Merge pull request #22803 from kamipo/improve_select_one_in_mysql2_adapter

Improve `select_one` in `Mysql2Adapter`

activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb

@@ -99,33 +99,15 @@ def disconnect!
       # DATABASE STATEMENTS ======================================
       #++
 
-      # FIXME: re-enable the following once a "better" query_cache solution is in core
-      #
-      # The overrides below perform much better than the originals in AbstractAdapter
-      # because we're able to take advantage of mysql2's lazy-loading capabilities
-      #
-      # # Returns a record hash with the column names as keys and column values
-      # # as values.
-      # def select_one(sql, name = nil)
-      #   result = execute(sql, name)
-      #   result.each(as: :hash) do |r|
-      #     return r
-      #   end
-      # end
-      #
-      # # Returns a single value from a record
-      # def select_value(sql, name = nil)
-      #   result = execute(sql, name)
-      #   if first = result.first
-      #     first.first
-      #   end
-      # end
-      #
-      # # Returns an array of the values of the first column in a select:
-      # #   select_values("SELECT id FROM companies LIMIT 3") => [1,2,3]
-      # def select_values(sql, name = nil)
-      #   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+.

activerecord/test/cases/adapters/mysql2/sp_test.rb

@@ -22,6 +22,12 @@ def test_multi_results
     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