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.
- create_reflection
- reflect_on_aggregation
- reflect_on_all_aggregations
- reflect_on_all_associations
- reflect_on_all_autosave_associations
- reflect_on_association
- reflections
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# 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 = klass.new(macro, name, options, active_record) 18: when :composed_of 19: reflection = AggregateReflection.new(macro, 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
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# 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.
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# File activerecord/lib/active_record/reflection.rb, line 36 36: def reflect_on_all_aggregations 37: reflections.values.select { |reflection| reflection.is_a?(AggregateReflection) } 38: end
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
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# File activerecord/lib/active_record/reflection.rb, line 55 55: def reflect_on_all_associations(macro = nil) 56: association_reflections = reflections.values.select { |reflection| reflection.is_a?(AssociationReflection) } 57: macro ? association_reflections.select { |reflection| reflection.macro == macro } : association_reflections 58: end
Returns an array of AssociationReflection objects for all associations which have :autosave enabled.
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# File activerecord/lib/active_record/reflection.rb, line 70 70: def reflect_on_all_autosave_associations 71: reflections.values.select { |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
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# 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:
Invoice.reflections Account.reflections
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# File activerecord/lib/active_record/reflection.rb, line 31 31: def reflections 32: read_inheritable_attribute(:reflections) || write_inheritable_attribute(:reflections, {}) 33: end