angularjs - How to trigger binding of select based on the changed value in another select? -

let's have list of countries , each country has list of states/regions. there 2 selects. first select country, , when country changes want trigger binding of states select. how link these 2 controls trigger binding of states select when country changes?

<select id="countries"  data-ng-model="vm.permanentaddress.countrycode"    data-ng-options="country.code country in vm.form.countries">   </select>  <select data-ng-model="vm.permanentaddress.statecode"      data-ng-options="state.value state in vm.getstatesforcountry(vm.permamentaddress.countrycode)"> </select> 

update: not explicit in question want do. not want create new properties watched angular change. want tell anuglar, hey has changed, go ahead , re-evaluate binding control.

is not possible?

in controller have this:

$scope.setstateoptions = function(country){    $scope.stateoptions = /* whatever code use states */  } 

then html can be:

<select id="countries"     data-ng-model="vm.permanentaddress.countrycode"    data-ng-options="country.code country in vm.form.countries"    data-ng-change="setstateoptions(country)">   </select>  <select      data-ng-model="vm.permanentaddress.statecode"      data-ng-options="state.value state in stateoptions"> </select>