Max function Linq Query - Nullable Int not IEnumerable?

Question

I've been struggling to use the Max function in my LINQ expression. I want to select various properties from multiple SQL tables for the last year (the "max" year). The red squiggly tells me that my int? does not contain a definition for Max and Enumerable.Max (the function I want) requires a receiver type of IEnumerable< int>. I'm completely new to all this stuff, and while I've searched the web, I can't come up with a clear explanation of what I need to do to fix this. I figured it was an SQL table and it would go through the rows as normal SQL queries do.

My code, which I've tried many variations of:

var otherPrograms = (from hm in db.HabitatManagement
                     join svy in db.Survey on hm.SurveyID equals svy.SurveyID
                     join iu in db.InventoryUsers on hm.UserID equals iu.UserID
                     join pt in db.ProgramType on hm.ProgramTypeID equals pt.ProgramTypeID
                     where pt.Program != "State Agency Public Land Programs" 
                     && pt.Program != "State Agency Private Land Programs" 
                     && svy.ReportingYear.Max() 
                     select new
                      {
                          iu.StateID,
                          hm.ProgramTypeID,
                          pt.Program,
                          svy.ReportingYear
                      })
                       .Distinct()
                       .Select(x => new { x.StateID, x.Program, x.ProgramTypeID, x.ReportingYear, DisplayText = x.ReportingYear.ToString() + ", " + x.StateID.ToString() + ", " + x.Program.ToString() })
                       .OrderBy(x => x.StateID);

I have also tried a nested query to achieve the same thing (not sure I even did it right):

&& svy.ReportingYear = (from svy in db.Survey
                     select svy.ReportingYear.Max())

When I look at the definition for the ReportingYear property it looks like so:

public Nullable<int> ReportingYear {get; set;}

I'm pretty sure the issue is that it's not an IEnumerable< int> so how do I make it one without messing with my SQL tables?

Answer 1

Nullable , by definition, represents a value type that can be assigned null . Meaning the property holds a single value, not a Collection .

From your code it looks like you want to get the maximum of a set of years stored in ReportingYear , so you should probably define ReportingYear as some sort of a collection, like List<int> .

public List<int> ReportingYear { get; set; }

And if being nullable is important, create a list of nullable integers , as follows:

public List<int?> NullableReportingYear { get; set; }

Answer 2

Before the where add the following, then use maxYear instead of your svy.ReportingYear.Max()

let maxYear = (from svy in db.Survey
                    where svy.MaxYear != null
                    select (int)svy.MaxYear).Max()

So...

&& svy.ReportingYear.Max() 

Needs to be changed to

&& svy.ReportingYear != null && svy.ReportingYear == maxYear

or

&& (svy.ReportingYear == null || svy.ReportingYear == maxYear)

Answer 3

This should give the max ReportingYear value in the Survey collection/table:

int max = (from svy in db.Survey
                               where svy.ReportingYear.HasValue
                               select svy.ReportingYear.Value).Max();