Why Angular ng-options with 'track by' can't selected by id

Question

I have a array of objects that I\'m displaying using ng-options, and set ng-model with id. If i add track by on it, the item can\'t selected, if not add, it wor

Answer 1

This Is basically how track by work. track by can only work with object not with any property of the object. and without track by it will work with a separate property not with entire object. Check the code part.

Some lines from Angular js track by (read it for better understanding)

This will work:

  $scope.selected = $scope.items[0];

but this will not work:

 $scope.selected = $scope.items[0].subItem;

angular.module('myApp', [])
  .controller('MyController', ['$scope', function ($scope) {
    $scope.countryList = [{id: 1, name: 'China'}, {id: 2, name: 'America'}, {id: 3, name: 'England'}]
    $scope.country = {id: 1, name: 'China'};
   $scope.countryID = 1;
  }]);

  

     
  
 no track by
{{country}}
   
 have track by, can't selected by id
{{country}}


 no track by
{{countryID}}
   
 have track by, can't selected by id
{{countryID}}