Returns true if the provided attribute is being cached.
# File lib/active_record/attribute_methods/read.rb, line 28 def cache_attribute?(attr_name) cached_attributes.include?(attr_name) end
cache_attributes allows you to declare which converted attribute values should be cached. Usually caching only pays off for attributes with expensive conversion methods, like time related columns (e.g. created_at, updated_at).
# File lib/active_record/attribute_methods/read.rb, line 17 def cache_attributes(*attribute_names) cached_attributes.merge attribute_names.map { |attr| attr.to_s } end
Returns the attributes which are cached. By default time related columns with datatype :datetime, :timestamp, :time, :date are cached.
# File lib/active_record/attribute_methods/read.rb, line 23 def cached_attributes @cached_attributes ||= columns.select { |c| cacheable_column?(c) }.map { |col| col.name }.to_set end
We want to generate the methods via module_eval rather than define_method, because define_method is slower on dispatch and uses more memory (because it creates a closure).
But sometimes the database might return columns with characters that are not allowed in normal method names (like 'my_column(omg)'. So to work around this we first define with the __temp__ identifier, and then use alias method to rename it to what we want.
# File lib/active_record/attribute_methods/read.rb, line 69 def define_method_attribute(attr_name) generated_attribute_methods.module_eval def __temp__ #{internal_attribute_access_code(attr_name, attribute_cast_code(attr_name))} end alias_method '#{attr_name}', :__temp__ undef_method :__temp__, __FILE__, __LINE__ + 1 end
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