module ActiveRecord::AttributeMethods

Active Record Attribute Methods

Constants

RESTRICTED_CLASS_METHODS

Public Instance Methods

[](attr_name) click to toggle source

Returns the value of the attribute identified by attr_name after it has been typecast (for example, “2004-12-12” in a date column is cast to a date object, like Date.new(2004, 12, 12)). It raises ActiveModel::MissingAttributeError if the identified attribute is missing.

Note: :id is always present.

class Person < ActiveRecord::Base
  belongs_to :organization
end

person = Person.new(name: 'Francesco', age: '22')
person[:name] # => "Francesco"
person[:age]  # => 22

person = Person.select('id').first
person[:name]            # => ActiveModel::MissingAttributeError: missing attribute: name
person[:organization_id] # => ActiveModel::MissingAttributeError: missing attribute: organization_id
# File lib/active_record/attribute_methods.rb, line 321
def [](attr_name)
  read_attribute(attr_name) { |n| missing_attribute(n, caller) }
end
[]=(attr_name, value) click to toggle source

Updates the attribute identified by attr_name with the specified value. (Alias for the protected write_attribute method).

class Person < ActiveRecord::Base
end

person = Person.new
person[:age] = '22'
person[:age] # => 22
person[:age].class # => Integer
# File lib/active_record/attribute_methods.rb, line 335
def []=(attr_name, value)
  write_attribute(attr_name, value)
end
accessed_fields() click to toggle source

Returns the name of all database fields which have been read from this model. This can be useful in development mode to determine which fields need to be selected. For performance critical pages, selecting only the required fields can be an easy performance win (assuming you aren't using all of the fields on the model).

For example:

class PostsController < ActionController::Base
  after_action :print_accessed_fields, only: :index

  def index
    @posts = Post.all
  end

  private

  def print_accessed_fields
    p @posts.first.accessed_fields
  end
end

Which allows you to quickly change your code to:

class PostsController < ActionController::Base
  def index
    @posts = Post.select(:id, :title, :author_id, :updated_at)
  end
end
# File lib/active_record/attribute_methods.rb, line 368
def accessed_fields
  @attributes.accessed
end
attribute_for_inspect(attr_name) click to toggle source

Returns an #inspect-like string for the value of the attribute attr_name. String attributes are truncated up to 50 characters, Date and Time attributes are returned in the :db format. Other attributes return the value of #inspect without modification.

person = Person.create!(name: 'David Heinemeier Hansson ' * 3)

person.attribute_for_inspect(:name)
# => "\"David Heinemeier Hansson David Heinemeier Hansson ...\""

person.attribute_for_inspect(:created_at)
# => "\"2012-10-22 00:15:07\""

person.attribute_for_inspect(:tag_ids)
# => "[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]"
# File lib/active_record/attribute_methods.rb, line 279
def attribute_for_inspect(attr_name)
  value = _read_attribute(attr_name)
  format_for_inspect(value)
end
attribute_names() click to toggle source

Returns an array of names for the attributes available on this object.

class Person < ActiveRecord::Base
end

person = Person.new
person.attribute_names
# => ["id", "created_at", "updated_at", "name", "age"]
# File lib/active_record/attribute_methods.rb, line 247
def attribute_names
  @attributes.keys
end
attribute_present?(attribute) click to toggle source

Returns true if the specified attribute has been set by the user or by a database load and is neither nil nor empty? (the latter only applies to objects that respond to empty?, most notably Strings). Otherwise, false. Note that it always returns true with boolean attributes.

class Task < ActiveRecord::Base
end

task = Task.new(title: '', is_done: false)
task.attribute_present?(:title)   # => false
task.attribute_present?(:is_done) # => true
task.title = 'Buy milk'
task.is_done = true
task.attribute_present?(:title)   # => true
task.attribute_present?(:is_done) # => true
# File lib/active_record/attribute_methods.rb, line 299
def attribute_present?(attribute)
  value = _read_attribute(attribute)
  !value.nil? && !(value.respond_to?(:empty?) && value.empty?)
end
attributes() click to toggle source

Returns a hash of all the attributes with their names as keys and the values of the attributes as values.

class Person < ActiveRecord::Base
end

person = Person.create(name: 'Francesco', age: 22)
person.attributes
# => {"id"=>3, "created_at"=>Sun, 21 Oct 2012 04:53:04, "updated_at"=>Sun, 21 Oct 2012 04:53:04, "name"=>"Francesco", "age"=>22}
# File lib/active_record/attribute_methods.rb, line 259
def attributes
  @attributes.to_hash
end
has_attribute?(attr_name) click to toggle source

Returns true if the given attribute is in the attributes hash, otherwise false.

class Person < ActiveRecord::Base
end

person = Person.new
person.has_attribute?(:name)    # => true
person.has_attribute?('age')    # => true
person.has_attribute?(:nothing) # => false
# File lib/active_record/attribute_methods.rb, line 235
def has_attribute?(attr_name)
  @attributes.key?(attr_name.to_s)
end
respond_to?(name, include_private = false) click to toggle source

A Person object with a name attribute can ask person.respond_to?(:name), person.respond_to?(:name=), and person.respond_to?(:name?) which will all return true. It also defines the attribute methods if they have not been generated.

class Person < ActiveRecord::Base
end

person = Person.new
person.respond_to?(:name)    # => true
person.respond_to?(:name=)   # => true
person.respond_to?(:name?)   # => true
person.respond_to?('age')    # => true
person.respond_to?('age=')   # => true
person.respond_to?('age?')   # => true
person.respond_to?(:nothing) # => false
Calls superclass method
# File lib/active_record/attribute_methods.rb, line 210
def respond_to?(name, include_private = false)
  return false unless super

  # If the result is true then check for the select case.
  # For queries selecting a subset of columns, return false for unselected columns.
  # We check defined?(@attributes) not to issue warnings if called on objects that
  # have been allocated but not yet initialized.
  if defined?(@attributes)
    if name = self.class.symbol_column_to_string(name.to_sym)
      return has_attribute?(name)
    end
  end

  true
end

Private Instance Methods

attribute_method?(attr_name) click to toggle source
# File lib/active_record/attribute_methods.rb, line 373
def attribute_method?(attr_name)
  # We check defined? because Syck calls respond_to? before actually calling initialize.
  defined?(@attributes) && @attributes.key?(attr_name)
end
attributes_for_create(attribute_names) click to toggle source

Filters out the primary keys, from the attribute names, when the primary key is to be generated (e.g. the id attribute has no value).

# File lib/active_record/attribute_methods.rb, line 394
def attributes_for_create(attribute_names)
  attribute_names &= self.class.column_names
  attribute_names.delete_if do |name|
    pk_attribute?(name) && id.nil?
  end
end
attributes_for_update(attribute_names) click to toggle source

Filters the primary keys and readonly attributes from the attribute names.

# File lib/active_record/attribute_methods.rb, line 385
def attributes_for_update(attribute_names)
  attribute_names &= self.class.column_names
  attribute_names.delete_if do |name|
    readonly_attribute?(name)
  end
end
attributes_with_values(attribute_names) click to toggle source
# File lib/active_record/attribute_methods.rb, line 378
def attributes_with_values(attribute_names)
  attribute_names.each_with_object({}) do |name, attrs|
    attrs[name] = _read_attribute(name)
  end
end
format_for_inspect(value) click to toggle source
# File lib/active_record/attribute_methods.rb, line 401
def format_for_inspect(value)
  if value.is_a?(String) && value.length > 50
    "#{value[0, 50]}...".inspect
  elsif value.is_a?(Date) || value.is_a?(Time)
    %("#{value.to_s(:db)}")
  else
    value.inspect
  end
end
pk_attribute?(name) click to toggle source
# File lib/active_record/attribute_methods.rb, line 415
def pk_attribute?(name)
  name == @primary_key
end
readonly_attribute?(name) click to toggle source
# File lib/active_record/attribute_methods.rb, line 411
def readonly_attribute?(name)
  self.class.readonly_attributes.include?(name)
end