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Active Record Attribute Methods

Namespace
Methods
#
A
H
R
Included Modules
Constants
AttrNames = Module.new { def self.set_name_cache(name, value) const_name = "ATTR_#{name}" unless const_defined? const_name const_set const_name, value.dup.freeze end end }
 
BLACKLISTED_CLASS_METHODS = %w(private public protected)
 
Instance Public methods
[](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.

Alias for the read_attribute method.

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 activerecord/lib/active_record/attribute_methods.rb, line 355
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] # => Fixnum
# File activerecord/lib/active_record/attribute_methods.rb, line 369
def []=(attr_name, value)
  write_attribute(attr_name, value)
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, Array attributes are truncated up to 10 values. 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, ...]"
# File activerecord/lib/active_record/attribute_methods.rb, line 301
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)
    %Q("#{value.to_s(:db)}")
  elsif value.is_a?(Array) && value.size > 10
    inspected = value.first(10).inspect
    %Q(#{inspected[0...-1]}, ...])
  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"]
# File activerecord/lib/active_record/attribute_methods.rb, line 268
def attribute_names
  @attributes.keys
end
attribute_present?(attribute)

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 activerecord/lib/active_record/attribute_methods.rb, line 331
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}
# File activerecord/lib/active_record/attribute_methods.rb, line 280
def attributes
  @attributes.to_hash
end
has_attribute?(attr_name)

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 activerecord/lib/active_record/attribute_methods.rb, line 256
def has_attribute?(attr_name)
  @attributes.key?(attr_name.to_s)
end
respond_to?(name, include_private = false)

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 define 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 activerecord/lib/active_record/attribute_methods.rb, line 232
def respond_to?(name, include_private = false)
  return false unless super
  name = name.to_s

  # 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

  return true
end