hydra_attribute

Wiki | RDoc

hydra_attribute is an implementation of EAV (Entity-Attribute-Value) pattern for ActiveRecord models. It allows to create or remove attributes in runtime. Also each record may have different sets of attributes, for example: Product with ID 1 can have different set of attributes than Product with ID 2.

Notice

Until the first major version is released:

• each new minor version doesn't guarantee back compatibility with previous one
• gem isn't stable enough for using in production

Requirements

• ruby >= 1.9.2
• active_record ~> 3.2

Installation

Add the following line to Gemfile:

gem 'hydra_attribute'

and run bundle install from your shell.

Then we should generate our migration:

rails generate migration create_hydra_attributes

The content should be:

class CreateHydraAttributeTables < ActiveRecord::Migration
  def up
    create_hydra_entity :products do |t|
      # add here all other columns that should be in the entity table
      t.timestamps
    end
  end
      
  def down
    drop_hydra_entity :products
  end
end

or if we have the entity table already

class CreateHydraAttributeTables < ActiveRecord::Migration
  def up
    migrate_to_hydra_entity :products
  end
      
  def down
    rollback_from_hydra_entity :products
  end
end

Usage

Create model

rails generate model Product --migration=false
rake db:migrate

and include HydraAttribute::ActiveRecord to Product class

class Product < ActiveRecord::Base
  include HydraAttribute::ActiveRecord
end

Create hydra attributes

Product.hydra_attributes.create(name: 'color', backend_type: 'string', default_value: 'green')
Product.hydra_attributes.create(name: 'title', backend_type: 'string')
Product.hydra_attributes.create(name: 'total', backend_type: 'integer', default_value: 1)

Creating method accepts the following options:

• name. The required parameter. Any string is allowed.

• backend_type. The required parameter. One of the following strings is allowed: string, text, integer, float, boolean and datetime.

• default_value. The optional parameter. Any value is allowed. nil is default.

• white_list. The optional parameter. Should be true or false. false is default. If white_list: true is passed, this attribute will be added to white list and will be allowed for mass-assignment. This parameter is in black list for creation by default so if you want to pass it, you have to pass the role as: :admin too.

    Product.hydra_attributes.create({name: 'title', backend_type: 'string', white_list: true}, as: :admin)

Create records

Product.create
#<Product id: 1, hydra_set_id: nil, created_at: ..., updated_at: ..., color: "green", title: nil, total: 1>
Product.create(color: 'red', title: 'toy')
#<Product id: 2, hydra_set_id: nil, created_at: ..., updated_at: ..., color: "red", title: "toy", total: 1>
Product.create(title: 'book', total: 2)
#<Product id: 3, hydra_set_id: nil, created_at: ..., updated_at: ..., color: "green", title: "book", total: 2>

Add new hydra attribute in runtime

Product.hydra_attributes.create(name: 'price', backend_type: 'float', default_value: 0.0)
Product.create(title: 'car', price: 2.50)
#<Product id: 4, hydra_set_id: nil, created_at: ..., updated_at: ..., color: "green", title: "car", total: 2, price: 2.5>

Create hydra set

Hydra set allows to set the unique attribute list for each entity.

hydra_set = Product.hydra_sets.create(name: 'Default')
hydra_set.hydra_attributes = Product.hydra_attributes.where(name: %w(color title price))

Product.create(color: 'black', title: 'ipod', price: 49.95, total: 5) do |product|
  product.hydra_set_id = hydra_set.id
end
#<Product id: 5, hydra_set_id: 1, created_at: ..., updated_at: ..., color: "black", title: "ipod", price: 49.95>

Notice: the total attribute has been skipped because it doesn't exist in hydra set.

Obtain data

Product.where(color: 'red')
# [#<Product id: 2, hydra_set_id: nil, created_at: ..., updated_at: ..., color: "red", title: "toy", price: 0.0, total: 1>]
Product.where(color: 'green', price: nil)
# [
    #<Product id: 1, hydra_set_id: nil, created_at: ..., updated_at: ..., color: "green", title: nil, price: 0.0, total: 1>,
    #<Product id: 3, hydra_set_id: nil, created_at: ..., updated_at: ..., color: "green", title: "book", price: 0.0, total: 2>
# ]

Notice: the attribute price has been added in runtime. Records that had been created before this attribute don't have it therefore they satisfy the following condition: where(price: nil)

Order data

Product.order(:color, :title).first
#<Product id: 5, hydra_set_id: 1, created_at: ..., updated_at: ..., color: "black", title: "ipod", price: 49.95>
Product.order(:color, :title).reverse_order.first
#<Product id: 2, hydra_set_id: nil, created_at: ..., updated_at: ..., color: "red", title: "toy", price: 0.0, total: 1>

Select concrete attributes

Product.select([:color, :title])
# [
    #<Product id: 1, hydra_set_id: nil, color: "green", title: nil>,
    #<Product id: 2, hydra_set_id: nil, color: "red", title: "toy">,
    #<Product id: 3, hydra_set_id: nil, color: "green", title: "book">,
    #<Product id: 4, hydra_set_id: nil, color: "green", title: "car">,
    #<Product id: 5, hydra_set_id: 1, color: "black", title: "ipod">
# ] 

Notice: id and hydra_set_id attributes are forcibly added because they are important for correct work.

Group by attribute

Product.group(:color).count
# {"black"=>1, "green"=>3, "red"=>1}

Wiki Docs

• Create migration
• Create attributes in runtime
• Create sets of attributes
• Query methods
• Database schema
• Helper methods
• Migrate from 0.3.2 to 0.4.0

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Added some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request