module Devise::Models

def self.config(mod, *accessors) #:nodoc:

:nodoc:

inside the given class.
To add the class methods you need to have a module ClassMethods defined

3) And an instance method stretches.

which have higher priority than Devise.stretches;
2) Some class methods for your model Model.stretches and Model.stretches=

1) An accessor called Devise.stretches, which value is used by default;

The line above creates:

Devise::Models.config(Devise::Authenticable, :stretches, 10)

Creates configuration values for Devise and for the given module.

def self.config(mod, *accessors) #:nodoc:
  accessors.each do |accessor|
    mod.class_eval <<-METHOD, __FILE__, __LINE__ + 1
      def #{accessor}
        if defined?(@#{accessor})
          @#{accessor}
        elsif superclass.respond_to?(:#{accessor})
          superclass.#{accessor}
        else
          Devise.#{accessor}
        end
      end
      def #{accessor}=(value)
        @#{accessor} = value
      end
    METHOD
  end
end

def add_error_on(record, attribute, error, add_default=true)

Wraps add error logic in a method that works for different frameworks.

def add_error_on(record, attribute, error, add_default=true)
  options = add_default ? { :default => error.to_s.gsub("_", " ") } : {}
  begin
    record.errors.add(attribute, error, options)
  rescue ArgumentError
    record.errors.add(attribute, error.to_s.gsub("_", " "))
  end
end

def devise(*modules)

for a complete description on those values.
with specific values for this model. Please check your Devise initializer
You can also give any of the devise configuration values in form of a hash,

devise :authenticatable, :confirmable, :recoverable

Include the chosen devise modules in your model:

def devise(*modules)
  raise "You need to give at least one Devise module" if modules.empty?
  options = modules.extract_options!
  if modules.delete(:authenticatable)
    ActiveSupport::Deprecation.warn ":authenticatable as module is deprecated. Please give :database_authenticatable instead.", caller
    modules << :database_authenticatable
  end
  @devise_modules = Devise::ALL & modules.map(&:to_sym).uniq
  Devise.orm_class.included_modules_hook(self) do
    devise_modules.each do |m|
      include Devise::Models.const_get(m.to_s.classify)
    end
    options.each { |key, value| send(:"#{key}=", value) }
  end
end

def devise_modules

which routes are needed.
Stores all modules included inside the model, so we are able to verify

def devise_modules
  @devise_modules ||= []
end

def find_or_initialize_with_error_by(attribute, value, error=:invalid)

Find an initialize a record setting an error if it can't be found.

def find_or_initialize_with_error_by(attribute, value, error=:invalid)
  if value.present?
    conditions = { attribute => value }
    record = find(:first, :conditions => conditions)
  end
  unless record
    record = new
    if value.present?
      record.send(:"#{attribute}=", value)
    else
      error, skip_default = :blank, true
    end
    add_error_on(record, attribute, error, !skip_default)
  end
  record
end

Modules

Classes