From be9b68038e83a617eb38c26147659162e4ac3d2c Mon Sep 17 00:00:00 2001 From: Sean Griffin Date: Tue, 20 Jan 2015 14:09:53 -0700 Subject: Introduce `ActiveRecord::Base#accessed_fields` MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit This method can be used to see all of the fields on a model which have been read. This can be useful during development mode to quickly find out which fields need to be selected. For performance critical pages, if you are not using all of the fields of a database, an easy performance win is only selecting the fields which you need. By calling this method at the end of a controller action, it's easy to determine which fields need to be selected. While writing this, I also noticed a place for an easy performance win internally which I had been wanting to introduce. You cannot mutate a field which you have not read. Therefore, we can skip the calculation of in place changes if we have never read from the field. This can significantly speed up methods like `#changed?` if any of the fields have an expensive mutable type (like `serialize`) ``` Calculating ------------------------------------- #changed? with serialized column (before) 391.000 i/100ms #changed? with serialized column (after) 1.514k i/100ms ------------------------------------------------- #changed? with serialized column (before) 4.243k (± 3.7%) i/s - 21.505k #changed? with serialized column (after) 16.789k (± 3.2%) i/s - 84.784k ``` --- activerecord/CHANGELOG.md | 6 ++++ activerecord/lib/active_record/attribute.rb | 6 +++- .../lib/active_record/attribute_methods.rb | 33 ++++++++++++++++++++++ activerecord/lib/active_record/attribute_set.rb | 4 +++ activerecord/test/cases/attribute_methods_test.rb | 10 +++++++ activerecord/test/cases/attribute_set_test.rb | 11 ++++++++ activerecord/test/cases/attribute_test.rb | 19 +++++++++++++ 7 files changed, 88 insertions(+), 1 deletion(-) (limited to 'activerecord') diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md index d5c141630e..45c3cb0690 100644 --- a/activerecord/CHANGELOG.md +++ b/activerecord/CHANGELOG.md @@ -1,3 +1,9 @@ +* Add `ActiveRecord::Base#accessed_fields`, which can be used to quickly + discover which fields were read from a model when you are looking to only + select the data you need from the database. + + *Sean Griffin* + * Introduce the `:if_exists` option for `drop_table`. Example: diff --git a/activerecord/lib/active_record/attribute.rb b/activerecord/lib/active_record/attribute.rb index 51e4fae62e..73bb059495 100644 --- a/activerecord/lib/active_record/attribute.rb +++ b/activerecord/lib/active_record/attribute.rb @@ -51,7 +51,7 @@ module ActiveRecord end def changed_in_place_from?(old_value) - type.changed_in_place?(old_value, value) + has_been_read? && type.changed_in_place?(old_value, value) end def with_value_from_user(value) @@ -78,6 +78,10 @@ module ActiveRecord false end + def has_been_read? + defined?(@value) + end + def ==(other) self.class == other.class && name == other.name && diff --git a/activerecord/lib/active_record/attribute_methods.rb b/activerecord/lib/active_record/attribute_methods.rb index 8f165fb1dc..b2db0ceae7 100644 --- a/activerecord/lib/active_record/attribute_methods.rb +++ b/activerecord/lib/active_record/attribute_methods.rb @@ -369,6 +369,39 @@ module ActiveRecord write_attribute(attr_name, value) end + # Returns the name of all database fields which have been read from this + # model. This can be useful in devleopment mode to determine which fields + # need to be selected. For performance critical pages, selecting only the + # required fields can be an easy performance win (assuming you aren't using + # all of the fields on the model). + # + # For example: + # + # class PostsController < ActionController::Base + # after_action :print_accessed_fields, only: :index + # + # def index + # @posts = Post.all + # end + # + # private + # + # def print_accessed_fields + # p @posts.first.accessed_fields + # end + # end + # + # Which allows you to quickly change your code to: + # + # class PostsController < ActionController::Base + # def index + # @posts = Post.select(:id, :title, :author_id, :updated_at) + # end + # end + def accessed_fields + @attributes.accessed + end + protected def clone_attribute_value(reader_method, attribute_name) # :nodoc: diff --git a/activerecord/lib/active_record/attribute_set.rb b/activerecord/lib/active_record/attribute_set.rb index 66fcaf6945..fdce68ce45 100644 --- a/activerecord/lib/active_record/attribute_set.rb +++ b/activerecord/lib/active_record/attribute_set.rb @@ -64,6 +64,10 @@ module ActiveRecord end end + def accessed + attributes.select { |_, attr| attr.has_been_read? }.keys + end + protected attr_reader :attributes diff --git a/activerecord/test/cases/attribute_methods_test.rb b/activerecord/test/cases/attribute_methods_test.rb index 4036294121..ea2b94cbf4 100644 --- a/activerecord/test/cases/attribute_methods_test.rb +++ b/activerecord/test/cases/attribute_methods_test.rb @@ -937,6 +937,16 @@ class AttributeMethodsTest < ActiveRecord::TestCase assert model.id_came_from_user? end + def test_accessed_fields + model = @target.first + + assert_equal [], model.accessed_fields + + model.title + + assert_equal ["title"], model.accessed_fields + end + private def new_topic_like_ar_class(&block) diff --git a/activerecord/test/cases/attribute_set_test.rb b/activerecord/test/cases/attribute_set_test.rb index ba53612d30..8025c7c4d2 100644 --- a/activerecord/test/cases/attribute_set_test.rb +++ b/activerecord/test/cases/attribute_set_test.rb @@ -186,5 +186,16 @@ module ActiveRecord attributes.freeze assert_equal({ foo: "1" }, attributes.to_hash) end + + test "#accessed_attributes returns only attributes which have been read" do + builder = AttributeSet::Builder.new(foo: Type::Value.new, bar: Type::Value.new) + attributes = builder.build_from_database(foo: "1", bar: "2") + + assert_equal [], attributes.accessed + + attributes.fetch_value(:foo) + + assert_equal [:foo], attributes.accessed + end end end diff --git a/activerecord/test/cases/attribute_test.rb b/activerecord/test/cases/attribute_test.rb index 39a976fcc8..eac73e11e8 100644 --- a/activerecord/test/cases/attribute_test.rb +++ b/activerecord/test/cases/attribute_test.rb @@ -169,5 +169,24 @@ module ActiveRecord second = Attribute.from_user(:foo, 1, Type::Integer.new) assert_not_equal first, second end + + test "an attribute has not been read by default" do + attribute = Attribute.from_database(:foo, 1, Type::Value.new) + assert_not attribute.has_been_read? + end + + test "an attribute has been read when its value is calculated" do + attribute = Attribute.from_database(:foo, 1, Type::Value.new) + attribute.value + assert attribute.has_been_read? + end + + test "an attribute can not be mutated if it has not been read, + and skips expensive calculations" do + type_which_raises_from_all_methods = Object.new + attribute = Attribute.from_database(:foo, "bar", type_which_raises_from_all_methods) + + assert_not attribute.changed_in_place_from?("bar") + end end end -- cgit v1.2.3