Fast JSON API

A lightning fast JSON:API serializer for Ruby Objects.

Performance Comparison

We compare serialization times with Active Model Serializer as part of RSpec performance tests included on this library. We want to ensure that with every change on this library, serialization time is at least 25 times faster than Active Model Serializers on up to current benchmark of 1000 records. Please read the performance document for any questions related to methodology.

Benchmark times for 250 records

$ rspec
Active Model Serializer serialized 250 records in 138.71 ms
Fast JSON API serialized 250 records in 3.01 ms

Table of Contents

• Features
• Installation
• Usage
  • Rails Generator
  • Model Definition
  • Serializer Definition
  • Object Serialization
  • Compound Document
  • Key Transforms
  • Collection Serialization
  • Caching
  • Params
  • Conditional Attributes
  • Conditional Relationships
  • Sparse Fieldsets
  • Using helper methods
• Contributing

Features

• Declaration syntax similar to Active Model Serializer
• Support for belongs_to, has_many and has_one
• Support for compound documents (included)
• Optimized serialization of compound documents
• Caching

Installation

Add this line to your application's Gemfile:

gem'fast_jsonapi'

Execute:

$ bundle install

Usage

Rails Generator

You can use the bundled generator if you are using the library inside of a Rails project:

rails g serializer Movie name year

This will create a new serializer in app/serializers/movie_serializer.rb

Model Definition

classMovieattr_accessor:id,:name,:year,:actor_ids,:owner_id,:movie_type_idend

Serializer Definition

classMovieSerializerincludeFastJsonapi::ObjectSerializerset_type:movie# optionalset_id:owner_id# optionalattributes:name,:yearhas_many:actorsbelongs_to:owner,record_type: :userbelongs_to:movie_typeend

Sample Object

movie=Movie.newmovie.id=232movie.name='test movie'movie.actor_ids=[1,2,3]movie.owner_id=3movie.movie_type_id=1movie

Object Serialization

Return a hash

hash=MovieSerializer.new(movie).serializable_hash

Return Serialized JSON

json_string=MovieSerializer.new(movie).serialized_json

Serialized Output

{
"data": {
"id": "3",
"type": "movie",
"attributes": {
"name": "test movie",
"year": null
},
"relationships": {
"actors": {
"data": [
{
"id": "1",
"type": "actor"
},
{
"id": "2",
"type": "actor"
}
]
},
"owner": {
"data": {
"id": "3",
"type": "user"
}
}
}
}
}

Key Transforms

By default fast_jsonapi underscores the key names. It supports the same key transforms that are supported by AMS. Here is the syntax of specifying a key transform

classMovieSerializerincludeFastJsonapi::ObjectSerializer# Available options :camel, :camel_lower, :dash, :underscore(default)set_key_transform:camelend

Here are examples of how these options transform the keys

set_key_transform:camel# "some_key" => "SomeKey"set_key_transform:camel_lower# "some_key" => "someKey"set_key_transform:dash# "some_key" => "some-key"set_key_transform:underscore# "some_key" => "some_key"

Attributes

Attributes are defined in FastJsonapi using the attributes method. This method is also aliased as attribute, which is useful when defining a single attribute.

By default, attributes are read directly from the model property of the same name. In this example, name is expected to be a property of the object being serialized:

classMovieSerializerincludeFastJsonapi::ObjectSerializerattribute:nameend

Custom attributes that must be serialized but do not exist on the model can be declared using Ruby block syntax:

classMovieSerializerincludeFastJsonapi::ObjectSerializerattributes:name,:yearattribute:name_with_yeardo |object|
"#{object.name} (#{object.year})"endend

The block syntax can also be used to override the property on the object:

classMovieSerializerincludeFastJsonapi::ObjectSerializerattribute:namedo |object|
"#{object.name} Part 2"endend

Attributes can also use a different name by passing the original method or accessor with a proc shortcut:

classMovieSerializerincludeFastJsonapi::ObjectSerializerattributes:nameattribute:released_in_year, &:yearend

Links Per Object

Links are defined in FastJsonapi using the link method. By default, links are read directly from the model property of the same name. In this example, public_url is expected to be a property of the object being serialized.

You can configure the method to use on the object for example a link with key self will get set to the value returned by a method called url on the movie object.

You can also use a block to define a url as shown in custom_url. You can access params in these blocks as well as shown in personalized_url

classMovieSerializerincludeFastJsonapi::ObjectSerializerlink:public_urllink:self,:urllink:custom_urldo |object|
"http://movies.com/#{object.name}-(#{object.year})"endlink:personalized_urldo |object,params|
"http://movies.com/#{object.name}-#{params[:user].reference_code}"endend

Links on a Relationship

You can specify relationship links by using the links: option on the serializer. Relationship links in JSON API are useful if you want to load a parent document and then load associated documents later due to size constraints (see related resource links)

classMovieSerializerincludeFastJsonapi::ObjectSerializerhas_many:actors,links: {self: :url,related: ->(object){"https://movies.com/#{object.id}/actors"}}end

This will create a self reference for the relationship, and a related link for loading the actors relationship later. NB: This will not automatically disable loading the data in the relationship, you'll need to do that using the lazy_load_data option:

has_many:actors,lazy_load_data: true,links: {self: :url,related: ->(object){"https://movies.com/#{object.id}/actors"}}

Meta Per Resource

For every resource in the collection, you can include a meta object containing non-standard meta-information about a resource that can not be represented as an attribute or relationship.

classMovieSerializerincludeFastJsonapi::ObjectSerializermetado |movie|
{years_since_release: Date.current.year - movie.year}endend

Compound Document

Support for top-level and nested included associations through options[:include].

options={}options[:meta]={total: 2}options[:links]={self: '...',next: '...',prev: '...'}options[:include]=[:actors,:'actors.agency',:'actors.agency.state']MovieSerializer.new([movie,movie],options).serialized_json

Collection Serialization

options[:meta]={total: 2}options[:links]={self: '...',next: '...',prev: '...'}hash=MovieSerializer.new([movie,movie],options).serializable_hashjson_string=MovieSerializer.new([movie,movie],options).serialized_json

Control Over Collection Serialization

You can use is_collection option to have better control over collection serialization.

If this option is not provided or nil autedetect logic is used to try understand if provided resource is a single object or collection.

Autodetect logic is compatible with most DB toolkits (ActiveRecord, Sequel, etc.) but cannot guarantee that single vs collection will be always detected properly.

options[:is_collection]

was introduced to be able to have precise control this behavior

• nil or not provided: will try to autodetect single vs collection (please, see notes above)
• true will always treat input resource as collection
• false will always treat input resource as single object

Caching

Requires a cache_key method be defined on model:

classMovieSerializerincludeFastJsonapi::ObjectSerializerset_type:movie# optionalcache_optionsenabled: true,cache_length: 12.hoursattributes:name,:yearend

Params

In some cases, attribute values might require more information than what is available on the record, for example, access privileges or other information related to a current authenticated user. The options[:params] value covers these cases by allowing you to pass in a hash of additional parameters necessary for your use case.

Leveraging the new params is easy, when you define a custom attribute or relationship with a block you opt-in to using params by adding it as a block parameter.

classMovieSerializerincludeFastJsonapi::ObjectSerializerattributes:name,:yearattribute:can_view_earlydo |movie,params|
# in here, params is a hash containing the `:current_user` keyparams[:current_user].is_employee? ? true : falseendbelongs_to:primary_agentdo |movie,params|
# in here, params is a hash containing the `:current_user` keyparams[:current_user].is_employee? ? true : falseendend# ...current_user=User.find(cookies[:current_user_id])serializer=MovieSerializer.new(movie,{params: {current_user: current_user}})serializer.serializable_hash

Custom attributes and relationships that only receive the resource are still possible by defining the block to only receive one argument.

Conditional Attributes

Conditional attributes can be defined by passing a Proc to the if key on the attribute method. Return true if the attribute should be serialized, and false if not. The record and any params passed to the serializer are available inside the Proc as the first and second parameters, respectively.

classMovieSerializerincludeFastJsonapi::ObjectSerializerattributes:name,:yearattribute:release_year,if: Proc.new{ |record|
# Release year will only be serialized if it's greater than 1990record.release_year > 1990}attribute:director,if: Proc.new{ |record,params|
# The director will be serialized only if the :admin key of params is trueparams && params[:admin] == true}end# ...current_user=User.find(cookies[:current_user_id])serializer=MovieSerializer.new(movie,{params: {admin: current_user.admin?}})serializer.serializable_hash

Conditional Relationships

Conditional relationships can be defined by passing a Proc to the if key. Return true if the relationship should be serialized, and false if not. The record and any params passed to the serializer are available inside the Proc as the first and second parameters, respectively.

classMovieSerializerincludeFastJsonapi::ObjectSerializer# Actors will only be serialized if the record has any associated actorshas_many:actors,if: Proc.new{ |record| record.actors.any?}# Owner will only be serialized if the :admin key of params is truebelongs_to:owner,if: Proc.new{ |record,params| params && params[:admin] == true}end# ...current_user=User.find(cookies[:current_user_id])serializer=MovieSerializer.new(movie,{params: {admin: current_user.admin?}})serializer.serializable_hash

Sparse Fieldsets

Attributes and relationships can be selectively returned per record type by using the fields option.

classMovieSerializerincludeFastJsonapi::ObjectSerializerattributes:name,:yearendserializer=MovieSerializer.new(movie,{fields: {movie: [:name]}})serializer.serializable_hash

Using helper methods

You can mix-in code from another ruby module into your serializer class to reuse functions across your app.

Since a serializer is evaluated in a the context of a class rather than an instance of a class, you need to make sure that your methods act as class methods when mixed in.

Using ActiveSupport::Concern

moduleAvatarHelperextendActiveSupport::Concernclass_methodsdodefavatar_url(user)user.image.urlendendendclassUserSerializerincludeFastJsonapi::ObjectSerializerincludeAvatarHelper# mixes in your helper method as class methodset_type:userattributes:name,:emailattribute:avatardo |user|
avatar_url(user)endend

Using Plain Old Ruby

moduleAvatarHelperdefavatar_url(user)user.image.urlendendclassUserSerializerincludeFastJsonapi::ObjectSerializerextendAvatarHelper# mixes in your helper method as class methodset_type:userattributes:name,:emailattribute:avatardo |user|
avatar_url(user)endend

Customizable Options

Option	Purpose	Example
set_type	Type name of Object	set_type :movie
key	Key of Object	belongs_to :owner, key: :user
set_id	ID of Object	set_id :owner_id or ```set_id {
cache_options	Hash to enable caching and set cache length	cache_options enabled: true, cache_length: 12.hours, race_condition_ttl: 10.seconds
id_method_name	Set custom method name to get ID of an object (If block is provided for the relationship, id_method_name is invoked on the return value of the block instead of the resource object)	has_many :locations, id_method_name: :place_ids
object_method_name	Set custom method name to get related objects	has_many :locations, object_method_name: :places
record_type	Set custom Object Type for a relationship	belongs_to :owner, record_type: :user
serializer	Set custom Serializer for a relationship	has_many :actors, serializer: :custom_actor or has_many :actors, serializer: MyApp::Api::V1::ActorSerializer
polymorphic	Allows different record types for a polymorphic association	has_many :targets, polymorphic: true
polymorphic	Sets custom record types for each object class in a polymorphic association	has_many :targets, polymorphic: { Person => :person, Group => :group }

Instrumentation

fast_jsonapi also has builtin Skylight integration. To enable, add the following to an initializer:

require'fast_jsonapi/instrumentation/skylight'

Skylight relies on ActiveSupport::Notifications to track these two core methods. If you would like to use these notifications without using Skylight, simply require the instrumentation integration:

require'fast_jsonapi/instrumentation'

The two instrumented notifcations are supplied by these two constants:

• FastJsonapi::ObjectSerializer::SERIALIZABLE_HASH_NOTIFICATION
• FastJsonapi::ObjectSerializer::SERIALIZED_JSON_NOTIFICATION

It is also possible to instrument one method without the other by using one of the following require statements:

require'fast_jsonapi/instrumentation/serializable_hash'require'fast_jsonapi/instrumentation/serialized_json'

Same goes for the Skylight integration:

require'fast_jsonapi/instrumentation/skylight/normalizers/serializable_hash'require'fast_jsonapi/instrumentation/skylight/normalizers/serialized_json'

Contributing

Please see contribution check for more details on contributing

Running Tests

We use RSpec for testing. We have unit tests, functional tests and performance tests. To run tests use the following command:

rspec

To run tests without the performance tests (for quicker test runs):

rspec spec --tag ~performance:true

To run tests only performance tests:

rspec spec --tag performance:true