Working With Rails

Piggy Back

Type Aware Piggy Backed Queries for Rails

This plugin makes it possible to piggy back attributes from a has_one or belongs_to association to the records retrieved on a AR::Base.find query.

Usage

Writing

piggy_back :user_name, :user, :name, :phone

or

piggy_back :user_name, :from => :user, :attributes => [:name, :phone]

will add a user_name and a user_phone method to the current class, if :user has been defined as a has_one or belongs_to association. The generated method will return the correctly type cast value of @attributes[‘user_name’], if the attribute has been retrieved by a corresponding find, for example

find :all, :piggy => :user_name, :limit => 20

or simply call user.name if no attribute user_name is present.

You can attach all content columns of the associated class using

piggy_back :all_of_user, :user

or

piggy_back :all_of_user, :from => :user, :attributes => :*

This will define read methods for all content columns of the user association (not recommended).

More than one piggy back is accepted by the piggy option given to find:

find :all, :piggy => [:user_name, :contract_name]

will retrieve attribute name from association contract along with attribute name from user, provided :contract_name has been declared as a piggy back as well:

piggy_back :contract_name, :contract, :name

This also works for finds constructed from associations. So

article.comments.find(:piggy => :user_name)

will retrieve all comments for article and attach comment.user.name to the retrieved comments.

By default, the prefix for the generated reader methods is derived from the association name. You can override this by passing a :prefix option to the piggy back declaration.

piggy_back :user_name, :user, :name, :phone, :prefix => :usr

will generate reader methods usr_name and usr_phone.

Preliminary hack

For now, piggy back will also work with has_many and has_many :through associations. This is only useful if the associated query is known to return a single value.

This feature will likely be removed once rails supports has_one :through associations.

Additional Information

See http://railsexpress.de/blog/articles/2006/05/29/simpler-piggy-backing.

Or just follow a Jedi’s advice: “Use the source, Luke!”

NOTE: This description has been extracted from the Plugin README and so the formatting may need updating to make browser friendly