filtering collection from backbone with attributes - collections

Question

I've got a backbone collection and I'm trying to filter by an id within the attributes
basically, a user has classes, and the class has a location_id, and I want to filter by the location id. My collection looks like this to give you an idea.
-user
-models
-0
-attributes
-location_id
-1
-attributes
-location_id
-2
-attributes
-location_id
I thought I could filter this by using
var get_locations = user_class_collection.filter(function(classes){
console.log(classes);
return classes.get(location_id)==location.id;
});
console.log(get_locations);
but that is returning an empty array, when I know the location_id is in the collection.
Any idea why this isn't working? I've also tried to grab classes.attributes.get, but it wasn't any better
In the first few responses, it was properly mentioned that I had to quote the get('location_id'). I've now done that, but unfortunately, I'm still getting an empty array. I thought that the filter would loop through the classes and I would get a console output for each class, but the console.log(classes) is only getting triggered once. Is that a hint? Or a red-herring?

Answer 1

you are trying to get a property from classes that is named as the value of the location_id parameter
you should instead make that a string (in fact you can choose how you make it a string, single or double quotes both work)
user_class_collection.filter(function(classes){
return classes.get('location_id') == location.id;
});

Answer 2

For filtering collection using backbone the best approach is to use a filtered function in your collection
var UserCollection = Backbone.Collection.extend ({
filtered : function ( id ) {
I suggest to use UnderScore filter which will return true for valid and false for invalid where true is what you are looking for. use this.models to get the current collection models use model.get( '' ) to get the element you want to check for
var results = _.filter( this.models, function ( model ) {
if ( model.get('location_id') == id )
return true ;
return false ;
});
Then use underscore map your results and transform it to JSON like
results = _.map( results, function( model ) { return model.toJSON() } );
Finally returning a new backbone collection with only results
return new Backbone.Collection( results ) ;
Optionally if you don't want to keep all the data in the collection but just the filtered one you should reset the collection and skip the above return like
this.reset( results ) ;
View call the filtered collection and the render the result

Answer 3

Try this:
user_class_collection.select(function(classes){
return classes.get("location_id")==location.id;
});