AngularJS : 2-way binding broke when creating new child scope in directive - angularjs

Question

I am using custom angular form validation to validate fields based off the field having a value AND the selected value of a drop down. I use the same section of code (and therefore the same directive) twice on the page. So I could do this re-use, I tried sending in an argument to the directive. This is all working fine. However when the child scope is created it breaks my 2-way binding back to fruit.cost.
Here is an example fiddle.
What am I doing wrong? I want all the validation to work the same but also preserve the 2-way binding. Here is a copy of my fiddle code:
JS
function MainCtrl($scope){
$scope.localFruits = [
{name: 'banana'},
{name: 'orange'},
{name: 'grape'}
];
$scope.fruits = [
{name: 'banana'},
{name: 'orange'},
{name: 'grape'}
];
$scope.costRequired = [
'local',
'overseas'
];
$scope.selectedCostRequired = '';
}
angular.module('test', []).directive('customRequired', function() {
return {
restrict: 'A',
require: 'ngModel',
scope: {
requiredWhenKey: '=',
cost: '=' // I think the problem is here?? Can't figure out how to pass the property I want to bind to
},
link: function(scope, elem, attrs, ctrl) {
//console.log(scope);
function isValid(value) {
if (scope.$parent.selectedCostRequired === scope.requiredWhenKey) {
return !!value;
}
return true;
}
ctrl.$parsers.unshift(function(value) {
var valid = isValid(value);
scope.$parent.subForm.cost.$setValidity('customRequired', valid);
return valid ? value : undefined;
});
ctrl.$formatters.unshift(function(value) {
scope.$parent.subForm.cost.$setValidity('customRequired', isValid(value));
return value;
});
scope.$watch('$parent.$parent.selectedCostRequired', function() {
scope.$parent.subForm.cost.$setValidity('customRequired', isValid(ctrl.$modelValue));
});
}
};
});
HTML
<div ng-app="test" ng-controller="MainCtrl">
<form name="form">
Which grouping is required? <select name="costRequired" ng-model="selectedCostRequired" ng-options="t for t in costRequired"></select>
<h2>Local</h2>
<div ng-repeat="fruit in localFruits" ng-form="subForm">
{{fruit.name}}: <input name="cost" ng-model="fruit.cost" required-when-key="'local'" custom-required/> bound value is: [{{fruit.cost}}]
<span class="error" ng-show="subForm.cost.$error.customRequired">Required</span>
</div>
<h2>Overseas</h2>
<div ng-repeat="fruit in fruits" ng-form="subForm">
{{fruit.name}}: <input name="cost" ng-model="fruit.cost" required-when-key="'overseas'" custom-required/> bound value is: [{{fruit.cost}}]
<span class="error" ng-show="subForm.cost.$error.customRequired">Required</span>
</div>
<div ng-show="form.$invalid" class="error">some form error(s) still exist</div>
<div ng-show="!form.$invalid" class="okay">form looks good!</div>
</form>
</div>

Answer 1

Using ng-model with a directive that creates an isolate scope on the same element doesn't work.
I suggest either not creating a new scope, or use scope: true.
Here is a simplified example that does not create a new scope:
<form name="form">
<div ng-repeat="fruit in localFruits">
{{fruit.name}}:
<input ng-model="fruit.cost" required-when-key="local" custom-required/>
bound value is: [{{fruit.cost}}]
</div>
</form>
function MyCtrl($scope) {
$scope.localFruits = [
{name: 'banana'},
];
}
app.directive('customRequired', function() {
return {
restrict: 'A',
require: 'ngModel',
link: function(scope, elem, attrs, ctrl) {
console.log(attrs.requiredWhenKey);
}
};
});
fiddle
Since the required-when-key attribute is just a string, you can get the value using attrs.requiredWhenKey.
If you don't create a new scope, you should also be able to remove most of the $parent lookups in your directive.