Reflection enables to interrogate Active Record classes and objects about their associations and aggregations. This information can, for example, be used in a form builder that takes an Active Record object and creates input fields for all of the attributes depending on their type and displays the associations to other objects.
MacroReflection class has info for AggregateReflection and AssociationReflection classes.
# File lib/active_record/reflection.rb, line 15 15: def create_reflection(macro, name, options, active_record) 16: case macro 17: when :has_many, :belongs_to, :has_one, :has_and_belongs_to_many 18: klass = options[:through] ? ThroughReflection : AssociationReflection 19: reflection = klass.new(macro, name, options, active_record) 20: when :composed_of 21: reflection = AggregateReflection.new(macro, name, options, active_record) 22: end 23: write_inheritable_hash :reflections, name => reflection 24: reflection 25: end
Returns the AggregateReflection object for the named aggregation (use the symbol).
Account.reflect_on_aggregation(:balance) # => the balance AggregateReflection
# File lib/active_record/reflection.rb, line 46 46: def reflect_on_aggregation(aggregation) 47: reflections[aggregation].is_a?(AggregateReflection) ? reflections[aggregation] : nil 48: end
Returns an array of AggregateReflection objects for all the aggregations in the class.
# File lib/active_record/reflection.rb, line 38 38: def reflect_on_all_aggregations 39: reflections.values.select { |reflection| reflection.is_a?(AggregateReflection) } 40: 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) 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 lib/active_record/reflection.rb, line 60 60: def reflect_on_all_associations(macro = nil) 61: association_reflections = reflections.values.select { |reflection| reflection.is_a?(AssociationReflection) } 62: macro ? association_reflections.select { |reflection| reflection.macro == macro } : association_reflections 63: end
Returns an array of AssociationReflection objects for all associations which have :autosave enabled.
# File lib/active_record/reflection.rb, line 75 75: def reflect_on_all_autosave_associations 76: reflections.values.select { |reflection| reflection.options[:autosave] } 77: end
Returns the AssociationReflection object for the association (use the symbol).
Account.reflect_on_association(:owner) # returns the owner AssociationReflection Invoice.reflect_on_association(:line_items).macro # returns :has_many
# File lib/active_record/reflection.rb, line 70 70: def reflect_on_association(association) 71: reflections[association].is_a?(AssociationReflection) ? reflections[association] : nil 72: end
Returns a hash containing all AssociationReflection objects for the current class. Example:
Invoice.reflections Account.reflections
# File lib/active_record/reflection.rb, line 33 33: def reflections 34: read_inheritable_attribute(:reflections) || write_inheritable_attribute(:reflections, {}) 35: end
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