如何在Symfony2中创建动态模板选择器？

Question

I would like to create a dynamic template locator. Basically, I would like to prioritize templates from certain bundle when some global conditions are met. Similar to how bundle inheritance works, but runtime-dynamic.

It should work like this: I've got kind of 'categories' and each category has its own bundle. When a template is to be rendered I would check which category is currently set and search for this template in this category's bundle. If not found then fallback to built-in mechanism.

I though about overriding Symfony\\Bundle\\FrameworkBundle\\Templating\\Loader\\TemplateLocator , but this seems a bit hackish. I would like to mimick the bundle inheritance if possible, but I cannot find where it is implemented.

How would you approach this? Is TemplateLocator the best place to inject my logic?

Answer 1

This may not be the prettiest solution but it works like a charm.

I subclassed and overloaded the TemplateLocator service:

class CategoryAwareTemplateLocator extends TemplateLocator
{
    /**
     * @var string
     */
    protected $categoryBundle = null;

    /**
     * @var string
     */
    protected $defaultBundle = null;

    /**
     * {@inheritDoc}
     */
    public function __construct(FileLocatorInterface $locator, $cacheDir = null)
    {
        parent::__construct($locator, $cacheDir);
    }

    /**
     * {@inheritDoc}
     */
    public function locate($template, $currentPath = null, $first = true)
    {
        if(!$template instanceof TemplateReferenceInterface) {
            throw new \InvalidArgumentException('The template must be an instance of TemplateReferenceInterface.');
        }

        $templateParameters = $template->all();
        $templateBundle = array_key_exists('bundle', $templateParameters) ? $templateParameters['bundle'] : null;

        if(
            null !== $this->categoryBundle &&
            $templateBundle === $this->defaultBundle /* Override only defaultBundle templates */
        ) {
            /* Try our category bundle first */
            $categoryTemplate = clone $template;
            $categoryTemplate->set('bundle', $this->categoryBundle);

            try {
                return parent::locate($categoryTemplate, $currentPath, $first);
            } catch(\InvalidArgumentException $exception) {
                /* Just fall through to default mechanism */
            }
        }

        return parent::locate($template, $currentPath, $first);
    }

    /**
     * @param string $defaultBundle
     * @param string $categoryBundle
     */
    public function setCategoryBundle($defaultBundle, $categoryBundle)
    {
        $this->categoryBundle = $categoryBundle;
        $this->defaultBundle = $defaultBundle;
    }
}

The desired bundle name is injected at runtime via setter (it's not known at 'compile-time'). This is a bit ugly too.

The great thing is that this works for all twig tags ( include , use , ...). The only problem is that you cannot access the 'default' template you are overriding. If you try to do it from the template that overrides it you will get nesting level (infinite recursion) error.

This is not a biggie since you can cleverly 'inherit' from the base templates using composition (splitting the templates into smaller ones).