module ActiveRecord::AttributeMethods
Active Record Attribute Methods¶ ↑
Constants
- RESTRICTED_CLASS_METHODS
Public Instance Methods
Returns the value of the attribute identified by attr_name
after it has been type cast. (For information about specific type casting behavior, see the types under ActiveModel::Type.)
class Person < ActiveRecord::Base belongs_to :organization end person = Person.new(name: "Francesco", date_of_birth: "2004-12-12") person[:name] # => "Francesco" person[:date_of_birth] # => Date.new(2004, 12, 12) person[:organization_id] # => nil
Raises ActiveModel::MissingAttributeError if the attribute is missing. Note, however, that the id
attribute will never be considered missing.
person = Person.select(:name).first person[:name] # => "Francesco" person[:date_of_birth] # => ActiveModel::MissingAttributeError: missing attribute 'date_of_birth' for Person person[:organization_id] # => ActiveModel::MissingAttributeError: missing attribute 'organization_id' for Person person[:id] # => nil
# File lib/active_record/attribute_methods.rb, line 414 def [](attr_name) read_attribute(attr_name) { |n| missing_attribute(n, caller) } end
Updates the attribute identified by attr_name
using the specified value
. The attribute value will be type cast upon being read.
class Person < ActiveRecord::Base end person = Person.new person[:date_of_birth] = "2004-12-12" person[:date_of_birth] # => Date.new(2004, 12, 12)
# File lib/active_record/attribute_methods.rb, line 427 def []=(attr_name, value) write_attribute(attr_name, value) end
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 459 def accessed_fields @attributes.accessed end
Returns an #inspect
-like string for the value of the attribute attr_name
. String attributes are truncated up to 50 characters. 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 00:15:07.000000000 +0000\"" 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 364 def attribute_for_inspect(attr_name) attr_name = attr_name.to_s attr_name = self.class.attribute_aliases[attr_name] || attr_name value = _read_attribute(attr_name) format_for_inspect(attr_name, value) end
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 333 def attribute_names @attributes.keys end
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 386 def attribute_present?(attr_name) attr_name = attr_name.to_s attr_name = self.class.attribute_aliases[attr_name] || attr_name value = _read_attribute(attr_name) !value.nil? && !(value.respond_to?(:empty?) && value.empty?) end
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 345 def attributes @attributes.to_hash end
Returns true
if the given attribute is in the attributes hash, otherwise false
.
class Person < ActiveRecord::Base alias_attribute :new_name, :name end person = Person.new person.has_attribute?(:name) # => true person.has_attribute?(:new_name) # => true person.has_attribute?('age') # => true person.has_attribute?(:nothing) # => false
# File lib/active_record/attribute_methods.rb, line 315 def has_attribute?(attr_name) attr_name = attr_name.to_s attr_name = self.class.attribute_aliases[attr_name] || attr_name @attributes.key?(attr_name) end
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
# File lib/active_record/attribute_methods.rb, line 290 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. if @attributes if name = self.class.symbol_column_to_string(name.to_sym) return _has_attribute?(name) end end true end
Private Instance Methods
# File lib/active_record/attribute_methods.rb, line 494 def attribute_method?(attr_name) @attributes&.key?(attr_name) end
Filters out the virtual columns and also 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 514 def attributes_for_create(attribute_names) attribute_names &= self.class.column_names attribute_names.delete_if do |name| (pk_attribute?(name) && id.nil?) || column_for_attribute(name).virtual? end end
Filters the primary keys, readonly attributes and virtual columns from the attribute names.
# File lib/active_record/attribute_methods.rb, line 503 def attributes_for_update(attribute_names) attribute_names &= self.class.column_names attribute_names.delete_if do |name| self.class.readonly_attribute?(name) || self.class.counter_cache_column?(name) || column_for_attribute(name).virtual? end end
# File lib/active_record/attribute_methods.rb, line 498 def attributes_with_values(attribute_names) attribute_names.index_with { |name| @attributes[name] } end
# File lib/active_record/attribute_methods.rb, line 522 def format_for_inspect(name, value) if value.nil? value.inspect else inspected_value = if value.is_a?(String) && value.length > 50 "#{value[0, 50]}...".inspect elsif value.is_a?(Date) || value.is_a?(Time) %("#{value.to_fs(:inspect)}") else value.inspect end inspection_filter.filter_param(name, inspected_value) end end
# File lib/active_record/attribute_methods.rb, line 474 def method_missing(name, ...) unless self.class.attribute_methods_generated? if self.class.method_defined?(name) # The method is explicitly defined in the model, but calls a generated # method with super. So we must resume the call chain at the right step. last_method = method(name) last_method = last_method.super_method while last_method.super_method self.class.define_attribute_methods if last_method.super_method return last_method.super_method.call(...) end elsif self.class.define_attribute_methods # Some attribute methods weren't generated yet, we retry the call return public_send(name, ...) end end super end
# File lib/active_record/attribute_methods.rb, line 538 def pk_attribute?(name) name == @primary_key end
# File lib/active_record/attribute_methods.rb, line 464 def respond_to_missing?(name, include_private = false) if self.class.define_attribute_methods # Some methods weren't defined yet. return true if self.class.method_defined?(name) return true if include_private && self.class.private_method_defined?(name) end super end