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require 'active_record/attributes/translator'
module ActiveRecord
module AttributeMethods
module Read
extend ActiveSupport::Concern
ATTRIBUTE_TYPES_CACHED_BY_DEFAULT = [:datetime, :timestamp, :time, :date]
included do
config_attribute :attribute_types_cached_by_default, :global => true
self.attribute_types_cached_by_default = ATTRIBUTE_TYPES_CACHED_BY_DEFAULT
end
module ClassMethods
# +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+).
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 <tt>:datetime, :timestamp, :time, :date</tt> are cached.
def cached_attributes
@cached_attributes ||= columns.select { |c| cacheable_column?(c) }.map { |col| col.name }.to_set
end
# Returns +true+ if the provided attribute is being cached.
def cache_attribute?(attr_name)
cached_attributes.include?(attr_name)
end
def undefine_attribute_methods
generated_external_attribute_methods.module_eval do
instance_methods.each { |m| undef_method(m) }
end
super
end
def type_cast_attribute(attr_name, attributes, cache = {}) #:nodoc:
return unless attr_name
attr_name = attr_name.to_s
if generated_external_attribute_methods.method_defined?(attr_name)
if attributes.has_key?(attr_name) || attr_name == 'id'
generated_external_attribute_methods.send(attr_name, attributes[attr_name], attributes, cache, attr_name)
end
elsif !attribute_methods_generated?
# If we haven't generated the caster methods yet, do that and
# then try again
define_attribute_methods
type_cast_attribute(attr_name, attributes, cache)
else
# If we get here, the attribute has no associated DB column, so
# just return it verbatim.
attributes[attr_name]
end
end
protected
# 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.
def define_method_attribute(attr_name)
cast_code = attribute_cast_code(attr_name)
generated_attribute_methods.module_eval <<-STR, __FILE__, __LINE__ + 1
def __temp__
#{internal_attribute_access_code(attr_name, cast_code)}
end
alias_method '#{attr_name}', :__temp__
undef_method :__temp__
STR
generated_external_attribute_methods.module_eval <<-STR, __FILE__, __LINE__ + 1
def __temp__(v, attributes, attributes_cache, attr_name)
#{external_attribute_access_code(attr_name, cast_code)}
end
alias_method '#{attr_name}', :__temp__
undef_method :__temp__
STR
end
private
def cacheable_column?(column)
attribute_types_cached_by_default.include?(column.type)
end
def internal_attribute_access_code(attr_name, cast_code)
method = instance_cast_method(attr_name)
if cache_attribute?(attr_name)
"cached_cast_attribute('#{attr_name}', :#{method})"
else
"cast_attribute('#{attr_name}', :#{method})"
end
end
def external_attribute_access_code(attr_name, cast_code)
access_code = "v && #{cast_code}"
if cache_attribute?(attr_name)
access_code = "attributes_cache[attr_name] ||= (#{access_code})"
end
access_code
end
def attribute_cast_code(attr_name)
columns_hash[attr_name].type_cast_code('v')
end
def instance_cast_method(attr_name)
"cast_column"
end
end
# Returns the value of the attribute identified by <tt>attr_name</tt> after it has been typecast (for example,
# "2004-12-12" in a data column is cast to a date object, like Date.new(2004, 12, 12)).
def read_attribute(attr_name)
if @columns_hash.key? attr_name
@columns_hash[attr_name].type_cast @attributes[attr_name]
else
self.class.type_cast_attribute(attr_name, @attributes, @attributes_cache)
end
end
private
def attribute_translator
Attributes::Translator.new(@attributes, @columns_hash)
end
def cached_cast_attribute(attr_name, method)
@attributes_cache[attr_name] ||= cast_attribute(attr_name, method)
end
def cast_attribute(attr_name, method)
attribute_translator.cast_attribute(attr_name, method) do
missing_attribute(attr_name, caller)
end
end
def attribute(attribute_name)
read_attribute(attribute_name)
end
end
end
end
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