c# - populate many-to-many relationship table using navigation properties in Entity Framework -

i learning entity framework in asp.net mvc application. have 3 models -

appmodel, categorymodel , app_categorymodel (to specify many many relationship between appmodel , categorymodel). snippet of is:

public class categorymodel     {         [key]         public int id { get; set; }         public string name {get; set; }         public virtual icollection<app_categorymodel> mapping { get; set; }     }      public class appmodel     {         [key]         public int id { get; set; }         public string name { get; set; }         public virtual icollection<app_categorymodel> mapping { get; set; }     }      public class app_categorymodel     {         [key]         public int id {get; set;}          public int appid {get; set; }         public int categoryid {get; set; }          public virtual appmodel app {get; set;}         public virtual categorymodel category {get; set;}     } 

i following 'code-first' approach , tables got created successfully. but, stuck @ how populate , display information. have following input data: list<appmodel> list<categorymodel> , dictionary<"appname", list<categorymodel>>

how move on here can update mapping table?

also, wanted understand whether correct approach represent data. since app can have multiple categories - expect output collection of unique apps along list of categories each app, like:

dictionary<appmodel, list<categorymodel>> 

edit: tried per suggestion smoksnes-

    list<categorymodel> cat_list = new list<categorymodel>();     categorymodel c1 = new categorymodel();     c1.name = "string1";     cat_list.add(c1);      categorymodel c2 = new categorymodel();     c2.name = "string2";     cat_list.add(c2);      list<appmodel> app_list = new list<appmodel>();     appmodel a1 = new appmodel();     a1.name = "app1";     app_list.add(a1);      appmodel a2 = new appmodel();     a2.name = "app2";     app_list.add(a2);      a1.mapping.add(c1);     a1.mapping.add(c2);     a2.mapping.add(c1);     a2.mapping.add(c2);      db.categories.addrange(cat_list);     db.apps.addrange(app_list);      db.savechanges(); 

after this, ef worked expeted - 2 categories , 2 apps , 4 entries in mapping table.

although worked, not sure stopping ef create 4 entries categories?

just barry o´kane mentioned in comment there's no reason keep app_categorymodel model. ef manage you. should keep if contains information regarding relation between 2 tables. according example, there's no reason keep it.

public class categorymodel {     public categorymodel()     {         appmodels = new list<appmodel>();     }      [key]     public int id { get; set; }     public string name {get; set; }     public virtual icollection<appmodel> appmodels { get; set; } }  public class appmodel {     public appmodel()     {         // not sure if needed anymore. ef adds it.         categorymodels = new list<categorymodel>();     }      [key]     public int id { get; set; }     public string name { get; set; }     public virtual icollection<categorymodel> categorymodels { get; set; } } 

and regarding question representation, don't think it's necessary. since appmodel has connected categorymodel on it's model there's no reason dictionary. can store in list<appmodel> instead.

ilist<appmodel> myapps = context.appmodels.tolist();  foreach (var myapp in myapps) {     console.writeline("app {0} has following categories:", myapp.id);     foreach (var category in myapp.categorymodels)     {         console.writeline(category.name);     } } 

and when want add category app:

// don't know how create context, below it's called context. var newcategorymodel = new categorymodel {     name = "so awesome!" }; var appmodel = context.appmodels.firstordefault(x => x.id == 1); appmodel.categorymodels.add(newcategorymodel); // ef automatically set foreign keys you... context.savechanges(); 

and if want make sure no category added twice:

public void addcategory(int appid, string categoryname) {     using(var context = new dbcontext())     {         var category = context.categorymodels.firstordefault(x => x.name == categoryname);         if(category == null)         {             // create new categorymodel if doesn't exist.             category = new categorymodel             {                 name = categoryname             };         }         var appmodel = new appmodel         {             id = appid         };         // attach save on db-trip         context.appmodels.attach(appmodel);          //todo: possibly check if particular appmodel has category?         appmodel.categorymodels.add(category);         context.savechanges();     } }