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Module: ActiveRecord::AttributeMethods

Constant Summary

::ActiveModel::AttributeMethods - Included

CALL_COMPILABLE_REGEXP, NAME_COMPILABLE_REGEXP

::ActiveModel::AttributeMethods - Attributes & Methods

Class Method Summary

Instance Method Summary

  • #[](attr_name)

    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)).

  • #[]=(attr_name, value)

    Updates the attribute identified by attr_name with the specified value.

  • #accessed_fields

    Returns the name of all database fields which have been read from this model.

  • #attribute_for_inspect(attr_name)

    Returns an #inspect-like string for the value of the attribute attr_name.

  • #attribute_names

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

  • #attribute_present?(attribute) ⇒ Boolean

    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).

  • #attributes

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

  • #has_attribute?(attr_name) ⇒ Boolean

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

  • #respond_to?(name, include_private = false) ⇒ Boolean

    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.

::ActiveModel::AttributeMethods - Included

#attribute_missing

attribute_missing is like method_missing, but for attributes.

#method_missing

Allows access to the object attributes, which are held in the hash returned by #attributes, as though they were first-class methods.

#respond_to?,
#respond_to_without_attributes?

A Person instance with a name attribute can ask person.respond_to?(:name), person.respond_to?(:name=), and person.respond_to?(:name?) which will all return true.

Dynamic Method Handling

This class handles dynamic methods through the method_missing method in the class ActiveModel::AttributeMethods

DSL Calls

included

[ GitHub ]


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# File 'activerecord/lib/active_record/attribute_methods.rb', line 11

included do
  initialize_generated_modules
  include Read
  include Write
  include BeforeTypeCast
  include Query
  include PrimaryKey
  include TimeZoneConversion
  include Dirty
  include Serialization

  delegate :column_for_attribute, to: :class
end

Class Attribute Details

.attribute_aliases (rw)

[ GitHub ]

  
# File 'activemodel/lib/active_model/attribute_methods.rb', line 72

class_attribute :attribute_aliases, instance_writer: false, default: {}

.attribute_aliases?Boolean (rw)

[ GitHub ]

  
# File 'activemodel/lib/active_model/attribute_methods.rb', line 72

class_attribute :attribute_aliases, instance_writer: false, default: {}

.attribute_method_matchers (rw)

[ GitHub ]

  
# File 'activemodel/lib/active_model/attribute_methods.rb', line 73

class_attribute :attribute_method_matchers, instance_writer: false, default: [ ClassMethods::AttributeMethodMatcher.new ]

.attribute_method_matchers?Boolean (rw)

[ GitHub ]

  
# File 'activemodel/lib/active_model/attribute_methods.rb', line 73

class_attribute :attribute_method_matchers, instance_writer: false, default: [ ClassMethods::AttributeMethodMatcher.new ]

Instance Attribute Details

#attribute_aliases (readonly)

[ GitHub ]

  
# File 'activemodel/lib/active_model/attribute_methods.rb', line 72

class_attribute :attribute_aliases, instance_writer: false, default: {}

#attribute_aliases?Boolean (readonly)

[ GitHub ]

  
# File 'activemodel/lib/active_model/attribute_methods.rb', line 72

class_attribute :attribute_aliases, instance_writer: false, default: {}

#attribute_method_matchers (readonly)

[ GitHub ]

  
# File 'activemodel/lib/active_model/attribute_methods.rb', line 73

class_attribute :attribute_method_matchers, instance_writer: false, default: [ ClassMethods::AttributeMethodMatcher.new ]

#attribute_method_matchers?Boolean (readonly)

[ GitHub ]

  
# File 'activemodel/lib/active_model/attribute_methods.rb', line 73

class_attribute :attribute_method_matchers, instance_writer: false, default: [ ClassMethods::AttributeMethodMatcher.new ]

Instance Method Details

#[](attr_name)

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
[ GitHub ]

  
# File 'activerecord/lib/active_record/attribute_methods.rb', line 395

def [](attr_name)
  read_attribute(attr_name) { |n| missing_attribute(n, caller) }
end

#[]=(attr_name, value)

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
[ GitHub ]

  
# File 'activerecord/lib/active_record/attribute_methods.rb', line 409

def []=(attr_name, value)
  write_attribute(attr_name, value)
end

#accessed_fields

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
[ GitHub ]

  
# File 'activerecord/lib/active_record/attribute_methods.rb', line 442

def accessed_fields
  @attributes.accessed
end

#attribute_for_inspect(attr_name)

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]"
[ GitHub ]

  
# File 'activerecord/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

#attribute_names

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"]
[ GitHub ]

  
# File 'activerecord/lib/active_record/attribute_methods.rb', line 314

def attribute_names
  @attributes.keys
end

#attribute_present?(attribute) ⇒ Boolean

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
[ GitHub ]

  
# File 'activerecord/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

#attributes

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}
[ GitHub ]

  
# File 'activerecord/lib/active_record/attribute_methods.rb', line 326

def attributes
  @attributes.to_hash
end

#has_attribute?(attr_name) ⇒ Boolean

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
[ GitHub ]

  
# File 'activerecord/lib/active_record/attribute_methods.rb', line 302

def has_attribute?(attr_name)
  @attributes.key?(attr_name.to_s)
end

#respond_to?(name, include_private = false) ⇒ Boolean

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
[ GitHub ]

  
# File 'activerecord/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