Руководство по Ruby on Rails: Active Record: базовые ассоциации

Ruby on Rails Guides: Active Record: Association basics

A Guide to Active Record Associations
=====================================

This guide covers the association features of Active Record. By referring to this guide, you will be able to:

* Declare associations between Active Record models
* Understand the various types of Active Record associations
* Use the methods added to your models by creating associations

== Why Associations?

Why do we need associations between models? Because they make common operations simpler and easier in your code. For example, consider a simple Rails application that includes a model for customers and a model for orders. Each customer can have many orders. Without associations, the model declarations would look like this:

[source, ruby]
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class Customer < ActiveRecord::Base
end

class Order < ActiveRecord::Base
end
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Now, suppose we wanted to add a new order for an existing customer. We'd need to do something like this:

[source, ruby]
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@order = Order.create(:order_date => Time.now, :customer_id => @customer.id)
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Or consider deleting a customer, and ensuring that all of its orders get deleted as well:

[source, ruby]
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@orders = Order.find_by_customer_id(@customer.id)
@orders.each do |order|
order.destroy
end
@customer.destroy
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With Active Record associations, we can streamline these - and other - operations by declaratively telling Rails that there is a connection between the two models. Here's the revised code for setting up customers and orders:

[source, ruby]
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class Customer < ActiveRecord::Base
has_many :orders
end

class Order < ActiveRecord::Base
belongs_to :customer
end
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