AngularJS checkbox dynamic ng-true-value expression

Question

I'm trying to build a calculator for daycare prices in Angular.

Every location in the company franchise has separate prices for every day. So my thinking was to build a form, with first a select that allows you to select the location, then a series of checkboxes for the days.

I'm having trouble with ng-true-value in the checkboxes selecting the correct prices from my json file.

UPDATE: Added Plunkr: http://plnkr.co/edit/MDmrqaH1VzLBzjd5eHgT?p=preview

Consider this code:

        <p class="kind_section">Choose location</p>
        <select ng-model="formData.location" ng-options="location.title for location in data.bso"></select>

        <p class="kind_section">Select days</p>

        <input type="checkbox" ng-model="location.day.mon" ng-change="calculatePrice()" ng-true-value="{{data.bso[formData.location.ID].prices.monday}}" ng-false-value="0">Ma
        <input type="checkbox" ng-model="location.day.tue" ng-change="calculatePrice()" ng-true-value="{{data.bso[formData.location.ID].prices.tuesday}}" ng-false-value="0">Di<br />
        <input type="checkbox" ng-model="location.day.wed" ng-change="calculatePrice()" ng-true-value="{{data.bso[formData.location.ID].prices.wednesday}}" ng-false-value="0">Wo
        <input type="checkbox" ng-model="location.day.thu" ng-change="calculatePrice()" ng-true-value="{{data.bso[formData.location.ID].prices.thursday}}" ng-false-value="0">Do<br />
        <input type="checkbox" ng-model="location.day.fri" ng-change="calculatePrice()" ng-true-value="{{data.bso[formData.location.ID].prices.friday}}" ng-false-value="0">Vr

First the select sets formData with a location ID, then I want to use this ID to select the day prices for the matching location and set those to ng-true-value.

I'm using ng-true-value="{{data.bso[formData.location.ID].prices.monday}}" for this. This doesn't work.

When I set the ID manually like ng-true-value="{{data.bso[0].prices.monday}}" it does work. Why is the result of the select not being picked up by ng-true-value?

This is my json file:

  $scope.data = {
                "bso": [
                  {
                    "ID": 0,
                    "title": "Locatie 1",
                    "prices": {
                        "monday": 130,
                        "tuesday": 130,
                        "wednesday": 200,
                        "thursday":130,
                        "friday": 130
                    }
                  },
                  {
                    "ID": 1,
                    "title": "Locatie 2",
                    "prices": {
                        "monday": 430,
                        "tuesday": 530,
                        "wednesday": 600,
                        "thursday":990,
                        "friday": 730
                    }
                  }
                ]
              };

Answer 1

It seems ng-true-value does not accept non-constant expressions. From the docs(v1.3.0):

Some attributes used in conjunction with ngModel (such as ngTrueValue or ngFalseValue) will only accept constant expressions.

Examples using constant expressions include:

<input type="checkbox" ng-model="..." ng-true-value="'truthyValue'">
<input type="checkbox" ng-model="..." ng-false-value="0">

Examples of non-constant expressions include:

<input type="checkbox" ng-model="..." ng-true-value="someValue">
<input type="checkbox" ng-model="..." ng-false-value="{foo: someScopeValue}">

An ideal workaround probably would be calling a Controller method on ng-click or ng-change inside which you can analyse all the checkboxes for truthy or non-truthy values.