JSONAPI::Resources Build Status

JSONAPI::Resources, or "JR", provides a framework for developing a server that complies with the JSON API specification.

Like JSON API itself, JR's design is focused on the resources served by an API. JR needs little more than a definition of your resources, including their attributes and relationships, to make your server compliant with JSON API.

JR is designed to work with Rails, and provides custom routes, controllers, and serializers. JR's resources may be backed by ActiveRecord models or by custom objects.

Demo App

We have a simple demo app, called Peeps, available to show how JR is used.

Installation

Add JR to your application's Gemfile:

gem 'jsonapi-resources'

And then execute:

$ bundle

Or install it yourself as:

$ gem install jsonapi-resources

Usage

Resources

Resources define the public interface to your API. A resource defines which attributes are exposed, as well as relationships to other resources.

Resource definitions should by convention be placed in a directory under app named resources, app/resources. The class name should be the single underscored name of the model that backs the resource with _resource.rb appended. For example, a Contact model's resource should have a class named ContactResource defined in a file named contact_resource.rb.

JSONAPI::Resource

Resources must be derived from JSONAPI::Resource, or a class that is itself derived from JSONAPI::Resource.

For example:

require 'jsonapi/resource'

class ContactResource < JSONAPI::Resource
end

Attributes

Any of a resource's attributes that are accessible must be explicitly declared. Single attributes can be declared using the attribute method, and multiple attributes can be declared with the attributes method on the resource class.

For example:

require 'jsonapi/resource'

class ContactResource < JSONAPI::Resource
  attribute :id
  attribute :name_first
  attributes :name_last, :email, :twitter
end

This resource has 5 attributes: :id, :name_first, :name_last, :email, :twitter. By default these attributes must exist on the model that is handled by the resource.

A resource object wraps a Ruby object, usually an ActiveModel record, which is available as the @model variable. This allows a resource's methods to access the underlying model.

For example, a computed attribute for full_name could be defined as such:

require 'jsonapi/resource'

class ContactResource < JSONAPI::Resource
  attributes :id, :name_first, :name_last, :email, :twitter
  attribute :full_name

  def full_name
    "#{@model.name_first}, #{@model.name_last}"
  end
end
Fetchable Attributes

By default all attributes are assumed to be fetchable. The list of fetchable attributes can be filtered by overriding the fetchable_fields method.

Here's an example that prevents guest users from seeing the email field:

class AuthorResource < JSONAPI::Resource
  attributes :id, :name, :email
  model_name 'Person'
  has_many :posts

  def fetchable_fields
    if (context.current_user.guest)
      super(context) - [:email]
    else
      super(context)
    end
  end
end

Context flows through from the controller and can be used to control the attributes based on the current user (or other value)).

Creatable and Updateable Attributes

By default all attributes are assumed to be updateable and creatable. To prevent some attributes from being accepted by the update or create methods, override the self.updateable_fields and self.createable_fields methods on a resource.

This example prevents full_name from being set:

require 'jsonapi/resource'

class ContactResource < JSONAPI::Resource
  attributes :id, :name_first, :name_last, :full_name

  def full_name
    "#{@model.name_first}, #{@model.name_last}"
  end

  def self.updateable_fields(context)
    super - [:full_name]
  end

  def self.createable_fields(keys, context)
    super - [:full_name]
  end
end

The context is not by default used by the ResourceController, but may be used if you override the controller methods. By using the context you have the option to determine the createable and updateable fields based on the user.

Sortable Attributes

JR supports sorting primary resources by multiple sort criteria.

By default all attributes are assumed to be sortable. To prevent some attributes from being sortable, override the self.sortable_fields method on a resource.

Here's an example that prevents sorting by post's body:

class PostResource < JSONAPI::Resource
  attribute :id, :title, :body

  def self.sortable_fields(context)
    super(context) - [:body]
  end
end
Attribute Formatting

Attributes can have a Format. By default all attributes use the default formatter. If an attribute has the format option set the system will attempt to find a formatter based on this name. In the following example the last_login_time will be returned formatted to a certain time zone:

class PersonResource < JSONAPI::Resource
  attributes :id, :name, :email
  attribute :last_login_time, format: :date_with_timezone
end

The system will lookup a value formatter named DateWithTimezoneValueFormatter and will use this when serializing and updating the attribute. See the Value Formatters section for more details.

Primary Key

Resources are always represented using a key of id. If the underlying model does not use id as the primary key you can use the primary_key method to tell the resource which field on the model to use as the primary key. Note: this doesn't have to be the actual primary key of the model. For example you may wish to use integers internally and a different scheme publicly.

class CurrencyResource < JSONAPI::Resource
  primary_key :code
  attributes :code, :name

  has_many :expense_entries
end

Model Name

The name of the underlying model is inferred from the Resource name. It can be overridden by use of the model_name method. For example:

class AuthorResource < JSONAPI::Resource
  attributes :id, :name
  model_name 'Person'
  has_many :posts
end

Associations

Related resources need to be specified in the resource. These are declared with the has_one and the has_many methods.

Here's a simple example where a post has a single author and an author can have many posts:

class PostResource < JSONAPI::Resource
  attribute :id, :title, :body

  has_one :author
end

And the corresponding author:

class AuthorResource < JSONAPI::Resource
  attribute :id, :name

  has_many :posts
end
Options

The association methods support the following options:

  • class_name - a string specifying the underlying class for the related resource
  • foreign_key - the method on the resource used to fetch the related resource. Defaults to <resource_name>_id for has_one and <resource_name>_ids for has_many relationships.
  • acts_as_set - allows the entire set of related records to be replaced in one operation. Defaults to false if not set.

Examples:

 class CommentResource < JSONAPI::Resource
  attributes :id, :body
  has_one :post
  has_one :author, class_name: 'Person'
  has_many :tags, acts_as_set: true
 end

class ExpenseEntryResource < JSONAPI::Resource
  attributes :id, :cost, :transaction_date

  has_one :currency, class_name: 'Currency', key: 'currency_code'
  has_one :employee
end

Filters

Filters for locating objects of the resource type are specified in the resource definition. Single filters can be declared using the filter method, and multiple filters can be declared with the filters method on the resource class.

For example:

require 'jsonapi/resource'

class ContactResource < JSONAPI::Resource
  attributes :id, :name_first, :name_last, :email, :twitter

  filter :id
  filters :name_first, :name_last
end
Finders

Basic finding by filters is supported by resources. This is implemented in the find, find_by_key and find_by_keys finder methods. Currently this is implemented for ActiveRecord based resources. The finder methods rely on the records method to get an Arel relation. It is therefore possible to override records to affect the three find related methods.

Customizing base records for finder methods

If you need to change the base records on which find, find_by_key and find_by_keys operate, you can override the records method on the resource class.

For example to allow a user to only retrieve his own posts you can do the following:

class PostResource < JSONAPI::Resource
  attribute :id, :title, :body

  def self.records(options = {})
    context = options[:context]
    context.current_user.posts
  end
end
Applying Filters

The apply_filter method is called to apply each filter to the Arel relation. You may override this method to gain control over how the filters are applied to the Arel relation.

For example to change how a

def apply_filter(records, filter, value)
  case filter
    when :visibility
      records.where('users.publicly_visible = ?', value == :public)
    when :last_name, :first_name, :name
      if value.is_a?(Array)
        value.each do |val|
          records = records.where(_model_class.arel_table[filter].matches(val))
        end
        return records
      else
        records.where(_model_class.arel_table[filter].matches(value))
      end
    else
      return super(records, filter, value)
  end
end
Override finder methods

Finally if you have more complex requirements for finding you can override the find, find_by_key and find_by_keys methods on the resource class.

Here's an example that defers the find operation to a current_user set on the context option:

class AuthorResource < JSONAPI::Resource
  attributes :id, :name
  model_name 'Person'
  has_many :posts

  filter :name

  def self.find(filters, options = {})
    context = options[:context]
    authors = context.current_user.find_authors(filters)

    return authors.map do |author|
      self.new(author)
    end
  end
end

Controllers

JSONAPI::Resources provides a class, ResourceController, that can be used as the base class for your controllers. ResourceController supports index, show, create, update, and destroy methods. Just deriving your controller from ResourceController will give you a fully functional controller.

For example:

class PeopleController < JSONAPI::ResourceController

end

Of course you are free to extend this as needed and override action handlers or other methods.

The context that's used for serialization and resource configuration is set by the controller's context method.

For example:

class ApplicationController < JSONAPI::ResourceController
  def context
    {current_user: current_user}
  end
end

# Specific resource controllers derive from ApplicationController
# and share its context
class PeopleController < ApplicationController

end

Error codes

Error codes are provided for each error object returned, based on the error. These errors are:

module JSONAPI
  VALIDATION_ERROR = 100
  INVALID_RESOURCE = 101
  FILTER_NOT_ALLOWED = 102
  INVALID_FIELD_VALUE = 103
  INVALID_FIELD = 104
  PARAM_NOT_ALLOWED = 105
  PARAM_MISSING = 106
  INVALID_FILTER_VALUE = 107
  COUNT_MISMATCH = 108
  KEY_ORDER_MISMATCH = 109
  KEY_NOT_INCLUDED_IN_URL = 110
  INVALID_INCLUDE = 112
  RELATION_EXISTS = 113
  INVALID_SORT_PARAM = 114

  RECORD_NOT_FOUND = 404
  LOCKED = 423
end

These codes can be customized in your app by creating an initializer to override any or all of the codes.

Serializer

The ResourceSerializer can be used to serialize a resource into JSON API compliant JSON. ResourceSerializer must be initialized with the primary resource type it will be serializing. ResourceSerializer has a serialize_to_hash method that takes a resource instance or array of resource instances to serialize. For example:

require 'jsonapi/resource_serializer'
post = Post.find(1)
JSONAPI::ResourceSerializer.new(PostResource).serialize_to_hash(PostResource.new(post))

This returns results like this:

{
  posts: {
    id: 1,
    title: 'New post',
    body: 'A body!!!',
    links: {
      section: nil,
      author: 1,
      tags: [1,2,3],
      comments: [1,2]
    }
  }
}

Serialize_to_hash method options

The serialize_to_hash method also takes some optional parameters:

include

An array of resources. Nested resources can be specified with dot notation.

Purpose: determines which objects will be side loaded with the source objects in a linked section

Example: include: ['comments','author','comments.tags','author.posts']

fields

A hash of resource types and arrays of fields for each resource type.

Purpose: determines which fields are serialized for a resource type. This encompasses both attributes and association ids in the links section for a resource. Fields are global for a resource type.

Example: fields: { people: [:id, :email, :comments], posts: [:id, :title, :author], comments: [:id, :body, :post]}

post = Post.find(1)
JSONAPI::ResourceSerializer.new(PostResource).serialize_to_hash(PostResource.new(post),
        include: ['comments','author','comments.tags','author.posts'],
        fields: {
                 people: [:id, :email, :comments],
                 posts: [:id, :title, :author],
                 tags: [:name],
                 comments: [:id, :body, :post]})
context

Context data can be provided to the serializer, which passes it to each resource as it is inspected.

Routing

JR has a couple of helper methods available to assist you with setting up routes.

jsonapi_resources

Like resources in ActionDispatch, jsonapi_resources provides resourceful routes mapping between HTTP verbs and URLs and controller actions. This will also setup mappings for relationship URLs for a resource's associations. For example

require 'jsonapi/routing_ext'

Peeps::Application.routes.draw do
  jsonapi_resources :contacts
  jsonapi_resources :phone_numbers
end

gives the following routes

                     Prefix Verb   URI Pattern                                               Controller#Action
contact_links_phone_numbers GET    /contacts/:contact_id/links/phone_numbers(.:format)       contacts#show_association {:association=>"phone_numbers"}
                            POST   /contacts/:contact_id/links/phone_numbers(.:format)       contacts#create_association {:association=>"phone_numbers"}
                            DELETE /contacts/:contact_id/links/phone_numbers/:keys(.:format) contacts#destroy_association {:association=>"phone_numbers"}
                   contacts GET    /contacts(.:format)                                       contacts#index
                            POST   /contacts(.:format)                                       contacts#create
                new_contact GET    /contacts/new(.:format)                                   contacts#new
               edit_contact GET    /contacts/:id/edit(.:format)                              contacts#edit
                    contact GET    /contacts/:id(.:format)                                   contacts#show
                            PATCH  /contacts/:id(.:format)                                   contacts#update
                            PUT    /contacts/:id(.:format)                                   contacts#update
                            DELETE /contacts/:id(.:format)                                   contacts#destroy
 phone_number_links_contact GET    /phone_numbers/:phone_number_id/links/contact(.:format)   phone_numbers#show_association {:association=>"contact"}
                            POST   /phone_numbers/:phone_number_id/links/contact(.:format)   phone_numbers#create_association {:association=>"contact"}
                            DELETE /phone_numbers/:phone_number_id/links/contact(.:format)   phone_numbers#destroy_association {:association=>"contact"}
              phone_numbers GET    /phone_numbers(.:format)                                  phone_numbers#index
                            POST   /phone_numbers(.:format)                                  phone_numbers#create
           new_phone_number GET    /phone_numbers/new(.:format)                              phone_numbers#new
          edit_phone_number GET    /phone_numbers/:id/edit(.:format)                         phone_numbers#edit
               phone_number GET    /phone_numbers/:id(.:format)                              phone_numbers#show
                            PATCH  /phone_numbers/:id(.:format)                              phone_numbers#update
                            PUT    /phone_numbers/:id(.:format)                              phone_numbers#update
                            DELETE /phone_numbers/:id(.:format)                              phone_numbers#destroy
jsonapi_resource

Like jsonapi_resources, but for resources you lookup without an id.

You can control the relationship routes by passing a block into jsonapi_resources or jsonapi_resource. An empty block will not create any relationship routes.

You can add relationship routes in with jsonapi_links, for example:

Rails.application.routes.draw do
  jsonapi_resources :posts, except: [:destroy] do
    jsonapi_link :author, except: [:destroy]
    jsonapi_links :tags, only: [:show, :create]
  end
end

This will create relationship routes for author (show and create, but not destroy) and for tags (again show and create, but not destroy).

Formatting

JR by default uses some simple rules to format an attribute for serialization. Strings and Integers are output to JSON as is, and all other values have .to_s applied to them. This outputs something in all cases, but it is certainly not correct for every situation.

If you want to change the way an attribute is serialized you have a couple of ways. The simplest method is to create a getter method on the resource which overrides the attribute and apply the formatting there. For example:

class PersonResource < JSONAPI::Resource
  attributes :id, :name, :email
  attribute :last_login_time

  def 
    @model..in_time_zone(@context[:current_user].time_zone).to_s
  end
end

This is simple to implement for a one off situation, but not for example if you want to apply the same formatting rules to all DateTime fields in your system. Another issue is the attribute on the resource will always return a formatted response, whether you want it or not.

Value Formatters

To overcome the above limitations JR uses Value Formatters. Value Formatters allow you to control the way values are handled for an attribute. The format can be set per attribute as it is declared in the resource. For example:

class PersonResource < JSONAPI::Resource
  attributes :id, :name, :email
  attribute :last_login_time, format: :date_with_timezone
end

A Value formatter has a format and an unformat method. Here's the base ValueFormatter and DefaultValueFormatter for reference:

module JSONAPI
  class ValueFormatter < Formatter
    class << self
      def format(raw_value, context)
        super(raw_value)
      end

      def unformat(value, context)
        super(value)
      end
      ...
    end
  end
end

class DefaultValueFormatter < JSONAPI::ValueFormatter
  class << self
    def format(raw_value, context)
      case raw_value
        when String, Integer
          return raw_value
        else
          return raw_value.to_s
      end
    end
  end
end

You can also create your own Value Formatter. Value Formatters must be named with the format name followed by ValueFormatter, i.e. DateWithTimezoneValueFormatter and derive from JSONAPI::ValueFormatter. It is recommended that you create a directory for your formatters, called formatters.

The format method is called by the ResourceSerializer as is serializing a resource. The format method takes the raw_value, and context parameters. raw_value is the value as read from the model, and context is the context of the current user/request. From this you can base the formatted version of the attribute current context.

The unformat method is called when processing the request. Each incoming attribute (except links) are run through the unformat method. The unformat method takes the value, and context parameters. value is the value as it comes in on the request, and context is the context of the current user/request. This allows you process the incoming value to alter its state before it is stored in the model. By default no processing is applied.

Use a Different Default Value Formatter

Another way to handle formatting is to set a different default value formatter. This will affect all attributes that do notw have a format set. You can do this by overriding the default_attribute_options method for a resource (or a base resource for a system wide change).

  def default_attribute_options
    {format: :my_default}
  end

and

class MyDefaultValueFormatter < JSONAPI::ValueFormatter
  class << self
    def format(raw_value, context)
      case raw_value
        when String, Integer
          return raw_value
        when DateTime
          return raw_value.in_time_zone(context[:current_user].time_zone).to_s
        else
          return raw_value.to_s
      end
    end
  end
end

This way all DateTime values will be formatted to display in the specified timezone.

Key Format

JSONAPI is agnostic on the format of the keys used in the responses. By default JR uses underscored keys which match the attribute names used by rails models. This can be changed by specifying a different key formatter.

For example to use camel cased keys with an initial lowercase character (JSON's default) create an initializer and add the following:

JSONAPI.configure do |config|
  # built in key format options are :underscored_key, :camelized_key and :dasherized_key
  config.json_key_format = :camelized_key
end

This will cause the serializer to use the CamelizedKeyFormatter. Besides UnderscoredKeyFormatter and CamelizedKeyFormatter JR defines the DasherizedKeyFormatter. You can also create your own KeyFormatter, for example:

class UpperCamelizedKeyFormatter < JSONAPI::KeyFormatter
  class << self
    def format(key)
      super.camelize(:upper)
    end
  end
end

You would specify this in JSONAPI.configure as :upper_camelized.

Contributing

  1. Fork it ( http://github.com/cerebris/jsonapi-resources/fork )
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create a new Pull Request

License

Copyright 2014 Cerebris Corporation. MIT License (see LICENSE for details).