Use PostgreSQL JSONB fields to store foreign ids on your models.
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README.md

activerecord-json-associations

Gem Version

Use PostgreSQL JSONB fields to store association information of your models.

This gem was created as a solution to this task from EvilMartians.

Requirements:

  • PostgreSQL (>= 9.6)

Usage

One-to-one and One-to-many associations

You can store all foreign keys of your model in one JSONB column, without having to create multiple columns:

class Profile < ActiveRecord::Base
  # Setting additional :store option on :belongs_to association
  # enables saving of foreign ids in :extra JSONB column 
  belongs_to :user, store: :extra
end

class SocialProfile < ActiveRecord::Base
  belongs_to :user, store: :extra
end

class User < ActiveRecord::Base
  # Parent model association needs to specify :foreign_store
  # for associations with JSONB storage
  has_one :profile, foreign_store: :extra
  has_many :social_profiles, foreign_store: :extra
end

Foreign keys for association on one model have to be unique, even if they use different store column.

You can also use add_references in your migration to add JSONB column and index for it (if index: true option is set):

add_reference :profiles, :users, store: :extra, index: true

Many-to-many associations

You can also use JSONB columns on 2 sides of a HABTM association. This way you won't have to create a join table.

class Label < ActiveRecord::Base
  # extra['user_ids'] will store associated user ids
  has_and_belongs_to_many :users, store: :extra
end

class User < ActiveRecord::Base
  # extra['label_ids'] will store associated label ids
  has_and_belongs_to_many :labels, store: :extra
end

Performance

Compared to regular associations, fetching models associated via JSONB column has no drops in performance.

Getting the count of connected records is ~35% faster with associations via JSONB (tested on associations with up to 10 000 connections).

Adding new connections is slightly faster with JSONB, for scopes up to 500 records connected to another record (total count of records in the table does not matter that much. If you have more then ~500 records connected to one record on average, and you want to add new records to the scope, JSONB associations will be slower then traditional:

JSONB HAMTB is slower on adding associations

On the other hand, unassociating models from a big amount of associated models if faster with JSONB HABTM as the associations count grows:

JSONB HAMTB is faster on removing associations

Installation

Add this line to your application's Gemfile:

gem 'activerecord-jsonb-associations'

And then execute:

$ bundle install

Developing

To setup development environment, just run:

$ bin/setup

To run specs:

$ bundle exec rspec

To run benchmarks (that will take a while):

$ bundle exec rake benchmarks:habtm

License

The gem is available as open source under the terms of the MIT License.