c# - textbox data writes back to database, but textboxfor will not -

i'm picking it's best practice use strongly-typed textboxfor helper method rather simple textbox. i'm that. made switch in project, data stopped getting written database. i'm having trouble figuring out why.

here's model.

public class mastermodel {     [key]     public int mandatorykey { get; set; }     public list<tbladdress> address { get; set; }     public list<tblprimarycaregiverdata> primary { get; set; }     public list<tblphone> phone { get; set; }     public list<tblemail> email { get; set; }     public list<tblrelatedcaregiver> related { get; set; }     public list<tbltraininghistorymain> traininghistory { get; set; }     public list<tblinquiryreferralstatu> inquiryreferral { get; set; } } 

then controller

public actionresult create(mastermodel mastermodel)     {         if (modelstate.isvalid)         {              db.tblprimarycaregiverdatas.add(mastermodel.primary[0]);             db.savechanges();              int newcaregiverid = db.tblprimarycaregiverdatas.orderbydescending(p => p.caregiverid)                 .firstordefault().caregiverid;               foreach (var ph in mastermodel.phone)             {                 ph.caregiverid = newcaregiverid;                 db.tblphones.add(ph);             }              db.savechanges();             return redirecttoaction("index");         } 

now, in view (which invokes several partial views, 1 each table in master model), when created fields this:

selectlist phonetypes = viewbag.phonetype; <div>     <label class="label-fixed-width">phone:</label>     @html.textbox("mastermodel.phone[0].phone", null, new { style = "width: 600px" })     @html.dropdownlist("mastermodel.phone[0].phonetype",phonetypes, null, new     {         @class = "form-control-inline dropdown",         style = "width: 100px"     }) 

...i able write data database. when switched on textboxfor this:

selectlist phonetypes = viewbag.phonetype; <div>     <label class="label-fixed-width">phone:</label>     @html.textboxfor(x => x.phone[0].phone, null, new { style = "width: 600px" })     @html.dropdownlistfor(x => x.phone[0].phonetype, phonetypes,"--------", new     {         @class = "form-control-inline dropdown",         style = "width: 100px"     }) 

the phone section of mastermodel empty when post back. can me understand what's going on here?

when post model actionresult , return same view, values model objects contained in modelstate. modelstate contains information valid/invalid fields actual posted values. if want update model value, can this:

 foreach (var ph in mastermodel.phone)             {                modelstate.clear()//added here                 ph.caregiverid = newcaregiverid;                 db.tblphones.add(ph);             }