Feature Request: Fragment Renderer

[jochen777]

I think we need a "fragment renderer" mechanism in pebble. It acts like an include/macro but has an additional Java-Class attached, that can execute business logic or queries the database.

Example:

In template: {% render "latestPosts" with {"count":5} %}

In Java:

public class LatestPosts implements PebbleFramgmentRenderer {
  public Map render (Object... args) {
     ...
     model.put("posts", getLatestsPosts());
  }

  public String provideTemplateName() {
    return "/framgements/latestPosts"; 
}

In Template: (/framgements/latestPosts)

{% for post in posts %}
    <h3>{{ post.title }}</h3>
{% endfor %}

In configuration:

public class PebbleExtension extends AbstractExtension {
@Override
public Map<String, FragmentRenderer> getFragmentRenderer () {
 Map<String, FragmentRenderer> renderer = new HashMap();
 renderer.put("latestPosts", new LatestsPosts());
 return renderer;
}
}

.net has View Components (https://docs.asp.net/en/latest/mvc/views/view-components.html), symfony has Subrequests (http://symfony.com/doc/current/templating/embedding_controllers.html). I think, the .net approach is very good for this.

if the current HttpServletRequest could be passed to the "render" method, this would be even more useful!

[electrotype]

I do something similar to this using a plain function. In the function, I use a PebbleEngine to render a "fragment" and use the result to generate the result of the function itself.

The only difference I see from your example is that the current PebbleEngine could be more easily available from inside a function/filter. I inject mine using Guice since my custom Extension is part of the Guice context.

[jochen777]

That is a nice idea. I'll try this - thank you!

[decebals]

@jochen777 Have you come to a conclusion? Can you share some code?

[mbosecke]

At first I really liked this idea but the more I think about it the more it feels like we would just be implementing a new technique for something that is already possible. I think I'm of the opinion that this feature is better implemented at the application/framework level instead of within the Pebble library (similar to how this feature exists in Symfony but does not exist in the Twig library). A framework may already have something that is synonymous with a "fragment renderer" (ex. a controller in an MVC app) and implement it with that in mind, similar to how Symfony did theirs. I may put more thought into implementing this feature into our pebble-spring4 library.

Below I've listed a couple alternate methods of how we can access native Java code prior to rendering a sub-template; the first being suggested by @electrotype. Neither of which require a lot of code and both could easily be expanded or made more generic.

Custom Pebble function that internally invokes a PebbleEngine

main.html:

{{ latestPosts() }}

custom pebble function:

public String latestPosts(Map<String, Object> args) {
  Map<String, Object> context = new HashMap<>();
  context.put("posts", database.query("SELECT * FROM posts")); 
  PebbleEngine engine = new PebbleEngine.Builder().build();
  return engine.getTemplate('/fragments/latestPosts').evaluate(new StringWriter(), context);
}

Logic contained within the provided context

main.html:

{% include '/fragments/latestPosts' %}

/fragments/latestPosts.html:

{% for post in latestPosts.posts %} {{ post }} {% endfor %}

LatestPostsRenderer.java:

public class LatestPostsRenderer {
  public List<Post> posts(){
    return database.query("SELECT * FROM posts");
  }
} 

rendering the main template:

Map<String, Object> context = new HashMap<>();
context.put("latestPosts", new LatestPostsRenderer()); 
PebbleEngine engine = new PebbleEngine.Builder().build();
return engine.getTemplate("main").evaluate(new StringWriter(), context);

[jochen777]

Thank you for your answer!

The problem with the custom-function: It does not get a handle to the current http-request. So you can't react on cookies or the current path...

And the problem with provided context: Your controller must be aware of that and collect all data.

I agree with you, that this may be better included in the webframework-integration layer. So I really would love to have it in the pebble-spring4 project!

But in the first place, the custom function can solve a lot of problems like this for me. I can easily access the Pebble-engine within the spring - context.

[electrotype]

The problem with the custom-function: It does not get a handle to the current http-request. So you can't react on cookies or the current path...

Maybe you could use RequestContextHolder?

ServletRequestAttributes attr = (ServletRequestAttributes) RequestContextHolder.currentRequestAttributes();

[jochen777]

Yes, I know RequestContextHolder. But it is kind of ugly and hard to test... (But of course better than nothing!)