c# - Except() and Intersect() doesn't work correctly - LINQ -

this question has answer here:

• using linq except not working thought 3 answers

i not sure why not working correctly. possibly because trying use expressions on data class instead of single field in class?

adminonlygroups supposed return groups admin has , user doesn't returning of admin groups

useronlygroups doing same, returning of user groups

commongroups supposed return groups have in common there 2 of, returning null or empty

data class

[datacontract] public class investigatorgroupdata {      [datamember]     public int investigatorgroupid { get; set; }      [datamember]     public string investigatorgroupname { get; set; }  } 

snippet of controller

ienumerable<investigatorgroupdata> admingroups = proxy.getinvestigatorgroups(adminid); ienumerable<investigatorgroupdata> usergroups = proxy.getinvestigatorgroups(userid);  // groups admin has , user doesn't. these enabled , unselected ienumerable<investigatorgroupdata> adminonlygroups = admingroups.except(usergroups);  // groups user has , admin doesn't. these disabled , selected ienumerable<investigatorgroupdata> useronlygroups = usergroups.except(admingroups);  // groups in common. these enabled , selected ienumerable<investigatorgroupdata> commongroups = admingroups.intersect(usergroups);  if (commongroups.isnullorempty()) {     return view("error"); } 

you need implement equality comparer objects

this has been answered before here using linq except not working thought

please see blog post below msdn further explanation http://blogs.msdn.com/b/csharpfaq/archive/2009/03/25/how-to-use-linq-methods-to-compare-objects-of-custom-types.aspx

if anonymous types work differently without equality comparer. here example code

http://odetocode.com/blogs/scott/archive/2008/03/25/and-equality-for-all-anonymous-types.aspx