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 23 23: def create_reflection(macro, name, options, active_record) 24: case macro 25: when :has_many, :belongs_to, :has_one, :has_and_belongs_to_many 26: klass = options[:through] ? ThroughReflection : AssociationReflection 27: reflection = klass.new(macro, name, options, active_record) 28: when :composed_of 29: reflection = AggregateReflection.new(macro, name, options, active_record) 30: end 31: 32: self.reflections = self.reflections.merge(name => reflection) 33: reflection 34: 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 45 45: def reflect_on_aggregation(aggregation) 46: reflections[aggregation].is_a?(AggregateReflection) ? reflections[aggregation] : nil 47: end
Returns an array of AggregateReflection objects for all the aggregations in the class.
# File lib/active_record/reflection.rb, line 37 37: def reflect_on_all_aggregations 38: reflections.values.grep(AggregateReflection) 39: 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 59 59: def reflect_on_all_associations(macro = nil) 60: association_reflections = reflections.values.grep(AssociationReflection) 61: macro ? association_reflections.select { |reflection| reflection.macro == macro } : association_reflections 62: end
Returns an array of AssociationReflection objects for all associations which have :autosave enabled.
# File lib/active_record/reflection.rb, line 74 74: def reflect_on_all_autosave_associations 75: reflections.values.select { |reflection| reflection.options[:autosave] } 76: 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 69 69: def reflect_on_association(association) 70: reflections[association].is_a?(AssociationReflection) ? reflections[association] : nil 71: end
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