Update backbone.js model with new array element

Question

I have a backbone.js model similar to the one shown below.

Filters = Backbone.Model.extend({
    defaults : {
        title: [ ["title1", "easy"], ["title2", "hard"] ]
    }
});

I'm trying to add an element to the first-level array, such that the model then becomes:

Filters = Backbone.Model.extend({
    defaults : {
        title: [ ["title1", "easy"], ["title2", "hard"], ["title3", "medium"] ]
    }
});

The code I have right now is this:

function setFilters() { 
    var options = {};   

    for (var facet in facets) {
        for (var facetKey in facets[facet]) {
            if (!filterExists(facetKey)) {
                options[facetKey] = new Array(new Array(facets[facet][facetKey], "equals"));
            }
            else {
                (filters[facetKey]).push(new Array(facets[facet][facetKey], "equals"));
            }
        }
    }

    filters.set(options);
}

The function filterExists simply checks if the key "title" is present in the model. When I run this, it says that filters[facetKey] is undefined. But isn't this the first-level array I need to push my element into?

Offtopic: instead of new Array(new Array(facets[facet][facetKey], "equals")) why not you write the much shorter [[ facets[facet][facetKey], "equals"]]? Is filters a global variable? filters or Filters? — biziclop
– biziclop, Commented Feb 20, 2012 at 17:22
@biziclop yes, filters is a global variable. Thanks for the tip on the arrays. — kaspnord
– kaspnord, Commented Feb 20, 2012 at 17:24
Also { {"title1", "easy"}, {"title2", "hard"} } should be [ ["title1", "easy"], ["title2", "hard"] ]. {} is for creating objects: { name:'Joe', city:'London' } — biziclop
– biziclop, Commented Feb 20, 2012 at 17:32
@biziclop, yes I'll change that now to prevent confusion in the future. — kaspnord
– kaspnord, Commented Feb 20, 2012 at 18:56

biziclop · Accepted Answer · 2012-12-27 23:23:40Z

7

You can access model attributes with .get() and .set() functions, or directly via the .attributes property:

http://documentcloud.github.com/backbone/#Model-attributes

var filters = new Filters();
filters.attributes.facetKey.push( [...] );

OR

filters.set('facetKey', ( filters.get('facetKey') || []).concat([...]));

Anyway, here is your transformed function which may or may not work:

function setFilters() { 
    for (var facet in facets) {
        for (var facetKey in facets[facet]) {
            var f = [ facets[facet][facetKey], "equals" ];

            if( filterExists(facetKey)) {
            // OR: if( filters.attributes[ facetKey ]){
                filters.attributes[ facetKey ].push( f );
            }else{
                filters.attributes[ facetKey ] = [ f ];
            }
        }
    }

    // trigger change event for all attributes
    filters.set( filters.attributes );
}

Bonus:

(filters.attributes[ facetKey ] = filters.attributes[ facetKey ] || [] ).push(f);

edited Dec 27, 2012 at 23:23

answered Feb 20, 2012 at 17:30

biziclop

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8 Comments

driangle Over a year ago

but will this trigger a change event?

biziclop Over a year ago

Only using .set() would trigger any events, directly accessing an object's property can't trigger anything (unless setters are somehow involved).

driangle Over a year ago

I think this is a good answer, since it accomplishes what the @kaspnord was asking, but since 'event' triggering does not automatically occur it could cause problems. For example if there are views waiting for changes to re-render themselves, etc. Maybe you should manually trigger the event after adding the element?

kaspnord Over a year ago

Thanks guys, this works! Looks like I was treating the models object as an array, which was why I couldn't access it. Also, thanks for the alternative to 'filterExists'... it's much better :)

poorman Over a year ago

filters.set('facetKey', filters.get('facetKey').push(...)); // BackBone 0.9 FTW will not work because array.push() returns the length of the array not the array itself. you have to separate that out

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