Merge pull request rails#25507 from bquorning/optimize-for-first-result-and-remove-mysql-select_one

Remove #select_one from Mysql2Adapter

Author: rafaelfranca

activerecord/lib/active_record/connection_adapters/mysql/database_statements.rb

@@ -13,19 +13,6 @@ def select_all(arel, name = nil, binds = [], preparable: nil)
           result
         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)
-          @connection.query_options.merge!(as: :hash)
-          select_result(to_sql(arel, binds), name, binds) do |result|
-            @connection.next_result while @connection.more_results?
-            result.first
-          end
-        ensure
-          @connection.query_options.merge!(as: :array)
-        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 = [])

activerecord/lib/active_record/result.rb

@@ -75,8 +75,14 @@ def [](idx)
       hash_rows[idx]
     end
 
+    def first
+      return nil if @rows.empty?
+      Hash[@columns.zip(@rows.first)]
+    end
+
     def last
-      hash_rows.last
+      return nil if @rows.empty?
+      Hash[@columns.zip(@rows.last)]
     end
 
     def cast_values(type_overrides = {}) # :nodoc:

activerecord/test/cases/result_test.rb

@@ -22,6 +22,16 @@ def result
       ], result.to_hash
     end
 
+    test "first returns first row as a hash" do
+      assert_equal(
+        {'col_1' => 'row 1 col 1', 'col_2' => 'row 1 col 2'}, result.first)
+    end
+
+    test "last returns last row as a hash" do
+      assert_equal(
+        {'col_1' => 'row 3 col 1', 'col_2' => 'row 3 col 2'}, result.last)
+    end
+
     test "each with block returns row hashes" do
       result.each do |row|
         assert_equal ['col_1', 'col_2'], row.keys