Angular ng-repeat Error "Duplicates in a repeater are not allowed."

I was having an issue in my project where I was using ng-repeat track by $index but the products were not getting reflecting when data comes from database. My code is as below:

<div ng-repeat="product in productList.productList track by $index">
  <product info="product"></product>
 </div>

In the above code, product is a separate directive to display the product.But i came to know that $index causes issue when we pass data out from the scope. So the data losses and DOM can not be updated.

I found the solution by using product.id as a key in ng-repeat like below:

<div ng-repeat="product in productList.productList track by product.id">
  <product info="product"></product>
 </div>

But the above code again fails and throws the below error when more than one product comes with same id:

angular.js:11706 Error: [ngRepeat:dupes] Duplicates in a repeater are not allowed. Use 'track by' expression to specify unique keys. Repeater

So finally i solved the problem by making dynamic unique key of ng-repeat like below:

<div ng-repeat="product in productList.productList track by (product.id + $index)">
  <product info="product"></product>
 </div>

This solved my problem and hope this will help you in future.

The solution is actually described here: http://www.anujgakhar.com/2013/06/15/duplicates-in-a-repeater-are-not-allowed-in-angularjs/

AngularJS does not allow duplicates in a ng-repeat directive. This means if you are trying to do the following, you will get an error.

// This code throws the error "Duplicates in a repeater are not allowed.
// Repeater: row in [1,1,1] key: number:1"
<div ng-repeat="row in [1,1,1]">

However, changing the above code slightly to define an index to determine uniqueness as below will get it working again.

// This will work
<div ng-repeat="row in [1,1,1] track by $index">

Official docs are here: https://docs.angularjs.org/error/ngRepeat/dupes

For those who expect JSON and still getting the same error, make sure that you parse your data:

$scope.customers = JSON.parse(data)

What do you intend your "range" filter to do?

Here's a working sample of what I think you're trying to do: http://jsfiddle.net/evictor/hz4Ep/

HTML:

<div ng-app="manyminds" ng-controller="MainCtrl">
  <div class="idea item" ng-repeat="item in items" isoatom>    
    Item {{$index}}
    <div class="section comment clearfix" ng-repeat="comment in item.comments | range:1:2">
      Comment {{$index}}
      {{comment}}
    </div>
  </div>
</div>

JS:

angular.module('manyminds', [], function() {}).filter('range', function() {
    return function(input, min, max) {
        var range = [];
        min = parseInt(min); //Make string input int
        max = parseInt(max);
        for (var i=min; i<=max; i++)
            input[i] && range.push(input[i]);
        return range;
    };
});

function MainCtrl($scope)
{
    $scope.items = [
        {
            comments: [
                'comment 0 in item 0',
                'comment 1 in item 0'
            ]
        },
        {
            comments: [
                'comment 0 in item 1',
                'comment 1 in item 1',
                'comment 2 in item 1',
                'comment 3 in item 1'
            ]
        }
    ];
}