JSONb Accessor

Adds typed jsonb backed fields as first class citizens to your ActiveRecord models. This gem is similar in spirit to HstoreAccessor, but the jsonb column in PostgreSQL has a few distinct advantages, mostly around nested documents and support for collections.

Table of Contents

• Installation
• Usage
• ActiveRecord Methods Generated for Fields
• Validations
• Single-Table Inheritance
• Scopes
• Migrations
• Dependencies
• Development
• Contributing

Installation

Add this line to your application's Gemfile:

gem "jsonb_accessor"

And then execute:

$ bundle install

Usage

First we must create a model which has a jsonb column available to store data into it:

class CreateProductsTable < ActiveRecord::Migration
  def change
    create_table :products do |t|
      t.jsonb :options
    end
  end
end

We can then declare the jsonb fields we wish to expose via the accessor:

class Product < ActiveRecord::Base
  jsonb_accessor(
    :options,
    :count, # => value type
    title: :string,
    id_value: :value,
    external_id: :integer,
    reviewed_at: :date_time
  )
end

JSONb Accessor accepts both untyped and typed key definitions. Untyped keys are treated as-is and no additional casting is performed. This allows the freedom of dynamic values alongside the power types, which is especially convenient when saving nested form attributes. Typed keys will be cast to their respective values using the same mechanism ActiveRecord uses to coerce standard attribute columns. It's as close to a real column as you can get and the goal is to keep it that way.

All untyped keys must be defined prior to typed columns. You can declare a typed column with type value for explicit dynamic behavior. For reference, the jsonb_accessor macro is defined thusly.

def jsonb_accessor(jsonb_attribute, *value_fields, **typed_fields)
  ...
end

There's quite a bit more to do do and document but we're excited to get this out there while we work on it some more.

ActiveRecord Methods Generated for Fields

class Product < ActiveRecord::Base
  jsonb_accessor :data, field: :string
end

• field
• field=
• field?
• field_changed?
• field_was
• field_change
• reset_field!
• restore_field!
• field_will_change!

Supported Types

The following types are supported:

• big_integer
• binary
• bit
• bit_varying
• boolean
• bytea
• cidr
• date
• date_time
• decimal
• decimal_without_scale
• enum
• float
• hstore
• inet
• integer
• json
• jsonb
• money
• point
• range
• specialized_string
• string
• text
• time
• unsigned_integer
• uuid
• value
• vector
• xml

Typed arrays are also supported by specifying :type_array (i.e. :float_array). :array is interpreted as an array of value types.

Support for nested types is also available but experimental at this point. If you must, you may try something like this for nested objects.

class Product < ActiveRecord::Base
  jsonb_accessor(
    :options,
    nested_object: { key: :integer }
  )
end

p = Product.new
p.nested_object.key = "10"
puts p.nested_object.key #=> 10

Validations

Because this gem promotes attributes nested into the JSON column to first level attributes, most validations should just work. We still have to add some testing and support around this feature but feel free to try and leave us feedback if they're not working as expected.

Single-Table Inheritance

One of the big issues with ActiveRecord single-table inheritance (STI) is sparse columns. Essentially, as sub-types of the original table diverge further from their parent more columns are left empty in a given table. Postgres' jsonb type provides part of the solution in that the values in an jsonb column does not impose a structure - different rows can have different values.

We set up our table with an jsonb field:

# db/migration/<timestamp>_create_players_table.rb
class CreateVehiclesTable < ActiveRecord::Migration
  def change
    create_table :vehicles do |t|
      t.string :make
      t.string :model
      t.integer :model_year
      t.string :type
      t.jsonb :data
    end
  end
end

And for our models:

# app/models/vehicle.rb
class Vehicle < ActiveRecord::Base
end

# app/models/vehicles/automobile.rb
class Automobile < Vehicle
  jsonb_accessor :data,
    axle_count: :integer,
    weight: :float
end

# app/models/vehicles/airplane.rb
class Airplane < Vehicle
  jsonb_accessor :data,
    engine_type: :string,
    safety_rating: :integer
end

From here any attributes specific to any sub-class can be stored in the jsonb column avoiding sparse data. Indices can also be created on individual fields in an jsonb column.

This approach was originally concieved by Joe Hirn in this blog post.

Scopes

JsonbAccessor currently supports several scopes. Let's say we have a class that looks like this:

class Product < ActiveRecord::Base
  jsonb_accessor :data,
    approved: :boolean,
    name: :string,
    price: :integer,
    previous_prices: :integer_array,
    reviewed_at: :date_time
end

General Scopes

<jsonb_field>_contains

Description: returns all records that contain matching attributes in the specified jsonb field.

product_1 = Product.create!(name: "foo", approved: true, reviewed_at: 3.days.ago)
product_2 = Product.create!(name: "bar", approved: true)
product_3 = Product.create!(name: "foo", approved: false)

Product.data_contains(name: "foo", approved: true) # => [product_1]

Note: when including an array attribute, the stored array and the array used for the query do not need to match exactly. For example, when queried with [1, 2], records that have arrays of [2, 1, 3] will be returned.

with_<jsonb_defined_field>

Description: returns all records with the given value in the field. This is defined for all jsonb_accessor defined fields. It's a convenience method that allows you to do Product.with_name("foo") instead of Product.data_contains(name: "foo").

product_1 = Product.create!(name: "foo")
product_2 = Product.create!(name: "bar")

Product.with_name("foo") # => [product_1]

Note: when including an array attribute, the stored array and the array used for the query do not need to match exactly. For example, when queried with [1, 2], records that have arrays of [2, 1, 3] will be returned.

Integer, Big Integer, Decimal, and Float Scopes

<jsonb_defined_field>_gt

Description: returns all records with a value that is greater than the argument.

product_1 = Product.create!(price: 10)
product_2 = Product.create!(price: 11)

Product.price_gt(10) # => [product_2]

<jsonb_defined_field>_gte

Description: returns all records with a value that is greater than or equal to the argument.

product_1 = Product.create!(price: 10)
product_2 = Product.create!(price: 11)
product_3 = Product.create!(price: 9)

Product.price_gte(10) # => [product_1, product_2]

<jsonb_defined_field>_lt

Description: returns all records with a value that is less than the argument.

product_1 = Product.create!(price: 10)
product_2 = Product.create!(price: 11)

Product.price_lt(11) # => [product_1]

<jsonb_defined_field>_lte

Description: returns all records with a value that is less than or equal to the argument.

product_1 = Product.create!(price: 10)
product_2 = Product.create!(price: 11)
product_3 = Product.create!(price: 12)

Product.price_lte(11) # => [product_1, product_2]

Boolean Scopes

is_<jsonb_defined_field>

Description: returns all records where the value is true.

product_1 = Product.create!(approved: true)
product_2 = Product.create!(approved: false)

Product.is_approved # => [product_1]

not_<jsonb_defined_field>

Description: returns all records where the value is false.

product_1 = Product.create!(approved: true)
product_2 = Product.create!(approved: false)

Product.not_approved # => [product_2]

Date, DateTime Scopes

<jsonb_defined_field>_before

Description: returns all records where the value is before the argument. Also supports JSON string arguments.

product_1 = Product.create!(reviewed_at: 3.days.ago)
product_2 = Product.create!(reviewed_at: 5.days.ago)

Product.reviewed_at_before(4.days.ago) # => [product_2]
Product.reviewed_at_before(4.days.ago.to_json) # => [product_2]

<jsonb_defined_field>_after

Description: returns all records where the value is after the argument. Also supports JSON string arguments.

product_1 = Product.create!(reviewed_at: 3.days.from_now)
product_2 = Product.create!(reviewed_at: 5.days.from_now)

Product.reviewed_at_after(4.days.from_now) # => [product_2]
Product.reviewed_at_after(4.days.from_now.to_json) # => [product_2]

Array Scopes

<jsonb_defined_fields>_contains

Description: returns all records where the value is contained in the array field.

product_1 = Product.create!(previous_prices: [3])
product_2 = Product.create!(previous_prices: [4, 5, 6])

Product.previous_prices_contains(5) # => [product_2]

Migrations

Coming soon...

jsonb supports GIN, GIST, btree and hash indexes over json column. We have plans to add migrations helpers for generating these indexes for you.

Dependencies

• ActiveRecord 4.2
• Postgres 9.4 (in order to use the jsonb column type).

Development

After checking out the repo, run bin/setup to install dependencies (make sure postgres is running first).

Run bin/console for an interactive prompt that will allow you to experiment.

rake will run Rubocop and the specs.

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Add tests and changes (run the tests with rake)
4. Commit your changes (git commit -am 'Add some feature')
5. Push to the branch (git push origin my-new-feature)
6. Create a new Pull Request