Custom field example for Ruby on Rails with Activerecord & PostgreSQL & Metaprogramming. Example: https://github.com/lab2023/postgresql_jsonb_ransack_rails_5 Demo: https://rails-custom-field-ransack.herokuapp.com

ruby_custom_field_with_postgresql_and_metaprogramming.rb

begin
  require 'bundler/inline'
rescue LoadError => e
  $stderr.puts 'Bundler version 1.10 or later is required. Update your Bundler'
  raise e
end

gemfile(true) do
  source 'https://rubygems.org'
  gem 'activerecord', '5.1.3'
  gem 'pg', '~> 0.18.4'
end

# Require gems
require 'active_record'
require 'minitest/autorun'
require 'logger'

# DB configurations
db_config = {
  adapter: 'postgresql',
  host: 'localhost',
  database: 'custom_field',
  username: 'postgres'
}
admin_config = {
  database: 'postgres',
  schema_search_path: 'public'
}
db_config_admin = db_config.merge(admin_config)
ActiveRecord::Base.logger = Logger.new(STDOUT)
ActiveRecord::Base.establish_connection(db_config_admin)
ActiveRecord::Base.connection.drop_database(db_config[:database])
ActiveRecord::Base.connection.create_database(db_config[:database])

# Migrations
ActiveRecord::Schema.define do
  create_table :posts, force: true do |t|
    t.integer :status, default: 0
    t.jsonb :metadata, default: {}, null: false
  end
  add_index :posts, :metadata, using: :gin
end

# Helpers
def custom_field_method(field)
  "metadata_#{field}"
end

# Models
class Post < ActiveRecord::Base
end

# Custom fields
# You can store this information in database as jsonb datatype
POST_FIELDS = {
  title: {
    name: 'Title',
    validations: [],
    input_type: 'string'
  },
  description: {
    name: 'Description',
    validations: [],
    input_type: 'string'
  },
  number: {
    name: 'Number',
    validations: [:number],
    input_type: 'number'
  }
}.freeze

POST_FIELDS.each do |field, options|
  field = field.to_s
  Post.class_eval do
    method = custom_field_method(field)
    options[:validations].each do |validation|
      validates_numericality_of method if validation == :number
    end
  end

  Post.instance_eval do
    method = custom_field_method(field)
    define_method "#{method}=" do |val|
      metadata[field] = val
    end

    define_method method do
      metadata[field]
    end
  end
end

# Tests
class PostTest < Minitest::Test
  def test_metadata_fields
    post = Post.new(
      metadata_title: 'title',
      metadata_description: 'description',
      metadata_number: 1
    )
    assert_equal true, post.save
    assert_equal 'title', post.metadata_title
    assert_equal 'description', post.metadata_description
  end

  def test_valid_metadata_number
    post = Post.new(metadata_number: 1)
    assert_equal true, post.save
    assert_equal true, post.valid?
  end

  def test_valid_negative_metadata_number
    post = Post.new(metadata_number: -122)
    assert_equal true, post.save
    assert_equal true, post.metadata_number.is_a?(Integer)

    post = Post.new(metadata_number: -122.33)
    assert_equal true, post.save
    assert_equal true, post.metadata_number.is_a?(Float)
  end

  def test_invalid_metadata_number
    post = Post.new(metadata_number: 'title')
    assert_equal false, post.save
    assert_equal true, post.errors[:metadata_number].any?
  end
end