How can I set a dynamic model name in AngularJS?

Question

I want to populate a form with some dynamic questions (fiddle here):

<div ng-app ng-controller="QuestionController">
    <ul ng-repeat="question in Questions">
        <li>
            <div>{{question.Text}}</div>
            <select ng-model="Answers['{{question.Name}}']" ng-options="option for option in question.Options">
            </select>
        </li>
    </ul>

    <a ng-click="ShowAnswers()">Submit</a>
</div>
​
function QuestionController($scope) {
    $scope.Answers = {};

    $scope.Questions = [
    {
        "Text": "Gender?",
        "Name": "GenderQuestion",
        "Options": ["Male", "Female"]},
    {
        "Text": "Favorite color?",
        "Name": "ColorQuestion",
        "Options": ["Red", "Blue", "Green"]}
    ];

    $scope.ShowAnswers = function()
    {
        alert($scope.Answers["GenderQuestion"]);
        alert($scope.Answers["{{question.Name}}"]);
    };
}​

Everything works, except the model is literally Answers["{{question.Name}}"], instead of the evaluated Answers["GenderQuestion"]. How can I set that model name dynamically?

Etymologize

Answer 1

http://jsfiddle.net/DrQ77/

You can simply put javascript expression in ng-model.

Dyanna

I swear I tried that. Thank you, very much. I actually went a different route, and just set the model to question.Answer (I'll put out an updated fiddle in a bit), which turned out to be a more direct answer (gotta get out of the jQuery mindset), but it's great to know that I can, indeed, do it the way that I originally planned for the future. Thanks again! – Etymologize

In case this helps anyone else, I was having similar issues, but my problem was that I was using ng-pattern="field.pattern" when what I really wanted was pattern="{{field.pattern}}". Kind of confusing that angular usually provides a helper for dynamic attributes but this time wrote it's own client-side validation and gave it the same name. – Queeniequeenly

Why did you decide to create an empty object (Answers) when you have no actual purpose for it? You seem to be using it only in the ng-model & other than this, there does not seem to be any purpose.So why not omit it altogether and make it work that way? Could you please clarify? – Photomural

I just tried to make a minimum change from the original code. If you look at Mike's revised code(jsfiddle.net/2AwLM/23), he decided to get rid of it. – Dyanna

Thank you SO much for this. Helped me a lot. See here: #34082403 – Caudal

Answer 2

You can use something like this scopeValue[field], but if your field is in another object you will need another solution.

To solve all kind of situations, you can use this directive:

this.app.directive('dynamicModel', ['$compile', '$parse', function ($compile, $parse) {
    return {
        restrict: 'A',
        terminal: true,
        priority: 100000,
        link: function (scope, elem) {
            var name = $parse(elem.attr('dynamic-model'))(scope);
            elem.removeAttr('dynamic-model');
            elem.attr('ng-model', name);
            $compile(elem)(scope);
        }
    };
}]);

Html example:

<input dynamic-model="'scopeValue.' + field" type="text">

Furnivall

Works as expected. – Ragen

Nice. But still wish we could just use ng-model="{{ variable }}" :) – Tribromoethanol

Answer 3

What I ended up doing is something like this:

In the controller:

link: function($scope, $element, $attr) {
  $scope.scope = $scope;  // or $scope.$parent, as needed
  $scope.field = $attr.field = '_suffix';
  $scope.subfield = $attr.sub_node;
  ...

so in the templates I could use totally dynamic names, and not just under a certain hard-coded element (like in your "Answers" case):

<textarea ng-model="scope[field][subfield]"></textarea>

Hope this helps.

Monteux

Answer 4

To make the answer provided by @abourget more complete, the value of scopeValue[field] in the following line of code could be undefined. This would result in an error when setting subfield:

<textarea ng-model="scopeValue[field][subfield]"></textarea>

One way of solving this problem is by adding an attribute ng-focus="nullSafe(field)", so your code would look like the below:

<textarea ng-focus="nullSafe(field)" ng-model="scopeValue[field][subfield]"></textarea>

Then you define nullSafe( field ) in a controller like the below:

$scope.nullSafe = function ( field ) {
  if ( !$scope.scopeValue[field] ) {
    $scope.scopeValue[field] = {};
  }
};

This would guarantee that scopeValue[field] is not undefined before setting any value to scopeValue[field][subfield].

Note: You can't use ng-change="nullSafe(field)" to achieve the same result because ng-change happens after the ng-model has been changed, which would throw an error if scopeValue[field] is undefined.

Maihem

Answer 5

Or you can use

<select [(ngModel)]="Answers[''+question.Name+'']" ng-options="option for option in question.Options">
        </select>

Sullins