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.

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 382
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] # => Fixnum

# File activerecord/lib/active_record/attribute_methods.rb, line 396
def []=(attr_name, value)
  write_attribute(attr_name, value)
end

Returns an #inspect-like string for the value of the attribute attr_name. String attributes are truncated upto 50 characters, Date and Time attributes are returned in the :db format, Array attributes are truncated upto 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 313
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

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 273
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

person = Task.new(title: '', is_done: false)
person.attribute_present?(:title)   # => false
person.attribute_present?(:is_done) # => true
person.name = 'Francesco'
person.is_done = true
person.attribute_present?(:title)   # => true
person.attribute_present?(:is_done) # => true

# File activerecord/lib/active_record/attribute_methods.rb, line 343
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 activerecord/lib/active_record/attribute_methods.rb, line 285
def attributes
  attribute_names.each_with_object({}) { |name, attrs|
    attrs[name] = read_attribute(name)
  }
end

Returns the column object for the named attribute. Returns nil if the named attribute not exists.

class Person < ActiveRecord::Base
end

person = Person.new
person.column_for_attribute(:name) # the result depends on the ConnectionAdapter
# => #<ActiveRecord::ConnectionAdapters::SQLite3Column:0x007ff4ab083980 @name="name", @sql_type="varchar(255)", @null=true, ...>

person.column_for_attribute(:nothing)
# => nil

# File activerecord/lib/active_record/attribute_methods.rb, line 360
def column_for_attribute(name)
  # FIXME: should this return a null object for columns that don't exist?
  self.class.columns_hash[name.to_s]
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 activerecord/lib/active_record/attribute_methods.rb, line 261
def has_attribute?(attr_name)
  @attributes.has_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 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 233
def respond_to?(name, include_private = false)
  name = name.to_s
  self.class.define_attribute_methods
  result = super

  # If the result is false the answer is false.
  return false unless result

  # 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) && @attributes.any? && self.class.column_names.include?(name)
    return has_attribute?(name)
  end

  return true
end