Problem of iteration on subcollection that modifies model triggering attributes

[alexstrat]

I've got a sub-collection that filters on an attribute value.

When I iterate on this sub-collection to modify attribute's value (the modification should remove the model from the collection), only half of the models are concerned by the modification.

coll = new Backbone.Collection();

for(var i=0; i<10; i++){
    coll.add(new Backbone.Model({
      id : 'model_'+i,
      selected: true
    }));
}

sub = coll.subcollection({
    filter: function(model) {
        return model.get('selected');
    },
    triggers: 'selected'
});


console.log('sub.length '+sub.length);
// sub.length 10

sub.each(function(model) {
    console.log('unselect '+model.get('id'));
    model.set('selected', false);
});
// unselect model_0
// unselect model_2 
// unselect model_4
// unselect model_6
// unselect model_8

console.log('sub.length '+sub.length);
// sub.length 5

I reproduced the bug in http://jsbin.com/elisor/3/edit.
I'm not sure it's a bug, since iterating on a collection that modifies itself is maybe not a feature, but I would like to know the workaround in this case.

However, Backbone handles well the case of removing of model while iterating on a collection. EDIT: backbone does not support that (http://jsbin.com/elisor/2/edit)

[alexstrat]

For the moment I found this workaround: http://jsbin.com/elisor/4/edit

sub.clone().each(function(model) {
    console.log('unselect '+model.get('id'));
    model.set('selected', false);
});

[anthonyshort]

It's the each method that is the problem. Iterating over the collection and removing things mid-way will cause issues. In the past I've manually looped over the models in the collection or cloned it like you had there.

You could also silence those changes and call the refresh method on the subset so it will update.

sub.each(function(model) {
    console.log('unselect '+model.get('id'));
    model.set('selected', false, { silent: true });
}).filterer.refresh();

Not the prettiest but you'll always have issues with things like this with the each method. I'll have a think about it. Maybe there is a better solution.