Module: ActiveRecord::AttributeMethods::Read

Extended by:
ActiveSupport::Concern
Defined in:
activerecord/lib/active_record/attribute_methods/read.rb

Defined Under Namespace

Modules: ClassMethods

Constant Summary collapse

ReaderMethodCache =
Class.new(AttributeMethodCache) {
  private
  # We want to generate the methods via module_eval rather than
  # define_method, because define_method is slower on dispatch.
  # Evaluating many similar methods may use more memory as the instruction
  # sequences are duplicated and cached (in MRI).  define_method may
  # be slower on dispatch, but if you're careful about the closure
  # created, then define_method will consume much less memory.
  #
  # 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.
  #
  # We are also defining a constant to hold the frozen string of
  # the attribute name. Using a constant means that we do not have
  # to allocate an object on each call to the attribute method.
  # Making it frozen means that it doesn't get duped when used to
  # key the @attributes_cache in read_attribute.
  def method_body(method_name, const_name)
    <<-EOMETHOD
    def #{method_name}
      name = ::ActiveRecord::AttributeMethods::AttrNames::ATTR_#{const_name}
      read_attribute(name) { |n| missing_attribute(n, caller) }
    end
    EOMETHOD
  end
}.new
ATTRIBUTE_TYPES_CACHED_BY_DEFAULT =
[:datetime, :timestamp, :time, :date]

Instance Method Summary collapse

Methods included from ActiveSupport::Concern

append_features, extended, included

Instance Method Details

#read_attribute(attr_name) ⇒ Object

Returns the value of the attribute identified by attr_name 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)).


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# File 'activerecord/lib/active_record/attribute_methods/read.rb', line 107

def read_attribute(attr_name)
  # If it's cached, just return it
  # We use #[] first as a perf optimization for non-nil values. See https://gist.github.com/jonleighton/3552829.
  name = attr_name.to_s
  @attributes_cache[name] || @attributes_cache.fetch(name) {
    column = @columns_hash.fetch(name) {
      return @attributes.fetch(name) {
        if name == 'id' && self.class.primary_key != name
          read_attribute(self.class.primary_key)
        end
      }
    }

    value = @attributes.fetch(name) {
      return block_given? ? yield(name) : nil
    }

    if self.class.cache_attribute?(name)
      @attributes_cache[name] = column.type_cast(value)
    else
      column.type_cast value
    end
  }
end