A fast JSON:API serializer for Ruby Objects.
Previously this project was called fast_jsonapi, we forked the project and renamed it to jsonapi/serializer in order to keep it alive.
We would like to thank the Netflix team for the initial work and to all our contributors and users for the continuous support!
We compare serialization times with ActiveModelSerializer and alternative
implementations as part of performance tests available at
jsonapi-serializer/comparisons.
We want to ensure that with every
change on this library, serialization time stays significantly faster than
the performance provided by the alternatives. Please read the performance
article in the docs folder for any questions related to methodology.
- Declaration syntax similar to Active Model Serializer
- Support for
belongs_to,has_manyandhas_one - Support for compound documents (included)
- Optimized serialization of compound documents
- Caching
Add this line to your application's Gemfile:
gem 'jsonapi-serializer'Execute:
$ bundle installYou 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
class Movie
attr_accessor :id, :name, :year, :actor_ids, :owner_id, :movie_type_id
endclass MovieSerializer
include JSONAPI::Serializer
set_type :movie # optional
set_id :owner_id # optional
attributes :name, :year
has_many :actors
belongs_to :owner, record_type: :user
belongs_to :movie_type
endmovie = Movie.new
movie.id = 232
movie.name = 'test movie'
movie.actor_ids = [1, 2, 3]
movie.owner_id = 3
movie.movie_type_id = 1
movie
movies =
2.times.map do |i|
m = Movie.new
m.id = i + 1
m.name = "test movie #{i}"
m.actor_ids = [1, 2, 3]
m.owner_id = 3
m.movie_type_id = 1
m
endhash = MovieSerializer.new(movie).serializable_hashjson_string = MovieSerializer.new(movie).serializable_hash.to_json{
"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"
}
}
}
}
}
By default fast_jsonapi will try to figure the type based on the name of the serializer class. For example class MovieSerializer will automatically have a type of :movie. If your serializer class name does not follow this format, you have to manually state the set_type at the serializer.
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
class MovieSerializer
include JSONAPI::Serializer
# Available options :camel, :camel_lower, :dash, :underscore(default)
set_key_transform :camel
endHere 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 are defined 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:
class MovieSerializer
include JSONAPI::Serializer
attribute :name
endCustom attributes that must be serialized but do not exist on the model can be declared using Ruby block syntax:
class MovieSerializer
include JSONAPI::Serializer
attributes :name, :year
attribute :name_with_year do |object|
"#{object.name} (#{object.year})"
end
endThe block syntax can also be used to override the property on the object:
class MovieSerializer
include JSONAPI::Serializer
attribute :name do |object|
"#{object.name} Part 2"
end
endAttributes can also use a different name by passing the original method or accessor with a proc shortcut:
class MovieSerializer
include JSONAPI::Serializer
attributes :name
attribute :released_in_year, &:year
endLinks are defined 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
class MovieSerializer
include JSONAPI::Serializer
link :public_url
link :self, :url
link :custom_url do |object|
"https://movies.com/#{object.name}-(#{object.year})"
end
link :personalized_url do |object, params|
"https://movies.com/#{object.name}-#{params[:user].reference_code}"
end
endYou 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)
class MovieSerializer
include JSONAPI::Serializer
has_many :actors, links: {
self: :url,
related: -> (object) {
"https://movies.com/#{object.id}/actors"
}
}
endRelationship links can also be configured to be defined as a method on the object.
has_many :actors, links: :actor_relationship_linksThis 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"
}
}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.
class MovieSerializer
include JSONAPI::Serializer
meta do |movie|
{
years_since_release: Date.current.year - movie.year
}
end
endYou can specify relationship meta by using the meta: option on the serializer. Relationship meta in JSON API is useful if you wish to provide non-standard meta-information about the relationship.
Meta can be defined either by passing a static hash or by using Proc to the meta key. In the latter case, the record and any params passed to the serializer are available inside the Proc as the first and second parameters, respectively.
class MovieSerializer
include JSONAPI::Serializer
has_many :actors, meta: Proc.new do |movie_record, params|
{ count: movie_record.actors.length }
end
endSupport 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(movies, options).serializable_hash.to_jsonoptions[:meta] = { total: 2 }
options[:links] = {
self: '...',
next: '...',
prev: '...'
}
hash = MovieSerializer.new(movies, options).serializable_hash
json_string = MovieSerializer.new(movies, options).serializable_hash.to_jsonYou can use is_collection option to have better control over collection serialization.
If this option is not provided or nil autodetect 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
nilor not provided: will try to autodetect single vs collection (please, see notes above)truewill always treat input resource as collectionfalsewill always treat input resource as single object
To enable caching, use cache_options store: <cache_store>:
class MovieSerializer
include JSONAPI::Serializer
# use rails cache with a separate namespace and fixed expiry
cache_options store: Rails.cache, namespace: 'jsonapi-serializer', expires_in: 1.hour
endstore is required can be anything that implements a
#fetch(record, **options, &block) method:
recordis the record that is currently serializedoptionsis everything that was passed tocache_optionsexceptstore, so it can be everyhing the cache store supports&blockshould be executed to fetch new data if cache is empty
So for the example above it will call the cache instance like this:
Rails.cache.fetch(record, namespace: 'jsonapi-serializer', expires_in: 1.hour) { ... }If caching is enabled and fields are provided to the serializer, the fieldset will be appended to the cache key's namespace.
For example, given the following serializer definition and instance:
class ActorSerializer
include JSONAPI::Serializer
attributes :first_name, :last_name
cache_options store: Rails.cache, namespace: 'jsonapi-serializer', expires_in: 1.hour
end
serializer = ActorSerializer.new(actor, { fields: { actor: [:first_name] } })The following cache namespace will be generated: 'jsonapi-serializer-fieldset:first_name'.
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 id, attribute or relationship with a block you opt-in to using params by adding it as a block parameter.
class MovieSerializer
include JSONAPI::Serializer
set_id do |movie, params|
# in here, params is a hash containing the `:admin` key
params[:admin] ? movie.owner_id : "movie-#{movie.id}"
end
attributes :name, :year
attribute :can_view_early do |movie, params|
# in here, params is a hash containing the `:current_user` key
params[:current_user].is_employee? ? true : false
end
belongs_to :primary_agent do |movie, params|
# in here, params is a hash containing the `:current_user` key
params[:current_user].is_employee? ? true : false
end
end
# ...
current_user = User.find(cookies[:current_user_id])
serializer = MovieSerializer.new(movie, {params: {current_user: current_user}})
serializer.serializable_hashCustom attributes and relationships that only receive the resource are still possible by defining the block to only receive one argument.
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.
class MovieSerializer
include JSONAPI::Serializer
attributes :name, :year
attribute :release_year, if: Proc.new { |record|
# Release year will only be serialized if it's greater than 1990
record.release_year > 1990
}
attribute :director, if: Proc.new { |record, params|
# The director will be serialized only if the :admin key of params is true
params && params[:admin] == true
}
# Custom attribute `name_year` will only be serialized if both `name` and `year` fields are present
attribute :name_year, if: Proc.new { |record|
record.name.present? && record.year.present?
} do |object|
"#{object.name} - #{object.year}"
end
end
# ...
current_user = User.find(cookies[:current_user_id])
serializer = MovieSerializer.new(movie, { params: { admin: current_user.admin? }})
serializer.serializable_hashConditional 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.
class MovieSerializer
include JSONAPI::Serializer
# Actors will only be serialized if the record has any associated actors
has_many :actors, if: Proc.new { |record| record.actors.any? }
# Owner will only be serialized if the :admin key of params is true
belongs_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_hashIn many cases, the relationship can automatically detect the serializer to use.
class MovieSerializer
include JSONAPI::Serializer
# resolves to StudioSerializer
belongs_to :studio
# resolves to ActorSerializer
has_many :actors
endAt other times, such as when a property name differs from the class name, you may need to explicitly state the serializer to use. You can do so by specifying a different symbol or the serializer class itself (which is the recommended usage):
class MovieSerializer
include JSONAPI::Serializer
# resolves to MovieStudioSerializer
belongs_to :studio, serializer: :movie_studio
# resolves to PerformerSerializer
has_many :actors, serializer: PerformerSerializer
endFor more advanced cases, such as polymorphic relationships and Single Table Inheritance, you may need even greater control to select the serializer based on the specific object or some specified serialization parameters. You can do by defining the serializer as a Proc:
class MovieSerializer
include JSONAPI::Serializer
has_many :actors, serializer: Proc.new do |record, params|
if record.comedian?
ComedianSerializer
elsif params[:use_drama_serializer]
DramaSerializer
else
ActorSerializer
end
end
endAttributes and relationships can be selectively returned per record type by using the fields option.
class MovieSerializer
include JSONAPI::Serializer
attributes :name, :year
end
serializer = MovieSerializer.new(movie, { fields: { movie: [:name] } })
serializer.serializable_hashYou 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.
module AvatarHelper
extend ActiveSupport::Concern
class_methods do
def avatar_url(user)
user.image.url
end
end
end
class UserSerializer
include JSONAPI::Serializer
include AvatarHelper # mixes in your helper method as class method
set_type :user
attributes :name, :email
attribute :avatar do |user|
avatar_url(user)
end
endmodule AvatarHelper
def avatar_url(user)
user.image.url
end
end
class UserSerializer
include JSONAPI::Serializer
extend AvatarHelper # mixes in your helper method as class method
set_type :user
attributes :name, :email
attribute :avatar do |user|
avatar_url(user)
end
end| 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 { |record, params| params[:admin] ? record.id : "#{record.name.downcase}-#{record.id}" } |
| cache_options | Hash with store to enable caching and optional further cache options | cache_options store: ActiveSupport::Cache::MemoryStore.new, expires_in: 5.minutes |
| 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, has_many :actors, serializer: MyApp::Api::V1::ActorSerializer, or has_many :actors, serializer -> (object, params) { (return a serializer class) } |
| 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 } |
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 notifications are supplied by these two constants:
FastJsonapi::ObjectSerializer::SERIALIZABLE_HASH_NOTIFICATIONFastJsonapi::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'The project has and requires unit tests, functional tests and performance tests. To run tests use the following command:
rspecPlease follow the instructions we provide as part of the issue and pull request creation processes.
This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.