How to properly implement a drop-down box using <SelectListItem> and repository pattern in ASP.NET MVC -

i know how implement drop-down box using <selectlistitem> type in asp.net mvc. have not used method before, , i've been advised best way go if have perform 'required' validation on drop-down.

i've created drop-down using viewbag, , don't think find approach effective.

my example here simple. small app allows user enter customer name , choose country drop-down. should check user selects country , enters value in name textbox. please have @ code below. incomplete , template, please me how implement approach. please feel free use repository if using effective. i'm still struggling understand how use repository pattern, , explanation needed on well. thanks

customer view model

public class customer {     public int id { get; set; }     [required]     public string name { get; set; }     [required]     public country countryid { get; set; } }  public class country  {     public int countryid { get; set; }     public ienumerable<selectlistitem> countries { get; set; }  } 

model

1. customers - entityframework entity containing table customer details holding foreign key countries entity
2. countries - entity containing table countryid , countryname

action result

models.efentities ctx = new models.efentities();  public actionresult getcustomers() {     using(ctx)      {         need code implement part      }         return view("customers"); } [httppost] public actionresult addcustomer(model.customer customer) {     using(ctx)      {         //i'm thinking of calling savechanges() method on customers entity,          //but please let me know if have better ways of writing code.         // using repository pattern)     }     return view(); } 

customers view view displays simple interface enter customer name , select country dorp-down. i'm thinking should 1 below

@model models.customer  @html.editorfor(model=>model.name) @html.validationfor(model=>model.name) @html.dropdownlistfor(model => model.country..?..need code here well, "please select") @html.validationfor(...need code here make sure user selects country) 

include select list in customer

public class customer {     public int id { get; set; }      [required]     public string name { get; set; }      [required]     public int countryid { get; set; }      public ienumerable<selectlistitem> countries { get; set; }  } 

build model in controller this:

public actionresult getcustomers() {     var model = new customer();     using(ctx)      {         // need code implement part          // > assume know how this, like:         var customer = ctx.customers.get(the_id);         // map entity model         model.id = customer.id;         // map rest of fields here (you may want use mapper tools)          // country list db , map selectlistitem         model.countries = mapcountries(ctx.countries.getall());     }     return view(model); } 

your view

@model models.customer  @html.editorfor(model=>model.name) @html.validationfor(model=>model.name) // implement rest of fields @html.dropdownlistfor(model => model.countryid, model.countries, "please select") @html.validationfor(model => model.countryid) 

then in post method

1. make sure model valid (server-side validation)
2. map model entity
3. save entity database

that's it, need fill in blanks codes specific project.