Attribute Depends Calculator

The scenario of the gem is when you have an attribute on model that value depends of a calculation of other model's attribute which attribute's model related. AttributeDependsCalculator will help you solve the case

Requirements

Ruby 2.0+
Rails 4.0+

Installation

Add this line to your application's Gemfile:

gem 'attribute-depends-calculator'

And then execute:

$ bundle

Usage

Assume you have model order and order-item

class Order < ActiveRecord::Base
  has_many :order_items
  depend total_price: {order_items: :price}
end

class OrderItem < ActiveRecord::Base
  belongs_to :order
end

And you can

order = Order.first
order.total_price
#=> 100.0
order.order_items.pluck(:price)
#=> [50.0, 50.0]
order_item = order.order_items.first
order_item.update(price: 100)
order.reload.total_price
#=> 150.0

As above show the price of order automatically update when whatever order_items changes

Advanced

The options operator had two cateogries of value, the default value of the gem is expression sum

Operation

class Order < ActiveRecord::Base
  has_many :order_items
  depend total_price: {order_items: :price, operator: :+} # or :*
end

Expression

The following expression can be use to calculate the collection of depends attributes

sum

class Order < ActiveRecord::Base
  ...
  depend total_price: {order_items: :price, operator: :sum} # default
end

average

class Order < ActiveRecord::Base
  ...
  depend avg_price: {order_items: :price, operator: :average}
end

count

class Order < ActiveRecord::Base
  ...
  depend order_items_count: {order_items: :price, operator: :count}
end

minimum

class Order < ActiveRecord::Base
  ...
  depend min_price: {order_items: :price, operator: :minimum}
end

maximum

class Order < ActiveRecord::Base
  ...
  depend max_price: {order_items: :price, operator: :maximum}
end

Proc

Proc can be passing in operator option, and the only one params is the active reload of the depended relate Model

class Order < ActiveRecord::Base
  ...
  depend discount_price: {order_items: :price, operator: -> (items) { items.sum(:price) * discount } }
end

Contributing

Bug reports and pull requests are welcome on GitHub