From 3b9982a3b778b63488975eb03592d33aa9fb04dd Mon Sep 17 00:00:00 2001
From: Tekin Suleyman <tekin@tekin.co.uk>
Date: Sat, 17 Nov 2018 13:50:01 -0800
Subject: Make implicit order column configurable
When calling ordered finder methods such as +first+ or +last+ without an
explicit order clause, ActiveRecord sorts records by primary key. This
can result in unpredictable and surprising behaviour when the primary
key is not an auto-incrementing integer, for example when it's a UUID.
This change makes it possible to override the column used for implicit
ordering such that +first+ and +last+ will return more predictable
results. For Example:
class Project < ActiveRecord::Base
self.implicit_order_column = "created_at"
end
---
activerecord/CHANGELOG.md | 17 +++++++++++++++++
activerecord/lib/active_record/model_schema.rb | 16 ++++++++++++++++
.../lib/active_record/relation/finder_methods.rb | 4 ++--
activerecord/test/cases/finder_test.rb | 10 ++++++++++
4 files changed, 45 insertions(+), 2 deletions(-)
diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 6186595a56..13cc486e7f 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,20 @@
+* Make the implicit order column configurable.
+
+ When calling ordered finder methods such as +first+ or +last+ without an
+ explicit order clause, ActiveRecord sorts records by primary key. This can
+ result in unpredictable and surprising behaviour when the primary key is
+ not an auto-incrementing integer, for example when it's a UUID. This change
+ makes it possible to override the column used for implicit ordering such
+ that +first+ and +last+ will return more predictable results.
+
+ Example:
+
+ class Project < ActiveRecord::Base
+ self.implicit_order_column = "created_at"
+ end
+
+ *Tekin Suleyman*
+
* Bump minimum PostgreSQL version to 9.3.
*Yasuo Honda*
diff --git a/activerecord/lib/active_record/model_schema.rb b/activerecord/lib/active_record/model_schema.rb
index c50a420432..55fc58e339 100644
--- a/activerecord/lib/active_record/model_schema.rb
+++ b/activerecord/lib/active_record/model_schema.rb
@@ -102,6 +102,21 @@ module ActiveRecord
# If true, the default table name for a Product class will be "products". If false, it would just be "product".
# See table_name for the full rules on table/class naming. This is true, by default.
+ ##
+ # :singleton-method: implicit_order_column
+ # :call-seq: implicit_order_column
+ #
+ # The name of the column records are ordered by if no explicit order clause
+ # is used during an ordered finder call. If not set the primary key is used.
+
+ ##
+ # :singleton-method: implicit_order_column=
+ # :call-seq: implicit_order_column=(column_name)
+ #
+ # Sets the column to sort records by when no explicit order clause is used
+ # during an ordered finder call. Useful when the primary key is not an
+ # auto-incrementing integer, for example when it's a UUID. Note that using
+ # a non-unique column can result in non-deterministic results.
included do
mattr_accessor :primary_key_prefix_type, instance_writer: false
@@ -110,6 +125,7 @@ module ActiveRecord
class_attribute :schema_migrations_table_name, instance_accessor: false, default: "schema_migrations"
class_attribute :internal_metadata_table_name, instance_accessor: false, default: "ar_internal_metadata"
class_attribute :pluralize_table_names, instance_writer: false, default: true
+ class_attribute :implicit_order_column, instance_accessor: false
self.protected_environments = ["production"]
self.inheritance_column = "type"
diff --git a/activerecord/lib/active_record/relation/finder_methods.rb b/activerecord/lib/active_record/relation/finder_methods.rb
index afaa900442..dc03b196f4 100644
--- a/activerecord/lib/active_record/relation/finder_methods.rb
+++ b/activerecord/lib/active_record/relation/finder_methods.rb
@@ -550,8 +550,8 @@ module ActiveRecord
end
def ordered_relation
- if order_values.empty? && primary_key
- order(arel_attribute(primary_key).asc)
+ if order_values.empty? && (implicit_order_column || primary_key)
+ order(arel_attribute(implicit_order_column || primary_key).asc)
else
self
end
diff --git a/activerecord/test/cases/finder_test.rb b/activerecord/test/cases/finder_test.rb
index 52fd9291b2..21e84d850b 100644
--- a/activerecord/test/cases/finder_test.rb
+++ b/activerecord/test/cases/finder_test.rb
@@ -741,6 +741,16 @@ class FinderTest < ActiveRecord::TestCase
assert_equal expected, clients.limit(5).first(2)
end
+ def test_implicit_order_column_is_configurable
+ old_implicit_order_column = Topic.implicit_order_column
+ Topic.implicit_order_column = "title"
+
+ assert_equal topics(:fifth), Topic.first
+ assert_equal topics(:third), Topic.last
+ ensure
+ Topic.implicit_order_column = old_implicit_order_column
+ end
+
def test_take_and_first_and_last_with_integer_should_return_an_array
assert_kind_of Array, Topic.take(5)
assert_kind_of Array, Topic.first(5)
--
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