From 2d73f5ae2fe75427d56853f107abda21754f1b1a Mon Sep 17 00:00:00 2001 From: Godfrey Chan Date: Wed, 21 May 2014 23:36:35 -0700 Subject: Fixed serialization for records with an attribute named `format`. * * * This bug can be triggered when serializing record R (the instance) of type C (the class), provided that the following conditions are met: 1. The name of one or more columns/attributes on C/R matches an existing private method on C (e.g. those defined by `Kernel`, such as `format`). 2. The attribute methods have not yet been generated on C. In this case, the matching private methods will be called by the serialization code (with no arguments) and their return values will be serialized instead. If the method requires one or more arguments, it will result in an `ArgumentError`. This regression is introduced in d1316bb. * * * Attribute methods (e.g. `#name` and `#format`, assuming the class has columns named `name` and `format` in its database table) are lazily defined. Instead of defining them when a the class is defined (e.g. in the `inherited` hook on `ActiveRecord::Base`), this operation is deferred until they are first accessed. The reason behind this is that is defining those methods requires knowing what columns are defined on the database table, which usually requires a round-trip to the database. Deferring their definition until the last-possible moment helps reducing unnessary work, especially in development mode where classes are redefined and throw away between requests. Typically, when an attribute is first accessed (e.g. `a_book.format`), it will fire the `method_missing` hook on the class, which triggers the definition of the attribute methods. This even works for methods like `format`, because calling a private method with an explicit receiver will also trigger that hook. Unfortunately, `read_attribute_for_serialization` is simply an alias to `send`, which does not respect method visibility. As a result, when serializing a record with those conflicting attributes, the `method_missing` is not fired, and as a result the attribute methods are not defined one would expected. Before d1316bb, this is negated by the fact that calling the `run_callbacks` method will also trigger a call to `respond_to?`, which is another trigger point for the class to define its attribute methods. Therefore, when Active Record tries to run the `after_find` callbacks, it will also define all the attribute methods thus masking the problem. * * * The proper fix for this problem is probably to restrict `read_attribute_for_serialization` to call public methods only (i.e. alias `read_attribute_for_serialization` to `public_send` instead of `send`). This however would be quite risky to change in a patch release and would probably require a full deprecation cycle. Another approach would be to override `read_attribute_for_serialization` inside Active Record to force the definition of attribute methods: def read_attribute_for_serialization(attribute) self.class.define_attribute_methods send(attribute) end Unfortunately, this is quite likely going to cause a performance degradation. This patch therefore restores the behaviour from the 4-0-stable branch by explicitly forcing the class to define its attribute methods in a similar spot (when records are initialized). This should not cause any extra roundtrips to the database because the `@columns` should already be cached on the class. Fixes #15188. --- activerecord/CHANGELOG.md | 6 ++++++ activerecord/lib/active_record/core.rb | 2 ++ activerecord/test/cases/serialization_test.rb | 19 +++++++++++++++++++ activerecord/test/fixtures/books.yml | 2 ++ activerecord/test/schema/schema.rb | 1 + 5 files changed, 30 insertions(+) diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md index 3dd973d64b..260bd063aa 100644 --- a/activerecord/CHANGELOG.md +++ b/activerecord/CHANGELOG.md @@ -1,3 +1,9 @@ +* Fixed serialization for records with an attribute named `format`. + + Fixes #15188. + + *Godfrey Chan* + * When a `group` is set, `sum`, `size`, `average`, `minimum` and `maximum` on a NullRelation should return a Hash. diff --git a/activerecord/lib/active_record/core.rb b/activerecord/lib/active_record/core.rb index 4571cc0786..07eafef788 100644 --- a/activerecord/lib/active_record/core.rb +++ b/activerecord/lib/active_record/core.rb @@ -286,6 +286,8 @@ module ActiveRecord @new_record = false + self.class.define_attribute_methods + run_callbacks :find run_callbacks :initialize diff --git a/activerecord/test/cases/serialization_test.rb b/activerecord/test/cases/serialization_test.rb index c46060a646..7dd1f10ce9 100644 --- a/activerecord/test/cases/serialization_test.rb +++ b/activerecord/test/cases/serialization_test.rb @@ -1,8 +1,11 @@ require "cases/helper" require 'models/contact' require 'models/topic' +require 'models/book' class SerializationTest < ActiveRecord::TestCase + fixtures :books + FORMATS = [ :xml, :json ] def setup @@ -65,4 +68,20 @@ class SerializationTest < ActiveRecord::TestCase ensure ActiveRecord::Base.include_root_in_json = original_root_in_json end + + def test_read_attribute_for_serialization_with_format_after_init + klazz = Class.new(ActiveRecord::Base) + klazz.table_name = 'books' + + book = klazz.new(format: 'paperback') + assert_equal 'paperback', book.read_attribute_for_serialization(:format) + end + + def test_read_attribute_for_serialization_with_format_after_find + klazz = Class.new(ActiveRecord::Base) + klazz.table_name = 'books' + + book = klazz.find(books(:awdr).id) + assert_equal 'paperback', book.read_attribute_for_serialization(:format) + end end diff --git a/activerecord/test/fixtures/books.yml b/activerecord/test/fixtures/books.yml index fb48645456..abe56752c6 100644 --- a/activerecord/test/fixtures/books.yml +++ b/activerecord/test/fixtures/books.yml @@ -2,8 +2,10 @@ awdr: author_id: 1 id: 1 name: "Agile Web Development with Rails" + format: "paperback" rfr: author_id: 1 id: 2 name: "Ruby for Rails" + format: "ebook" diff --git a/activerecord/test/schema/schema.rb b/activerecord/test/schema/schema.rb index 8c52ad2724..c15ee5022e 100644 --- a/activerecord/test/schema/schema.rb +++ b/activerecord/test/schema/schema.rb @@ -103,6 +103,7 @@ ActiveRecord::Schema.define do create_table :books, force: true do |t| t.integer :author_id + t.string :format t.column :name, :string t.column :status, :integer, default: 0 t.column :read_status, :integer, default: 0 -- cgit v1.2.3 From 28d52c59f2cb32180ca24770bf95597ea3ad8198 Mon Sep 17 00:00:00 2001 From: Godfrey Chan Date: Thu, 22 May 2014 11:58:20 -0700 Subject: Avoid slowing down AR object initialization 2d73f5a forces AR to enter the `define_attribute_methods` method whenever it instantiate a record from the `init_with` entry point. This is a potential performance hotspot, because `init_with` is called from all `find*` family methods, and `define_attribute_methods` is slow because it tries to acquire a lock on the mutex everytime it is entered. By using [DCL](http://en.wikipedia.org/wiki/Double-checked_locking), we can avoid grabbing the lock most of the time when the attribute methods are already defined (the common case). This is made possible by the fact that reading an instance variable is an atomic operation in Ruby. Credit goes to Aaron Patterson for pointing me to DCL and filling me in on the atomicity guarantees in Ruby. [*Godfrey Chan*, *Aaron Patterson*] --- activerecord/lib/active_record/attribute_methods.rb | 1 + 1 file changed, 1 insertion(+) diff --git a/activerecord/lib/active_record/attribute_methods.rb b/activerecord/lib/active_record/attribute_methods.rb index 6c2403d87e..b9141b9b33 100644 --- a/activerecord/lib/active_record/attribute_methods.rb +++ b/activerecord/lib/active_record/attribute_methods.rb @@ -66,6 +66,7 @@ module ActiveRecord # Generates all the attribute related methods for columns in the database # accessors, mutators and query methods. def define_attribute_methods # :nodoc: + return false if @attribute_methods_generated # Use a mutex; we don't want two thread simultaneously trying to define # attribute methods. generated_attribute_methods.synchronize do -- cgit v1.2.3