Format-agnostic templating for API responses
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Phat: Preprocessed Hashes & Arrays as Templating

Phat helps you generate JSON and XML repsonses using the same template files. A Phat template is plain Ruby code: whatever it returns, will get converted to JSON or XML.

The system consists of a template handler and the handy to_phat method defined on hashes, arrays and - currently - ActiveRecord model objects.


Currently Phat is available as a plugin, though we will soon be packaging it also as a gem. Clone this repository under your Rails 3 application's vendor/plugins/ folder and you can start using Phat right away.

Phat templates have the extension .phat. If you name them action.phat, they will catch all formats that have no explicitly designated templates, but of course you can just call them e.g. action.json.phat to restrict the format.

An example

An example Phat template might look like this:

{ users: @users.to_phat(
    only: 'name',
    merge: { path: ->(user) { user_path(user) }},
    refs: {
      pets: {
        only: %w(name species),
        merge: { path: ->(pet) { pet_path(pet) }}}})}

It will yield the following output (pretty printed here for readability):

{ "users": [
  { "name": "Jamie",
    "path": "/users/jamie",
    "pets": [
      { "name": "Wordsworth",
        "species": "Canis lupus familiaris",
        "path": "/pets/wordsworth" }]},
  { "name": "Jon Arbuckle",
    "path": "/users/jon",
    "pets": [
      { "name": "Garfield",
        "species": "Felis silvestris catus",
        "path": "/pets/garfield" },
      { "name": "Odie",
        "species": "Canis lupus familiaris",
        "path": "/pets/odie" }]}]}

The variable @users is an array (or an Arel relation), so as you can see, parameters meant to be used by ActiveRecord::Base#to_phat will cascade down through enumerables.

You can control the inclusion of AR fields and custom methods using only, also and except. If you do not wish to include any AR attributes in the output, use only: nil. If you want to include all AR attributes and throw in some custom method calls, use the also keyword.

The merge keyword makes it possible to add calculated fields into the output, this is most useful with generated URL's.

Phat is able to look into all kinds of AR reflections with the refs keyword; they will be represented either as arrays or a single object. All the above keywords (and refs itself) can be applied and will cascade.

In definitions under refs you can use the transform keyword to add a Proc that will be used to transform said reference:

{ users: @users.to_phat(
    only: 'name',
    refs: {
      pets: {
        transform: ->(pets) { pets.where(:active, true) },
        only: %w(name species) }})}