How to convert an 'int' data type item to 'string' and search in a string list using 'Contains' in LINQ?

Question

I am working on a project which uses ASP.net web forms and C# entity framework using LINQ. I am retrieving an 'int' type data list from one function and Check it in another string list using 'Contains'. There I have used

'SqlFunctions.StringConvert((double)MY_INT_ITEM).Trim()'

to convert that int type item (ID) to the string. It worked before but now I forget how I did it. Now when I am trying to do that it gives the following error,

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"Unable to cast the type 'System. Nullable`1' to type 'System.Object'. LINQ to Entities only supports casting EDM primitive or enumeration types."

Why am I getting this error and how can I fix that? Here I have attached my code. Thank you.

public static List<SESAssignmentsType> getNotUplodedUnitDetailsList(List<string> possibleUnits)
    {
        using (SESEntities db = new SESEntities())
        {
            var properUnitList = (from s in db.SES_SCHEDULE_LECTURE
                                  join u in db.SES_UNDERGRADUATE_UNIT_DETAILS on s.SCH_UNIT_ID equals u.ID
                                  where possibleUnits.Contains(SqlFunctions.StringConvert((double)s.ID).Trim())
                                  select new SESAssignmentsType
                                  {
                                      ID = s.ID,
                                      UNIT_NAME = u.UND_UNIT_NAME + " - " + a.SCH_START_DATE + " - " + a.SCH_START_TIME+ " ( Started " +
                                              SqlFunctions.DateName("day", a.SCH_START_DATE) + "/" + SqlFunctions.StringConvert((double)a.SCH_START_DATE.Value.Month).TrimStart() + "/" + SqlFunctions.DateName("year", a.SCH_START_DATE)


                                  }).ToList();


            return properUnitList;
        }
    }

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Thank you very much for your help. Finally, I found the issue it is because some of the values concatenated in UNIT_NAME is nullable. @Rahul Sharma thank you very much for your idea to check nullable.

Answer 1

Check this after convert S.ID in to string in contains use like this below example possibleUnits.Contains(s.ID.ToString())

Answer 2

It looks for me that s.ID is a nullable, which means you should change it to this:

where possibleUnits.Contains(SqlFunctions.StringConvert((double)s.ID.Value).Trim())

Note that this doesnt check if s.ID is null, so you need to do that by yourself.