Improve `select_one` in `Mysql2Adapter`

Avoid instanciate `ActiveRecord::Result` and calling
`ActiveRecord::Result#hash_rows` for the performance.

2 files changed, 16 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
index f4686b680c..7fbe2307c7 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
@@ -127,6 +127,16 @@ module ActiveRecord
       #   execute(sql, name).map { |row| row.first }
       # end
 
+      # Returns a record hash with the column names as keys and column values
+      # as values.
+      def select_one(arel, name = nil, binds = [])
+        arel, binds = binds_from_relation(arel, binds)
+        execute(to_sql(arel, binds), name).each(as: :hash) do |row|
+          @connection.next_result while @connection.more_results?
+          return row
+        end
+      end
+
       # Returns an array of arrays containing the field values.
       # Order is the same as that returned by +columns+.
       def select_rows(sql, name = nil, binds = [])
diff --git a/activerecord/test/cases/adapters/mysql2/sp_test.rb b/activerecord/test/cases/adapters/mysql2/sp_test.rb
index cdaa2cca44..4197ba45f1 100644
--- a/activerecord/test/cases/adapters/mysql2/sp_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/sp_test.rb
@@ -22,6 +22,12 @@ class Mysql2StoredProcedureTest < ActiveRecord::Mysql2TestCase
     assert @connection.active?, "Bad connection use by 'Mysql2Adapter.select_rows'"
   end
 
+  def test_multi_results_from_select_one
+    row = @connection.select_one('CALL topics(1);')
+    assert_equal 'David', row['author_name']
+    assert @connection.active?, "Bad connection use by 'Mysql2Adapter.select_one'"
+  end
+
   def test_multi_results_from_find_by_sql
     topics = Topic.find_by_sql 'CALL topics(3);'
     assert_equal 3, topics.size