c# - Model Validation on collection with checkbox fails when checkbox not rendered -

when index view display 2 people , none of them selected model validation works correctly due minlengthattribute in .net 4.5.

now comes custom logic in ui. when 1 person displayed in index view need no checkbox check it. customer can directly press submit button. try manually fill selectedids array see @else clause.

but code: model.selectedids = new int[]{ item.personid};

does not work, viewmodel.selectedids property on server side action {int[0]}

how can still assign 1 person id selectedids array?

view

   @model listtest.models.peoplelistviewmodel   @{     var hasmorethanoneperson = @model.people.count > 1;    }  @html.beginform("save", "home") {  @html.validationsummary(false)  <table>     @foreach (var item in model.people)     {         <tr>             @if (hasmorethanoneperson)             {                 <td>                     <input type="checkbox" name="selectedids" value="@item.personid" />                 </td>             }             else             {                 model.selectedids = new int[]{ item.personid};             }              <td>                 <input type="text" value="@item.name" />             </td>         </tr>     } </table> <input type="submit" value="save" /> } 

viewmodel

public class peoplelistviewmodel     {         public peoplelistviewmodel()         {             selectedids = new int[] { };         }          [minlength(1, errormessage = "minimum 1 person must selected!")]         public int[] selectedids { get; set; }          public list<person> people { get; set; }     } 

controller

public actionresult index() {      var people = new list<person> {         new person { name = "horst", personid = 10 },          new person { name = "michael", personid = 20}      };      return view(new peoplelistviewmodel { people = people }); }  [httppost] public actionresult save(peoplelistviewmodel viewmodel) {      if (modelstate.isvalid)     {       }      viewmodel.people = new list<person> { new person { name = "horst", personid = 10 }, new person { name = "bernarnd", personid = 20 } };      return view("index", viewmodel); } 

you might consider rendering hidden field in case ensure value sent server:

@if (hasmorethanoneperson) {     <td>         <input type="checkbox" name="selectedids" value="@item.personid" />     </td> } else {     @html.hidden("selectedids", item.personid) } 

but better approach handle on server - means if there's no value assigned in view model fetch backend because user didn't have chance modify value in ui since there no corresponding input element manipulate.