Question

I have a LINQ to SQL query which produces an object of type {System.Data.Linq.DataQuery}. My problem is I am getting an exception when trying to determine if the list is empty (or null).

I tried various different tests, and searched through StackOverflow for an answer but nothing I tried will get me past this exception:

  // I try to declare explicitly:
   IQueryable<DataAccess.Entities.CompanyProfile> carrierCodes = null;


  // and implicitly
         var carrierCodes = from cc in context.CompanyProfiles
                          where cc.ProfileTypeID == 9 &&
                                cc.CompanyProfileCode == shipTEntity.CargoControlNum.Substring(0, 3) &&
                                cc.CompanyProfileID == shipTEntity.CompanyProfile.CompanyProfileID
                          select cc;



        // VAROIUS NULL REF TESTS
        var _info = carrierCodes.FirstOrDefault( u => u != null); // fails

        int itemCount = Enumerable.Cast<string>(carrierCodes.DefaultIfEmpty()).Count(); // fails

       var InstanceCount = carrierCodes.Count(i => i != null); // fails

        foreach (var companyProfile in carrierCodes) // fails
        {
            if ( companyProfile != null )
                itemCount++;
        }

        var  exists = carrierCodes.DefaultIfEmpty().ToList(); // fails

        int count = exists.Count;

        return count > 0;

As you can see, I tried FirstOrDefault, testing for null (if carrierCodes != null) but that evaluates to false every time. I tried to get the instance count various ways, but since the list is null it gives me an exception when trying to test the count.

What is confusing is that the carrierCode list is not null, but it gives a Object Null reference exception.

PS This is the exception:

 "Object reference not set to an instance of an object."

Thank you,

Confused in Seattle.

UPDATE

I’ve tried the following suggestions – they all produce the same exception as before. I’ve attached the exception dialog and exception details:

  var carrierCodes = from cc in context.CompanyProfiles
                           where cc.ProfileTypeID == 9 &&
                                 cc.CompanyProfileCode == shipTEntity.CargoControlNum.Substring( 0, 3 ) &&
                                 cc.CompanyProfileID == shipTEntity.CompanyProfile.CompanyProfileID
                           select cc;

         // the below all throw ex:
        var isValid = carrierCodes.Count() == 0;
        var isNull  = carrierCodes.FirstOrDefault() == null;

        if ( carrierCodes.ToList().Count == 0 )
        {
            //Don't try to access members of carrierCodes
        }

Exception:

Updated Code:

     var code      = shipTEntity.CargoControlNum.Substring(0, 3);
        var profileId = shipTEntity.CompanyProfile.CompanyProfileID;

        var profiles = from cc in context.CompanyProfiles
                       where cc.ProfileTypeID == 9
                       select cc;

        var codesInProfiles = from p in profiles
                              where p.CompanyProfileCode == code
                              select p;

        var carrierCodes = from c in codesInProfiles
                        where c.CompanyProfileID == profileId
                        select c;

        //var carrierCodes = from cc in context.CompanyProfiles
        //                   where cc.ProfileTypeID == 9 &&
        //                         cc.CompanyProfileCode == shipTEntity.CargoControlNum.Substring( 0, 3 ) &&
        //                         cc.CompanyProfileID == shipTEntity.CompanyProfile.CompanyProfileID
        //                   select cc;

        if ( !profiles.Any() )
            return false;

        if ( !codesInProfiles.Any() )
            return false;

        if ( !carrierCodes.Any() )
            return false;

Answer: the problem was my profile Id was null. .Any() is a good substitute for Count() == 0 btw

Answer 1

As per my original comment, I would guess that one of the used related entities on shipTEntity is not pre-loaded. Probably it’s CompanyProfile in particular.

To resolve this, when retrieving shipTEntity from the data context, you should set some DataLoadOptions.LoadsWith on the context to ensure that it’s related entities are also loaded from the context.