module ActiveRecord::AttributeMethods
Active Record Attribute Methods¶ ↑
Constants
- AttrNames
- BLACKLISTED_CLASS_METHODS
Public Instance Methods
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 395 def [](attr_name) read_attribute(attr_name) { |n| missing_attribute(n, caller) } end
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 409 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 442 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, 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 346 def attribute_for_inspect(attr_name) value = read_attribute(attr_name) 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
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 314 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 373 def attribute_present?(attribute) value = _read_attribute(attribute) !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 326 def attributes @attributes.to_hash end
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 302 def has_attribute?(attr_name) @attributes.key?(attr_name.to_s) 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 270 def respond_to?(name, include_private = false) return false unless super case name when :to_partial_path name = "to_partial_path".freeze when :to_model name = "to_model".freeze else name = name.to_s end # 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) && self.class.column_names.include?(name) return has_attribute?(name) end true end
Private Instance Methods
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 478 def attributes_for_create(attribute_names) attribute_names.reject do |name| pk_attribute?(name) && id.nil? end end
Filters the primary keys and readonly attributes from the attribute names.
# File lib/active_record/attribute_methods.rb, line 470 def attributes_for_update(attribute_names) attribute_names.reject do |name| readonly_attribute?(name) end end
# File lib/active_record/attribute_methods.rb, line 463 def attributes_with_values(attribute_names) attribute_names.each_with_object({}) do |name, attrs| attrs[name] = _read_attribute(name) end end
# File lib/active_record/attribute_methods.rb, line 455 def attributes_with_values_for_create(attribute_names) attributes_with_values(attributes_for_create(attribute_names)) end
# File lib/active_record/attribute_methods.rb, line 459 def attributes_with_values_for_update(attribute_names) attributes_with_values(attributes_for_update(attribute_names)) end
# File lib/active_record/attribute_methods.rb, line 488 def pk_attribute?(name) name == self.class.primary_key end
# File lib/active_record/attribute_methods.rb, line 484 def readonly_attribute?(name) self.class.readonly_attributes.include?(name) end