Reflection allows you to interrogate Active Record classes and objects about their associations and aggregations. This information can, for example, be used in a form builder that took an Active Record object and created input fields for all of the attributes depending on their type and displayed the associations to other objects.

You can find the interface for the AggregateReflection and AssociationReflection classes in the abstract MacroReflection class.

Public Instance methods
create_reflection(macro, name, options, active_record)
    # File activerecord/lib/active_record/reflection.rb, line 13
13:       def create_reflection(macro, name, options, active_record)
14:         case macro
15:           when :has_many, :belongs_to, :has_one, :has_and_belongs_to_many
16:             klass = options[:through] ? ThroughReflection : AssociationReflection
17:             reflection =, name, options, active_record)
18:           when :composed_of
19:             reflection =, name, options, active_record)
20:         end
21:         write_inheritable_hash :reflections, name => reflection
22:         reflection
23:       end

Returns the AggregateReflection object for the named aggregation (use the symbol). Example:

  Account.reflect_on_aggregation(:balance) # returns the balance AggregateReflection
    # File activerecord/lib/active_record/reflection.rb, line 44
44:       def reflect_on_aggregation(aggregation)
45:         reflections[aggregation].is_a?(AggregateReflection) ? reflections[aggregation] : nil
46:       end

Returns an array of AggregateReflection objects for all the aggregations in the class.

    # File activerecord/lib/active_record/reflection.rb, line 36
36:       def reflect_on_all_aggregations
37: { |reflection| reflection.is_a?(AggregateReflection) }
38:       end
reflect_on_all_associations(macro = nil)

Returns an array of AssociationReflection objects for all the associations in the class. If you only want to reflect on a certain association type, pass in the symbol (:has_many, :has_one, :belongs_to) for that as the first parameter. Example:

  Account.reflect_on_all_associations             # returns an array of all associations
  Account.reflect_on_all_associations(:has_many)  # returns an array of all has_many associations
    # File activerecord/lib/active_record/reflection.rb, line 55
55:       def reflect_on_all_associations(macro = nil)
56:         association_reflections = { |reflection| reflection.is_a?(AssociationReflection) }
57:         macro ? { |reflection| reflection.macro == macro } : association_reflections
58:       end

Returns an array of AssociationReflection objects for all associations which have :autosave enabled.

    # File activerecord/lib/active_record/reflection.rb, line 70
70:       def reflect_on_all_autosave_associations
71: { |reflection| reflection.options[:autosave] }
72:       end

Returns the AssociationReflection object for the named association (use the symbol). Example:

  Account.reflect_on_association(:owner) # returns the owner AssociationReflection
  Invoice.reflect_on_association(:line_items).macro  # returns :has_many
    # File activerecord/lib/active_record/reflection.rb, line 65
65:       def reflect_on_association(association)
66:         reflections[association].is_a?(AssociationReflection) ? reflections[association] : nil
67:       end

Returns a hash containing all AssociationReflection objects for the current class Example:

    # File activerecord/lib/active_record/reflection.rb, line 31
31:       def reflections
32:         read_inheritable_attribute(:reflections) || write_inheritable_attribute(:reflections, {})
33:       end