c# - ViewModel does not update Model correctly on submit -

i trying use strongly-typed viewmodel , find when replace model class viewmodel, changes not submitted correctly edit template. whereas using straight model class in view, edits happen successfully. model class materialdefinition , viewmodel class materialdefinitionviewmodel shown below. i've updated edit template correctly reference viewmodel editing not work. i'm using vs2013 , mvc4. ideas, someone?

first viewmodel class...

public class materialdefinitionviewmodel {     // properties     public materialdefinition definition { get; private set; }      // constructor     public materialdefinitionviewmodel(materialdefinition def)     {         definition = def;     } } 

and code view...

<div class="editor-field">     @html.editorfor(model => model.definition.mddescription)     @html.validationmessagefor(model => model.definition.mddescription) </div>  <p>     <input type="submit" value="save" /> </p> 

finally discovered answer after searching...

    [httppost]     public actionresult edit(string id, formcollection collection)     {         materialdefinition def = repository.getmaterialdefinition(id);         updatemodel(def, "definition");         //updatemodel(def);         repository.save();         return redirecttoaction("details", new { id = def.mdid });     } 

turns out there not-so-obvious overload updatemodel method takes prefix "name" property. name of original encapsulated model class inside viewmodel. corrected code fragment controller's edit post method shown above.