c# - Entity Framework doesn't recognise methods like Add, Remove -

i working entity framework on asp.net mvc3 visual studio 2010 , have problem: after changed database , moved project 1 computer another, no longer recognize methods of dbcontext such add, remove, , not know how reproduce them.

mention code worked on computer. did not nothing relevant changes on database model.

on following example, db dbcontext , tmsentities name of instance.

public class categorycontroller : controller {         //         // get: /category/         private tmsentities db = new tmsentities();          [httppost]         public actionresult addcategory(category model)         {             bool success = true;             string status = string.empty;             category item = new category();             item.name = model.name.trim();             item.description = model.description;              if (string.isnullorempty(item.name))             {                 success = false;                 status += "category name can not empty! <br />";             }              var duplicate = db.categories.where(a => a.name == item.name).count();              if (duplicate > 0)             {                 success = false;                 status += "name exists! <br />";             }              if (success)             {                 db.categories.add(item);                 db.savechanges();                 return json(new { success = success, status = status });             }             else             {                 return json(new { success = success, status = status });             }         } } 

and after, error such as:

'system.data.objects.objectset' not contain definition 'add' , no extension method 'add' accepting first argument of type

'system.data.objects.objectset' found (are missing using directive or assembly reference?)

instead of using .add() use .addobject() , instead of using .remove use .deleteobject()... beacause

the reason worked because declared context using object content , no dbcontext. dbcontext wrapper on objectcontext. easier use. somehow exercise has mixed 2 up. when creating model , content in place, if teh right project type used , lastest nuget packages in, should t4 (template generates code) uses dbcontext. code above accessing context derived dbcontext. suggest take close @ context def , regenerate it. highly recommend move dbcontext