Rails Kitchen

It's a place to write on stuff I learned recently.

Rails 5 'Belongs_to' Associations Default to Required True

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5.0.0.beta2 version is released. One of the changes I noticed is belongs_to associations by default required is true, that means if you create an object by setting foreign key to be nil it will throw a must exist validation error. This change will have some impact if you are migrating an existing rails 4 application in to rails 5 and foreign key is not mandatory in your application.
For example, if your User model has city_id as forign key, then if you create user without adding city_id then rails 5 will throw validation error.
user.rb
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class User < ApplicationRecord
  belongs_to :city
end

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2.3.0 :003 > user = User.create(name:'Shaiju')
   (0.3ms)  BEGIN
   (0.2ms)  ROLLBACK
 => #<User id: nil, name: "Shaiju", city_id: nil, created_at: nil, updated_at: nil> 
2.3.0 :004 > user.errors
 => #<ActiveModel::Errors:0xa8d9a00 @base=#<User id: nil, name: "Shaiju", city_id: nil, created_at: nil, updated_at: nil>, @messages={:city=>["must exist"]}, @details={:city=>[{:error=>:blank}]}>
If we want to turn of this behavior we can use :optional => true . When set to true, the association will not have its presence validated.
user.rb
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class User < ApplicationRecord
  belongs_to :city,optional: true
end

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2.3.0 :001 > user = User.create(name:'Shaiju')
   (0.3ms)  BEGIN
  SQL (25.2ms)  INSERT INTO `users` (`name`, `created_at`, `updated_at`) VALUES ('Shaiju', '2016-02-15 12:25:55', '2016-02-15 12:25:55')
   (81.6ms)  COMMIT
 => #<User id: 1, name: "Shaiju", city_id: nil, created_at: "2016-02-15 12:25:55", updated_at: "2016-02-15 12:25:55">
You can turn off this in entire application by setting Rails.application. config.active_record.belongs_to_required_by_default = false in config/initializers/active_record_belongs_to_required_by_default.rb file.
config/initializers/active_record_belongs_to_required_by_default.rb 
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 # Be sure to restart your server when you modify this file.

# Require `belongs_to` associations by default. This is a new Rails 5.0
# default, so it is introduced as a configuration option to ensure that apps
# made on earlier versions of Rails are not affected when upgrading.
Rails.application.config.active_record.belongs_to_required_by_default = false

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