PostgresExt-Serializers

This Gem patches the ArraySerializer in Active Model Serializers to offload JSON serialization to PostgreSQL, which is much faster and more memory efficient than serialization in Ruby.

Instead of instantiating lots of ActiveRecord models, which are then serialized to a hash using ActiveModel Serializers and finally converted to JSON, this Gem builds the entire JSON in the database and returns it as a single string that can be passed through to the client unmodified.

How does it work?

You can read Avoid Rails When Generating JSON responses with PostgreSQL by Dan McClain on the DockYard Blog or watch a YouTube video of his Postgres Open 2014 Talk Using PostgreSQL, not Rails, to make Rails faster (Slides) to understand how this Gem works under the hood.

Supported Versions

This gem currently only works with the older active_model_serializers 0.8.x and activerecord 4.0/4.1/4.2. For activerecord 4.2 support you need at least postgres_ext version 2.4.0.

You must be using at least Postgres 9.2, but 9.4 or later is recommended.

Support for newer AMS versions might be added in the future.

Looking for help?

If it is a bug please open an issue on Github. If you need help using the gem please ask the question on Stack Overflow. Be sure to tag the question with DockYard so we can find it.

Installation

Add this line to your application's Gemfile:

gem 'postgres_ext-serializers'

And then execute:

$ bundle

Or install it yourself as:

$ gem install postgres_ext-serializers

Usage

Just require 'postgres_ext/serializers' and use ActiveModel::Serializers as you normally would! Postgres_ext-serializers will take over anytime you try to serialize an ActiveRecord::Relation.

Methods in Serializers and Models

If you are using methods to compute properties for your JSON responses in your models or serializers, postgres_ext-serializers will try to discover a SQL version of this call by looking for a class method with the same name and the suffix __sql. Here's an example:

class MyModel < ActiveRecord::Base
  def full_name
    "#{object.first_name} #{object.last_name}"
  end

  def self.full_name__sql
    "first_name || ' ' || last_name"
  end
end

class MySerializer < ActiveModel::Serializer
  def full_name
    "#{object.first_name} #{object.last_name}"
  end

  def full_name__sql
    "first_name || ' ' || last_name"
  end
end

There is no instance of MyModel created so sql computed properties needs to be a class method. Right now, this string is used as a SQL literal, so be sure to not use untrusted values in the return value.

Note: Postgres date, timestamp or timestamptz format

Postgres 9.2 and 9.3 by default renders dates according to the current DateStyle Postgres setting, but many JSON processors require dates to be in ISO 8601 format e.g. Firefox or Internet Explorer will parse string as invalid date with default DateStyle setting. Postgres 9.4 onwards now uses ISO 8601 for JSON serialization instead.

Developing

To work on postgres_ext-serializers locally, follow these steps:

Run bundle install, this will install (almost) all the development dependencies
Run gem install byebug (not a declared dependency to not break CI)
Run bundle exec rake setup, this will set up the .env file necessary to run the tests and set up the database
Run bundle exec rake db:create, this will create the test database
Run bundle exec rake db:migrate, this will set up the database tables required by the test
Run BUNDLE_GEMFILE='gemfiles/Gemfile.activerecord-4.2.x' bundle install --quiet to create the Gemfile.lock.
Run bundle exec rake test:all to run tests against all supported versions of Active Record (currently 4.0.x, 4.1.x, 4.2.x)