Question

Hey guys, im not well versed in dealing with asynchronous design patterns, and im having a problem writing a script that does two async data fetches.

Im using Dojo.data.api.Read.Fetch() to make two fetch() calls from seperate databases. The reulsts come back asynchronously. However, I have to cross reference the results, so i want my script to continue once BOTH async fetches are complete. I dont know how to do this, and therein lies the problem.

I am aware of the fetch’s onComplete field and how to use it, BUT the best case solution i see there is to call the second fetch in the onComplete of the first fetch. I would like to do these fetches at the same time. Is there a way to do this?

Here’s the current structure of my program for illustration purposes:


this.dict1.fetch({query:"blahblahblah", onComplete: function(items) { something here? }});
this.dict2.fetch({query:"blahblahbleh", onComplete: function(items) { or maybe something here? }});
this.orMaybeDoSomethingAfterBothFetches()

Any help would be greatly appreciated!

Answer 1

// this is a variation of a function I have answered quite a few similar questions on SO with
function collected(count, fn){
    var loaded = 0;
    var collectedItems = [];
    return function(items){
        collectedItems = collectedItems.concat(items);
        if (++loaded === count){
             fn(collectedItems);
        } 
    }
}

var collectedFn = collected(2, function(items){
    //do stuff
});


this.dict1.fetch({query:"blahblahblah", onComplete: collectedFn);
this.dict2.fetch({query:"blahblahbleh", onComplete: collectedFn);

An alternative solution is

var store = {
    exec: function(){
        if (this.items1 && this.items2) {
            // do stuff with this.items1 and this.items2
        }
    }
};

this.dict1.fetch({query:"blahblahblah", onComplete: function(items) {
    store.items1 = items;
    store.exec();
});
this.dict2.fetch({query:"blahblahbleh", onComplete: function(items) {
    store.items2 = items;
    store.exec();
});