in temp 
  select new DateRange 
  { 
    DateString = t.StartYear + " - " + t.EndYear 
  };

List<DateRange> collection = temp2.ToList();

EDIT:
I had an additional thought. The String.Format call is most likely the problem. I am not sure if it would work or not, but what about a plain-jane concat:

List<DateRange> collection = 
(from d in context.dates 
 select new DateRange 
 { 
   DateString = from s in context.Seasons 
   where s.SeasonID = d.DateID 
   select s.StartYear + " - " + s.EndYear
 }
).ToList<DateRange>();