c# - Changes to entity not registering -

i trying update list in 1 of entities. i'm doing:

var loggedinuserid = user.identity.getuserid(); var applicationdbcontext = new applicationdbcontext();  var x = request["groupcode"]; var affectedgroup = db.studentgroups.firstordefault(s => s.code == x); var groupid = affectedgroup.id; if (affectedgroup != null) {     if (affectedgroup.studentids == null)     {         affectedgroup.studentids = new list<string>();     }     if (affectedgroup.studentids.contains(loggedinuserid))     {         tempdata["errormessage"] = "you member of group";     }     else     {         affectedgroup.studentids.add(loggedinuserid);         db.savechanges();        } } 

here studentgroup model:

public class studentgroup {     public int id { get; set; }     [required(errormessage = "the group must have name.")]     public string name { get; set; }     [required(errormessage = "the code required.")]     public string code { get;set; }     public string description { get; set; }      [display(name="members")]     public ilist<string> studentids { get; set; } } 

the problem studentids null when run in debugger, though when step through it, id added. i'm new asp.net mvc, please bear in mind.

i recommend using cross reference table handle functionality instead. have studentgroup model have id, code, name, , description fields; create xstudentsinstudentgroup table stores studentid , studentgroupid relate two.

the rest of code semi similar. can still groupid same way, once have can pull of student ids xstudentsinstudentgroup , use them however.

if(context.xstudentsinstudentgroup.any(x => groupid == x.studentgroupid &&  x.studentid == loggedinuserid)) {    //already in } else {   var xstudent = new xstudentsinstudengroup()   {     studentid = loggedinuserid     studentgroupid = groupid   };   context.insert(xstudent);//this depends on how add new records   context.savechanges(); } 

i how setting controllers. should have base creates , disposes new database context every action. or using statement clean context stated before.

--edit-- reason don't recommend way doing because doesn't seem make sense save list of ints , have update. if have working in other areas maybe issue have studentids object list of string , not ints.