Enhance Select Dropdown in AngularJS with Grouping and Default Selection

I am facing an issue with a form that includes a SELECT element. I have successfully loaded the possible values in my controller from a function that retrieves data from a database and groups the options by a group name.

Although the list of options is loading properly with the grouping displayed, the initial value is not showing up - which is based on a data model. It appears blank initially, but when I select any option from the list, it displays correctly.

I have followed an example from a solution Populate a Dropdown list by grouping using AngularJs, and according to other examples I have seen, this should work. I suspect there might be a minor detail that I have overlooked accidentally.

The following code loads the potential values for the drop-down:

$http.get("api/getIndustry").success(function(data){
    $rootScope.industryData = [];
    $.each(data, function (i, data) {
        $rootScope.industryData.push({
            group: data.group,
            id: data.id, 
            text:  data.text
        });
    });                      
});

Currently, I am trying to set an initial selected value (which will eventually come from reading a record):

$scope.example3model = {group: 'Energy and Natural Resources', id: '25', text: 'Utilities'};

Below is a snippet of my view:

<td colspan="4" ng-hide="editableForm.$visible">
    <select ng-model="example3model" class="form-control input-md" ng-options="industry.text group by industry.group for industry in industryData" >
    </select></br>
    {{example3model}}    <- checking what was chosen
</td>

I am unsure about what else I can do to make this work. The only issue I see at this moment is that the list does not display the 'default' value of what is initially in example3model (resulting in a blank list). However, if I choose a value from the list, it shows correctly.

Any tips or suggestions would be greatly appreciated.

Answer №1

The issue arises when attempting to assign the initial value to an object literal, which may appear identical to one within the select options but is not actually the same.

This discrepancy stems from how Javascript and AngularJS handle setting that initial object-value (not a problem if options were an array of primitives like numbers or strings): {} and {} may look alike to us, but in JS they are distinct entities. To illustrate this, try running a comparison in the browser console:

{} == {}
// returns false
{ a: 1 } == { a: 1 }
// also returns false

Under the hood, Angular checks if the ngModel corresponds with any reference within the ngOptions, highlighting the importance of referencing the initial value directly from the options array.

In your case, the initialization should follow a pattern similar to this specific example provided (keeping in mind that I am setting the id to match your scenario, but it can be adjusted accordingly):

const defaultId = 25;
$scope.example3model = $rootScope.industryData.find(data => +data.id === defaultId)

Now, the ngModel points to the desired object within the referenced array.

* Refer to the official documentation for insights on handling complex models with ngOptions

[Please note that this approach may fail if none of the objects in the ngOptions array matches the defaulted id]

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