c# - Operator '!=' cannot be applied to operands of type -

so have controller implementing search file in database. user can optionally filter search 2 fields, organization , category, or can leave dropdown menus "all".

i have 3 tables work with:

(1)

       orgs  --------------------- orgid   |   orgname 

(2)

       cats  --------------------- orgid   |   orgname 

(3)

                   files ------------------------------------------ fileid  |   orgid   |   catid   | filename  

and file name they're searching for. narrow down results, i'm working mirror of files database , deleting rows it:

    [httppost]     public actionresult assetsearch (string selectedorgname, string selectedcatname, string searchval)     {         portaldata pd = new portaldata();          if (selectedorgname != "all")         {              var selectedorgid = pd.orgs.firstordefault(o => o.orgname == selectedorgname); // orgid corresponding selected organization             if (selectedorgid == null) return content("couldn't find row organization '" + selectedorgname + "' in database."); // return error message if no such oranization name exists              (from thisfile in pd.orgs thisfile.orgid != selectedorgid select thisfile).delete(); // delete rows don't have orgid corresponding selected organization          } // if search filtered specific organization          if (selectedcatname != "all")         {              var selectedcatid = pd.cats.firstordefault(c => c.catname == selectedcatname); // catid corresponding selected category              if (selectedcatid == null) return content("couldn't find row category '" + selectedcatname + "' in database."); // return error message if no such organization name exists              (from thisfile in pd.orgs thisfile != selectedcatid select thisfile).delete();          } // if search filtered specfic category  

my first question has error mentioned in title. error pointing

thisfile.orgid != selectedorgid 

and

thisfile.orgid != selectedcatid 

i'm not sure why doesn't expressions, considering orgids in sql database ints , should value returned pd.orgs.firstordefault(o => o.orgname == selectedorgname).

my next question how can make messy code above more compact, efficient, readable , reliable.

(i'm n00b c#/linq/etc., go easy on me!)

var selectedorgid = pd.orgs.firstordefault(o => o.orgname == selectedorgname); 

will of entity type "organisation", not it's id, same

var selectedcatid = pd.cats.firstordefault(c => c.catname == selectedcatname); 

so need select id this:

var selectedorgid = pd.orgs.firstordefault(o => o.orgname == selectedorgname).orgid; 

i'd suggest check null there, result of query

pd.orgs.firstordefault(o => o.orgname == selectedorgname) 

is not null