Jbuilder::Jpartial

A lightweight library that provides a simple DSL for faster partial rendering with Jbuilder.

Add this line to your application's Gemfile:

gem 'jbuilder-jpartial', require: 'jbuilder/jpartial'

And then execute:

$ bundle

Or install it yourself as:

$ gem install jbuilder-jpartial

require 'jbuilder/jpartial'

jpartial._post do |post|
  json.title post.title
  json.author post.author.name
  json.content post.content
  json.partial! 'comments/comment'
  json.set! 'comments', post.comments do |comment|
    json._comment comment
  end
end

jpartial._comment do |comment|
  json.content comment.content
  json.author comment.author.name
end

json.partial! 'post'
json.set! 'posts', @posts do |post|
  json._post post
end

{
    "posts": [
        {
            "title": "The Best of Posts",
            "author": "M. Simon Borg",
            "content": "Pizza time!",
            "comments": [
                { "content": "So good", "author": "Matt's mom" },
                { "content": "I agree", "author": "Matt's dad" }
            ]
        }
    ]   
}

When partials are used with Jbuilder render times and memory usage can skyrocket quickly with the number of records, i.e. the number of partials rendered.

Using a simple DSL, Jbuilder::Jpartial lets you define your partials in a familiar way while dramatically reducing overhead.

The result is faster rendering and lower memory usage, while still being able to leverage the advantages of Jbuilder. In the above example, if we had used standard Jbuilder partials those templates would have to be rendered once for each post and/or comment. If you have 50 posts, each with 50 comments, that's 2,550 templates rendered! Using Jbuilder::Jpartial, the partial files are each only called when the partial is initialized. After that, all of the partial rendering is taken care of in the abstract from the original file. In our example, we hit json.partial! 'post' once and json.partial! 'comments/comment' only once for each post, cutting 2,550 template renders down to 51.

Alternatively you can define all partials in one initializer file and call them wherever you need them: from within other partial definitions or anywhere you use Jbuilder in your views. The big advantage here is since they're initialized at start up, you don't need to call any additional view templates to render the partials. Using the same example as above:

$ rails generate jpartial

Jbuilder::Jpartial.configure do |jpartial|
  jpartial._post do |post|
    json.title post.title
    json.author post.author.name
    json.content post.content
    json.set! 'comments', post.comments do |comment|
      json._comment comment
    end
  end

  jpartial._comment do |comment|
    json.content comment.content
    json.author comment.author.name
  end
end

json.set! 'posts', @posts do |post|
  json._post post
end

Notice that when using this method, we don't make any calls like json.partial! 'post' at any point to define the partial before using it. All of the partials are already defined in the initializer file.

We've now cut our template renders down to only 1 from the original 2,550. The only real disadvantage is it bucks the regular Rails file structure conventions for partials. C'est la vie.

Each method you call on jpartial defines a Jbuilder method of the same name. The objects you will pass to that method are yielded to the block. Inside the block you can use plain old Jbuilder syntax, and access any of the helper methods available in your views.

e.g.

jpartial._post do |post|
  json.post_url post_url(post)
end

Now in your .jbuilder templates you can call json._post @post.

You can specify multiple arguments and even use keyword options if you need to pass more than one local variable to the partial. You can also call partial methods from within other partial methods.

The rule of thumb when defining your partials in view templates is you need to make sure the partial is initialized by making a call to the template, outside of your render logic and/or any loops/iteration.

e.g.

jpartial._author do |author|
  json.name author.name
end

jpartial._post do |post, author:|
  json.title post.title
  json.partial! 'authors/author'
  json._author author
end

Now you can call json._post @post, author: @author

Again, if you're defining all of your partials in one config file (best performance), the extra call to a partial template is not necessary.

Jbuilder::Jpartial.configure do |jpartial|
  jpartial._post do |post, author:|
    json.title post.title
    json._author author
  end

  jpartial._author do |author|
    json.name author.name
  end
end

However unlikely, if you try to name a partial with the same name as a method already defined by Jbuilder it will throw an error at start up. Just pick a different name, like #whatever_partial instead of #whatever.

After checking out the repo, run bin/setup to install dependencies. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/msimonborg/jbuilder-jpartial.

The gem is available as open source under the terms of the MIT License.