Trigger validation of a field when another field is changed

After searching a lot for this I've found that we can trigger validation simply by calling $validate() on the desired field.
So for example if your form is named my_form (i.e. in the markup the form tag has a name="my_form" attribute) and the name of the field you want to validate is date (in the markup the input field has a name="date" attribute), then as you suggested you can use the ng-change event of the second field and call $scope.my_form.date.$validate(); whenever the ng-change function is invoked.

I had a similar problem: two form fields "interval" (for $scope.monitor.interval) and "timeout" (for $scope.monitor.timeout) with the condition that timeout must not exceed half of interval.

First, I added a custom validator to timeout that checks for this condition. Now I needed to trigger the timeout validator also when interval changes. I achieved this by watching the monitor.interval property of the model:

function EditMonitorCtrl($scope, $log, dialog, monitor) {    $scope.monitor = monitor;    ...    // trigger validation of timeout field when interval changes    $scope.$watch("monitor.interval", function() {        if ($scope.editMonitorDlg.timeout.$viewValue) {                      $scope.editMonitorDlg.timeout.$setViewValue($scope.editMonitorDlg.timeout.$viewValue);        }    });}

Without "if" the timeout value got removed during intialisation of the dialog.

I was unable to get ng-blur="myForm.myField.$validate()" working in AngularJS 1.5, possibly because the model for myField was empty.

However, ng-blur="myForm.myField.$setTouched()" did work.