Modify update_all to use a sub select query in some cases:

- In rails@216b37b,
  we attempted a fix let `update_all` use a subselect query instead
  of the `UPDATE FROM` scheme when a LEFT JOIN is used.

  This fix doesn't apply however for leading joings that get
  produced by a `through :table` which first creates
  a INNER JOIN, and then other joins given by the user.
  So such code `Post.through_comments.left_joins(:author)` will
  continue to try using the `UPDATE FROM` scheme and this won't work
  (see the commit mentioned above why).

  The fix in this commit checks whether there is a left join on the
  target, no matter whether it's the first join, and in such case
  makes `update_all` uses a subselect query.

Author: Edouard-chin

activerecord/lib/arel/visitors/postgresql.rb

@@ -64,7 +64,7 @@ def prepare_update_statement(o)
             # The PostgreSQL dialect isn't flexible enough to allow anything other than a inner join
             # for the first join:
             #   UPDATE table SET .. FROM joined_table WHERE ...
-            (o.relation.right.first.is_a?(Arel::Nodes::InnerJoin))
+            (o.relation.right.all? { |join| join.is_a?(Arel::Nodes::InnerJoin) || join.right.expr.right.relation != o.relation.left })
             o
           else
             super

activerecord/lib/arel/visitors/sqlite.rb

@@ -64,7 +64,7 @@ def prepare_update_statement(o)
             # The SQLite3 dialect isn't flexible enough to allow anything other than a inner join
             # for the first join:
             #   UPDATE table SET .. FROM joined_table WHERE ...
-            (o.relation.right.first.is_a?(Arel::Nodes::InnerJoin))
+            (o.relation.right.all? { |join| join.is_a?(Arel::Nodes::InnerJoin) || join.right.expr.right.relation != o.relation.left })
             o
           else
             super

activerecord/test/cases/relation/update_all_test.rb

@@ -13,16 +13,19 @@
 require "models/post"
 require "models/person"
 require "models/pet"
+require "models/pet_treasure"
+require "models/ship"
 require "models/toy"
 require "models/topic"
+require "models/treasure"
 require "models/tag"
 require "models/tagging"
 require "models/warehouse_thing"
 require "models/cpk"
 
 class UpdateAllTest < ActiveRecord::TestCase
   fixtures :authors, :author_addresses, :comments, :companies, :developers, :owners, :posts, :people, :pets, :toys, :tags,
-    :taggings, "warehouse-things", :cpk_orders, :cpk_order_agreements
+    :taggings, :treasures, "warehouse-things", :cpk_orders, :cpk_order_agreements
 
   class TopicWithCallbacks < ActiveRecord::Base
     self.table_name = :topics
@@ -105,6 +108,16 @@ def test_dynamic_update_all_with_one_joined_table
     end
   end
 
+  def test_dynamic_update_all_with_a_through_join
+    pet = pets(:parrot)
+    treasure = treasures(:diamond)
+
+    PetTreasure.create(pet: pet, treasure: treasure)
+
+    assert_operator pet.treasures.left_joins(:ship).update_all(name: "Gold"), :>, 0
+    assert_equal("Gold", treasure.reload.name)
+  end
+
   def test_dynamic_update_all_with_one_join_on_the_target_and_one_indirect_join
     update_fragment = if current_adapter?(:TrilogyAdapter, :Mysql2Adapter)
       "toys.name = owners.name"