Angular Promises Sequential loop

Question

I have the following set of data.

 $scope.orders = [
        { material: 'A', quantity: 32, orderNumber: 'dummy'},
        { material: 'A', quantity: 65, orderNumber: 'dummy'},
        { material: 'A', quantity: 86, orderNumber: 'dummy'},

        { material: 'B', quantity: 45, orderNumber: 'dummy'},
        { material: 'B', quantity: 68, orderNumber: 'dummy'},
        { material: 'B', quantity: 15, orderNumber: 'dummy'},

        { material: 'C', quantity: 11, orderNumber: 'dummy'}
    ];

I want to process (createOrder) the orders grouped by material. After all the orders for that particular material have been processed I want to call another function (materialRun) that does a material run. After this function is successful the next material (with its corresponding orders) has to be processed etc.. All these calls have to be sequential because the backend cannot process everything in parallel.

So i'm searching for something like this:

material A: order 1 -> order 2 -> order 3 -> materialRun

when the materialRun from A is done, start material B

material B: order 1 -> order 2 -> order 3 -> materialRun

when the materialRun from B is done, start material C

...

I also need the result from each createOrder to update the orders list

I'm using angular promises for now but i'm open for suggestions. I hope this fiddle helps: http://jsfiddle.net/a1sp0ye2/

"All these calls have to be sequential because the backend cannot process everything in parallel." - uh, you know, maybe you should fix the backend? It would be reasonable at least if you could put all updates in a single request, and let the backend figure out how to process that. — Bergi
– Bergi, Commented Apr 22, 2015 at 12:38
@Grundy the table updated with the correct order numbers, I will also add some more feedback when an order has been succesfully processed. Like a background color on the table row or something like that — Stvenoo
– Stvenoo, Commented Apr 22, 2015 at 12:41
@Stvenoo correct order numbers how you detect correct numbers? — Grundy
– Grundy, Commented Apr 22, 2015 at 12:44

Nikos Paraskevopoulos · Accepted Answer · 2015-04-22 13:06:06Z

The following is a template for loops with asynchronous bodies, i.e. the next iteration must take place only when an asynchronous task is complete. It works for promises in an Angular context, but can be generalized for any promises implementation I believe:

/**
 * Loop the items array asynchronously.
 *
 * @param items - Array to iterate
 * @param doLoopBody - Callback that executes the body loop, returns promise
 */
function asyncLoop(items, doLoopBody) {
    var i = 0, d = $q.defer();

    nextIteration();

    return d.promise;

    function nextIteration() {
        if( i < items.length ) {
            doLoopBody(items[i], i, items).then(
                function() {
                    i++;
                    nextIteration();
                },
                onError
            );
        }
        else {
            d.resolve();
        }
    }

    function onError(reason) {
        d.reject(reason);
    }
}

Based on this, here is a crude implementation of your case (watch the browser's console for output).

Oleksii · Accepted Answer · 2015-04-24 08:38:10Z

0

I'm not sure that is can help you, but try to use my code:jsfiddle

        $scope.promises = [];
        ordersByMaterial.forEach(function(order) {
            $scope.promises.push(createOrder(order));
        });

I tried to test it by creating $scope.logsCreateValue = []; where I keep random values from Math.floor(Math.random() * 10); See to the console.log($scope.logsCreateValue);, it should matches with values from $scope.orders[key].orderNumber = res[key].orderNumber;

answered Apr 24, 2015 at 8:38

Oleksii

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