rails--rails/activemodel/CHANGELOG.md

• Assigning an unknown attribute key to an ActiveModel instance during initialization will now raise ActiveModel::AttributeAssignment::UnknownAttributeError instead of NoMethodError

  Example:

  User.new(foo: 'some value')
  # => ActiveModel::AttributeAssignment::UnknownAttributeError: unknown attribute 'foo' for User.
  

  Eugene Gilburg

• Extracted ActiveRecord::AttributeAssignment to ActiveModel::AttributeAssignment allowing to use it for any object as an includable module.

  Example:

  class Cat
    include ActiveModel::AttributeAssignment
    attr_accessor :name, :status
  end
  
  cat = Cat.new
  cat.assign_attributes(name: "Gorby", status: "yawning")
  cat.name # => 'Gorby'
  cat.status => 'yawning'
  cat.assign_attributes(status: "sleeping")
  cat.name # => 'Gorby'
  cat.status => 'sleeping'
  

  Bogdan Gusiev

• Add ActiveModel::Errors#details

  To be able to return type of used validator, one can now call details on errors instance.

  Example:

  class User < ActiveRecord::Base
    validates :name, presence: true
  end
  
  user = User.new; user.valid?; user.errors.details
  => {name: [{error: :blank}]}
  

  Wojciech Wnętrzak

• Change validates_acceptance_of to accept true by default.

  The default for validates_acceptance_of is now "1" and true. In the past, only "1" was the default and you were required to add accept: true.

• Remove deprecated ActiveModel::Dirty#reset_#{attribute} and ActiveModel::Dirty#reset_changes.

  Rafael Mendonça França

• Change the way in which callback chains can be halted.

  The preferred method to halt a callback chain from now on is to explicitly throw(:abort). In the past, returning false in an ActiveModel or ActiveModel::Validations before_ callback had the side effect of halting the callback chain. This is not recommended anymore and, depending on the value of the config.active_support.halt_callback_chains_on_return_false option, will either not work at all or display a deprecation warning.

Please check 4-2-stable for previous changes.