Ember many to many relationship - add a new object if one does not already exist

I have two models with a many to many relationship to each other - the first is 'recipe', the second is 'tag':

App.Recipe = DS.Model.extend({
    title: attr('string'),
    source: attr('string'),
    notes: attr('string'),
    isFavourite: attr('boolean', {defaultValue: false}),
    tags: hasMany('tag', { async: true })
});

App.Tag = DS.Model.extend({
    name: attr('string'),
    recipes: hasMany('recipe', { async: true })
});

In my template, I have an input for adding a tag to a recipe. User can add either one tag, or multiple by separating each tag with a comma.

{{input type="text" enter="AddTags" placeholder="add a tag (or two!)"}}

This calls 'AddTags' within my RecipeController:

App.RecipeController = Ember.ObjectController.extend({
    actions: {
        AddTags: function(tags){
            var store = this.store;
            var thisRecipe = this.get('model');
            var thisRecipeTags = thisRecipe.get('tags');
            var addedTags = tags.split(',');

            for (i = 0; i < addedTags.length; i++) {
                tag = store.createRecord('tag', {
                    name: addedTags[i]
                });

                thisRecipeTags.addObject(tag);
            }
        }
    }
});

This works wonderfully - however - I would like to refactor the function so that a new tag is only created if one with the same name doesn't already exist:

AddTags: function(tags){
    var store = this.store;
    var thisRecipe = this.get('model');
    var thisRecipeTags = thisRecipe.get('tags');
    var addedTags = tags.split(',');
    for (i = 0; i < addedTags.length; i++) {
        // If exisiting tag where name == addedTags[i]
            tag = existing tag object here
        // Else create a new tag
            tag = store.createRecord('tag', {
                name: addedTags[i]
            });

        thisRecipeTags.addObject(tag);
    }
}

How can I do this?

Update: I have set up a JS bin with the relevant code here: http://ift.tt/17IogiL