Generate subquery for Relation passed as array condition for where

Instead of executing 2 queries for fetching records filtered by array condition with Relation,
added generation of subquery to current query.

This behaviour will be consistent when passes Relation as hash condition to where

Closes: #12415

4 files changed, 40 insertions, 2 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 83c94caa53..77ce30359c 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,20 @@
+*   Generate subquery for `Relation` if it passed as array condition for `where` method
+
+    Example:
+        # Before
+        Blog.where('id in (?)', Blog.where(id: 1))
+        # =>  SELECT "blogs".* FROM "blogs"  WHERE "blogs"."id" = 1
+        # =>  SELECT "blogs".* FROM "blogs"  WHERE (id IN (1))
+
+        # After
+        Blog.where('id in (?)', Blog.where(id: 1).select(:id))
+        # =>  SELECT "blogs".* FROM "blogs"
+        #     WHERE "blogs"."id" IN (SELECT "blogs"."id" FROM "blogs"  WHERE "blogs"."id" = 1)
+
+    Fixes: #12415
+
+    *Paul Nikitochkin*
+
 *   `has_and_belongs_to_many` is now transparently implemented in terms of
     `has_many :through`.  Behavior should remain the same, if not, it is a bug.
 
diff --git a/activerecord/lib/active_record/sanitization.rb b/activerecord/lib/active_record/sanitization.rb
index 0b87ab9926..af4ea0efec 100644
--- a/activerecord/lib/active_record/sanitization.rb
+++ b/activerecord/lib/active_record/sanitization.rb
@@ -127,7 +127,17 @@ module ActiveRecord
         raise_if_bind_arity_mismatch(statement, statement.count('?'), values.size)
         bound = values.dup
         c = connection
-        statement.gsub('?') { quote_bound_value(bound.shift, c) }
+        statement.gsub('?') do
+          replace_bind_variable(bound.shift, c)
+        end
+      end
+
+      def replace_bind_variable(value, c = connection)
+        if ActiveRecord::Relation === value
+          value.to_sql
+        else
+          quote_bound_value(value, c)
+        end
       end
 
       def replace_named_bind_variables(statement, bind_vars) #:nodoc:
@@ -135,7 +145,7 @@ module ActiveRecord
           if $1 == ':' # skip postgresql casts
             $& # return the whole match
           elsif bind_vars.include?(match = $2.to_sym)
-            quote_bound_value(bind_vars[match])
+            replace_bind_variable(bind_vars[match])
           else
             raise PreparedStatementInvalid, "missing value for :#{match} in #{statement}"
           end
diff --git a/activerecord/test/cases/relations_test.rb b/activerecord/test/cases/relations_test.rb
index f814947ab2..0cd8595ba6 100644
--- a/activerecord/test/cases/relations_test.rb
+++ b/activerecord/test/cases/relations_test.rb
@@ -626,6 +626,11 @@ class RelationTest < ActiveRecord::TestCase
       relation = Author.where(:id => Author.where(:id => david.id))
       assert_equal [david], relation.to_a
     }
+
+    assert_queries(1) {
+      relation = Author.where('id in (?)', Author.where(id: david).select(:id))
+      assert_equal [david], relation.to_a
+    }
   end
 
   def test_find_all_using_where_with_relation_and_alternate_primary_key
diff --git a/activerecord/test/cases/sanitize_test.rb b/activerecord/test/cases/sanitize_test.rb
index 082570c55b..4c0762deca 100644
--- a/activerecord/test/cases/sanitize_test.rb
+++ b/activerecord/test/cases/sanitize_test.rb
@@ -31,4 +31,10 @@ class SanitizeTest < ActiveRecord::TestCase
     assert_equal "name=#{quoted_bambi_and_thumper}", Binary.send(:sanitize_sql_array, ["name=?", "Bambi\nand\nThumper"])
     assert_equal "name=#{quoted_bambi_and_thumper}", Binary.send(:sanitize_sql_array, ["name=?", "Bambi\nand\nThumper".mb_chars])
   end
+
+  def test_sanitize_sql_array_handles_relations
+    assert_match(/\(\bselect\b.*?\bwhere\b.*?\)/i,
+      Binary.send(:sanitize_sql_array, ["id in (?)", Binary.where(id: 1)]),
+      "should sanitize `Relation` as subquery")
+  end
 end