asp.net mvc - EF Code First - Populating data in Many to Many -

i'm new asp.net mvc , want create simple blog project, therefore have 2 entity posts , categories. each post can belong many categories , each category can belong many posts.

models.cs

public class category {     [key]     public int categoryid { get; set; }     public int? parentid { get; set; }     public virtual category parent { get; set; }     public string title { get; set; }     public string description { get; set; }     public virtual icollection<news> news { get; set; }      public category()     {         news = new list<news>();     } } public class news {     [key]     public int newsid { get; set; }     public string title { get; set; }     public string summary { get; set; }     public string content { get; set; }     public string source { get; set; }     public string sourceurl { get; set; }     public string images { get; set; }     public string password { get; set; }      public datetime createdat { get; set; }     public datetime? modifiedat { get; set; }     public datetime? deletedat { get; set; }     public string createdby { get; set; }     public string deletedby { get; set; }     public virtual publishperiod publishperiodid { get; set; }     public virtual icollection<category> categories { get; set; }      public news()     {         categories = new list<category>();     } 

}

modelsmap.cs

  public class categorymap:entitytypeconfiguration<category>     {         public categorymap()         {             property(one => one.title).hasmaxlength(100).isrequired();             hasoptional(x => x.parent).withmany().hasforeignkey(x => x.parentid);         }     }      public class newsmap:entitytypeconfiguration<news>     {         public newsmap()         {             property(x => x.createdby).hasmaxlength(150);             property(x => x.deletedby).hasmaxlength(150);             property(x => x.title).isrequired().hasmaxlength(150);             property(x => x.summary).isrequired();             property(x => x.content).isrequired().hascolumntype("ntext");             property(x => x.createdat).hascolumntype("datetime");             property(x => x.password).isoptional().hasmaxlength(128);             property(x => x.deletedat).isoptional();             property(x => x.modifiedat).isoptional();             hasmany(x => x.categories).withmany(x => x.news).map(x =>             {                 x.totable("newscategories");                 x.mapleftkey("news_newsid");                 x.maprightkey("category_categoryid");             });         }     } 

and db context

  public dbset<category> categories { get; set; }     public dbset<news> news { get; set; }     public dbset<publishperiod> publishperiod { get; set; }      protected override void onmodelcreating(dbmodelbuilder modelbuilder)     {         base.onmodelcreating(modelbuilder);         modelbuilder.configurations.add(new categorymap());         modelbuilder.configurations.add(new newsmap());         modelbuilder.configurations.add(new publishperiodmap()); 

i have create view posts displays categories in list checkboxs , each checkbox value category's id. how can insert or update posts , keep relation between post , categories.

newscontroller

// // post: /admin/news/create [httppost] public actionresult create(news news, list<string> category) {     viewbag.categories = catrepository.all.orderby(x => x.title);     if (modelstate.isvalid)     {         foreach (var item in category)         {             news.addcategory(catrepository.find(int.parse(item)));         }         news.createdat = datetime.now;         news.createdby = "m.hesabi";         newsrepository.insertorupdate(news);         newsrepository.save();         return redirecttoaction("index");     }     else     {         return view();     } } 

update: created method in news model @dans said , edited controller.

i'd recommend creating method on news class:

public void addcategory(category category) {     categories.add(category);     category.news.add(this); } 

from controller can add each selected category news instance, , add news dbcontext prior calling savechanges. may depend, however, on how repositories make use of context -- in if open own, instead of accessing shared context, might have attach categories news repository's context prior saving. helps...

update

ientitychangetracker error:

it appears if mvcscaffolding uses separate context each repository. mentioned, having separate contexts can lead additional required steps. stands now, categories tracked context while news tracked context b-- detach/attach category entities between 2 contexts, i'd recommended solution change repositories accept shared context through constructors.

i'm assuming instantiating repositories in controller's constructor, rather using dependency injection, modify constructor code following:

mycontext = new yourcontextclass(); catrepository = new categoryrepository(mycontext); newsrepository = new newsrepository(mycontext); 

you have add constructors repositories assign internal context property, , finally, adjust controller dispose of context.

protected override void dispose(bool disposing) {     if (disposing)         mycontext.dispose();      base.dispose(disposing); }