module ActiveRecord::AttributeMethods::ClassMethods

def _has_attribute?(attr_name) # :nodoc:

:nodoc: 
def _has_attribute?(attr_name) # :nodoc:
  attribute_types.key?(attr_name)
end

def alias_attribute(new_name, old_name)

# SELECT "people".* FROM "people" WHERE "people"."name" = "Bob"
Person.where(nickname: "Bob")

The alias can also be used for querying:

person.nickname # => "Bob"
person.name # => "Bob"
person = Person.create(name: 'Bob')

end
alias_attribute :nickname, :name
class Person < ActiveRecord::Base

Allows you to make aliases for attributes. 
def alias_attribute(new_name, old_name)
  super
  if @alias_attributes_mass_generated
    ActiveSupport::CodeGenerator.batch(generated_attribute_methods, __FILE__, __LINE__) do |code_generator|
      generate_alias_attribute_methods(code_generator, new_name, old_name)
    end
  end
end

def alias_attribute_method_definition(code_generator, pattern, new_name, old_name) # :nodoc:

:nodoc: 
def alias_attribute_method_definition(code_generator, pattern, new_name, old_name) # :nodoc:
  old_name = old_name.to_s
  if !abstract_class? && !has_attribute?(old_name)
    raise ArgumentError, "#{self.name} model aliases `#{old_name}`, but `#{old_name}` is not an attribute. " \
      "Use `alias_method :#{new_name}, :#{old_name}` or define the method manually."
  else
    define_attribute_method_pattern(pattern, old_name, owner: code_generator, as: new_name, override: true)
  end
end

def attribute_method?(attribute)

Person.attribute_method?(:nothing) # => false
Person.attribute_method?(:age=) # => true
Person.attribute_method?('name') # => true

end
class Person < ActiveRecord::Base

+false+ otherwise.
Returns +true+ if +attribute+ is an attribute method and table exists, 
def attribute_method?(attribute)
  super || (table_exists? && column_names.include?(attribute.to_s.delete_suffix("=")))
end

def attribute_methods_generated? # :nodoc:

:nodoc: 
def attribute_methods_generated? # :nodoc:
  @attribute_methods_generated
end

def attribute_names

# => ["id", "created_at", "updated_at", "name", "age"]
Person.attribute_names

end
class Person < ActiveRecord::Base

table exists. Otherwise it returns an empty array.
Returns an array of column names as strings if it's not an abstract class and 
def attribute_names
  @attribute_names ||= if !abstract_class? && table_exists?
    attribute_types.keys
  else
    []
  end.freeze
end

def dangerous_attribute_method?(name) # :nodoc:

:nodoc:
not by any ancestors. (So 'puts' is not dangerous but 'save' is.)
A method name is 'dangerous' if it is already (re)defined by Active Record, but 
def dangerous_attribute_method?(name) # :nodoc:
  ::ActiveRecord::AttributeMethods.dangerous_attribute_methods.include?(name.to_s)
end

def dangerous_class_method?(method_name)

not by any ancestors. (So 'puts' is not dangerous but 'new' is.)
A class method is 'dangerous' if it is already (re)defined by Active Record, but 
def dangerous_class_method?(method_name)
  return true if RESTRICTED_CLASS_METHODS.include?(method_name.to_s)
  if Base.respond_to?(method_name, true)
    if Object.respond_to?(method_name, true)
      Base.method(method_name).owner != Object.method(method_name).owner
    else
      true
    end
  else
    false
  end
end

def define_attribute_methods # :nodoc:

:nodoc:
accessors, mutators and query methods.
Generates all the attribute related methods for columns in the database 
def define_attribute_methods # :nodoc:
  return false if @attribute_methods_generated
  # Use a mutex; we don't want two threads simultaneously trying to define
  # attribute methods.
  GeneratedAttributeMethods::LOCK.synchronize do
    return false if @attribute_methods_generated
    superclass.define_attribute_methods unless base_class?
    unless abstract_class?
      load_schema
      super(attribute_names)
      alias_attribute :id_value, :id if _has_attribute?("id")
    end
    generate_alias_attributes
    @attribute_methods_generated = true
  end
  true
end

def eagerly_generate_alias_attribute_methods(_new_name, _old_name) # :nodoc:

:nodoc: 
def eagerly_generate_alias_attribute_methods(_new_name, _old_name) # :nodoc:
  # alias attributes in Active Record are lazily generated
end

def generate_alias_attribute_methods(code_generator, new_name, old_name) # :nodoc:

:nodoc: 
def generate_alias_attribute_methods(code_generator, new_name, old_name) # :nodoc:
  attribute_method_patterns.each do |pattern|
    alias_attribute_method_definition(code_generator, pattern, new_name, old_name)
  end
  attribute_method_patterns_cache.clear
end

def generate_alias_attributes # :nodoc:

:nodoc: 
def generate_alias_attributes # :nodoc:
  superclass.generate_alias_attributes unless superclass == Base
  return if @alias_attributes_mass_generated
  ActiveSupport::CodeGenerator.batch(generated_attribute_methods, __FILE__, __LINE__) do |code_generator|
    aliases_by_attribute_name.each do |old_name, new_names|
      new_names.each do |new_name|
        generate_alias_attribute_methods(code_generator, new_name, old_name)
      end
    end
  end
  @alias_attributes_mass_generated = true
end

def has_attribute?(attr_name)

Person.has_attribute?(:nothing) # => false
Person.has_attribute?(:age) # => true
Person.has_attribute?('new_name') # => true
Person.has_attribute?('name') # => true

end
alias_attribute :new_name, :name
class Person < ActiveRecord::Base

Returns true if the given attribute exists, otherwise false. 
def has_attribute?(attr_name)
  attr_name = attr_name.to_s
  attr_name = attribute_aliases[attr_name] || attr_name
  attribute_types.key?(attr_name)
end

def inherited(child_class) 

def inherited(child_class)
  super
  child_class.initialize_generated_modules
  child_class.class_eval do
    @alias_attributes_mass_generated = false
    @attribute_names = nil
  end
end

def initialize_generated_modules # :nodoc:

:nodoc: 
def initialize_generated_modules # :nodoc:
  @generated_attribute_methods = const_set(:GeneratedAttributeMethods, GeneratedAttributeMethods.new)
  private_constant :GeneratedAttributeMethods
  @attribute_methods_generated = false
  @alias_attributes_mass_generated = false
  include @generated_attribute_methods
  super
end

def instance_method_already_implemented?(method_name)

# => false
Person.instance_method_already_implemented?(:name)

# => ActiveRecord::DangerousAttributeError: save is defined by Active Record. Check to make sure that you don't have an attribute or method with the same name.
Person.instance_method_already_implemented?(:save)

end
end
'already defined by Active Record'
def save
class Person < ActiveRecord::Base

\Active \Record method is defined in the model, otherwise +false+.
Raises an ActiveRecord::DangerousAttributeError exception when an 
def instance_method_already_implemented?(method_name)
  if dangerous_attribute_method?(method_name)
    raise DangerousAttributeError, "#{method_name} is defined by Active Record. Check to make sure that you don't have an attribute or method with the same name."
  end
  if superclass == Base
    super
  else
    # If ThisClass < ... < SomeSuperClass < ... < Base and SomeSuperClass
    # defines its own attribute method, then we don't want to override that.
    defined = method_defined_within?(method_name, superclass, Base) &&
      ! superclass.instance_method(method_name).owner.is_a?(GeneratedAttributeMethods)
    defined || super
  end
end

def method_defined_within?(name, klass, superklass = klass.superclass) # :nodoc:

:nodoc: 
def method_defined_within?(name, klass, superklass = klass.superclass) # :nodoc:
  if klass.method_defined?(name) || klass.private_method_defined?(name)
    if superklass.method_defined?(name) || superklass.private_method_defined?(name)
      klass.instance_method(name).owner != superklass.instance_method(name).owner
    else
      true
    end
  else
    false
  end
end

def undefine_attribute_methods # :nodoc:

:nodoc: 
def undefine_attribute_methods # :nodoc:
  GeneratedAttributeMethods::LOCK.synchronize do
    super if @attribute_methods_generated
    @attribute_methods_generated = false
    @alias_attributes_mass_generated = false
  end
end