Designing Angular custom form validations (multiple fields) generated by ngRepeat

I would like some feedback on improving/designing custom form validations(multiple fields) the Angular way.

I have some form input fields that are generated by ngRepeat. Basically, the next input must be greater than the the previous. I called these fields beginLevel.

My current implementation is as follow: I am using ngBlur to call a controller function. This function loops through my model comparing the index[i].beginsAtLevel with index[i-1].beginsAtLevel. In the event that the current beginsAtLevel is less than that the previous beginsAtLevel I grab the id of the form-group e.g.

previousIndex = angular.element(document.querySelector('#beginsAtLevel' + (i - 1))); and

currentIndex = angular.element(document.querySelector('#beginsAtLevel' + i));.

I subsequently, add the has-error class to the input fields.

previousIndex.addClass('has-error'); currentIndex.addClass('has-error');

I also have another function removeErrors(), which loops through my model and removes the has-error class.

This approach works but I feel its a bit of a hack. How could I implement/improve this using a directive? I have seen plenty of examples online that validate only one input at a time.

Here is my function for reference:

function validateTiersBeginLevel(tiers) {
    var previous, current, previousIndex, currentIndex;

    for (var i = 1; i < tiers.length; i++) {
        previous = tiers[i - 1].beginsAtLevel;
        current = tiers[i].beginsAtLevel;

        if (Number(current) <= Number(previous)) {

            previousIndex =
                angular.element(document.querySelector('#beginsAtLevel' + (i - 1)));
            currentIndex =
                angular.element(document.querySelector('#beginsAtLevel' + i));
            previousIndex.addClass('has-error');
            currentIndex.addClass('has-error');
        } else {
            clearErrors(tiers);
        }
    }
}

as well as my input field(s) generated by ngRepeat:

<div class="form-group" 
    ng-class="{'has-error': tierForm.beginsAtLevel{{$index}}.$touched &&  
        tierForm.beginsAtLevel{{$index}}.$invalid}" 
        id="beginsAtLevel{{$index}}">
    <p class="col-md-4 col-xs-4">Begin Level</p>
    <div class="col-md-8 col-xs-8">
        <input type="text"
            class="form-control" 
            name="beginsAtLevel{{$index}}" 
            ng-model="tier.beginsAtLevel" 
            ng-blur="rp.validateTiersBeginLevel(tiers);" 
            required>
        <div class="text-danger" 
            ng-messages="tierForm['beginsAtLevel'+ $index].$error" 
            ng-if="tierForm['beginsAtLevel'+ $index].$touched">
            <span ng-message="required">Begin Level is required</span>
        </div>
    </div>
</div>