c# - How do I transfer ViewModel data between POST requests in ASP.NET MVC? -

i have viewmodel so:

public class producteditmodel {     public string name { get; set; }     public int categoryid { get; set; }     public selectlist categories { get; set; }      public producteditmodel()     {         var categories = database.getcategories(); // made-up method         categories = new selectlist(categories, "key", "value");     } } 

then have 2 controller methods uses model:

public actionresult create() {     var model = new producteditmodel();     return view(model); }  [httppost] public actionresult create(producteditmodel model) {     if (modelstate.isvalid)     {         // convert model actual entity         var product = mapper.map(model, new product());         database.save(product);         return view("success");     }     else     {         return view(model); // fails     } } 

the first time user goes create view, presented list of categories. however, if fail validation, view sent them, except time categories property null. understandable because modelbinder not persist categories if wasn't in post request. question is, what's best way of keeping categories persisted? can this:

[httppost] public actionresult create(producteditmodel model) {     if (modelstate.isvalid)     {         // convert model actual entity         var product = mapper.map(model, new product());         database.save(product);         return view("success");     }     else     {         // manually populate categories again if validation failed         model.categories = new selectlist(categories, "key", "value");         return view(model); // fails     } } 

but ugly solution. how else can persist it? can't use hidden field because it's collection.

i typically implement lists (for drop downs) readonly property. when view gets value property self contained on needs return values.

public selectlist categories {         {         var categories = database.getcategories(); // made-up method         return new selectlist(categories, "key", "value");     } } 

if necessary can grab selected item (i.e. validation failed) property containing id posted , bound instance of class.