def random_model(ctx, model_class_name):
    """
    Get a random model identifier by class name. For example::

        # db/fixtures/Category.yml
        {% for i in range(0, 10) %}
        category{{ i }}:
            name: {{ faker.name() }}
        {% endfor %}

        # db/fixtures/Post.yml
        a_blog_post:
            category: {{ random_model('Category') }}

    Will render to something like the following::

        # db/fixtures/Post.yml (rendered)
        a blog_post:
            category: "Category(category7)"

    :param ctx: The context variables of the current template (passed automatically)
    :param model_class_name: The class name of the model to get.
    """
    model_identifiers = ctx['model_identifiers'][model_class_name]
    if not model_identifiers:
        return 'None'
    idx = random.randrange(0, len(model_identifiers))
    return '"%s(%s)"' % (model_class_name, model_identifiers[idx])