2009 07 21: Nested Attributes

Wolfram Arnold www.rubyfocus.biz Nested Attributes
CRUD
on multiple models
without crud

Associations
class Pirate < ActiveRecord::Base has_one :ship end
class Ship < ActiveRecord::Base belongs_to :pirate end

User Interface?
Form with pirate and ship fields
form_for :pirate do |pf| pf.text_field :catchphrase pf.fields_for :ship do |sf| sf.text_field :name end # params[pirate][ship] # Note: broken! end

Controller Interface?
def create @pirate = Pirate.new(params[:pirate]) @ship = Ship.new(params[:pirate][:ship]) @ship.pirate = @pirate if @pirate.save && @ship.save ... else # what about rollback? end end

Fat model/skinny controller
Logic in the model, not views/controllers
Assignments
class Pirate < ActiveRecord::Base def ship_attributes=(attrs) ... end end
Validations handled in model, incl. child models

Saving—when?
:autosave => true flag, new in Rails 2.3!
Automatically turned on for accepts_nested_attributes_for
Parent will save all children
New parent, modified children
Existing parent, new/modified children
As a transaction—rollback on validation failure
Cascaded error messages
Removes a lot of confusion
Demo

Web Service API
PirateController and ShipController?
Not advised if
Objects have a relationship, e.g. has_one association
Dependencies
Business logic rules/validations
Better single API with nested attributes
Simpler client code
Less network traffic

References
http://api.rubyonrails.org/classes/ActiveRecord/NestedAttributes/ClassMethods.html#M002132
http://github.com/h-lame/parental_control
http://railscasts.com/episodes/75-complex-forms-part-3
Advanced Rails Recipes, Pragmatic Programmer Series

Wolfram Arnold www.rubyfocus.biz
Thank you!

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2009 07 21: Nested Attributes

by Wolfram Arnold

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