teaching the mysql adapter how to typecast strings returned from the database

activerecord/lib/active_record/connection_adapters/mysql_adapter.rb

@@ -298,6 +298,127 @@ module ActiveRecord
         @connection.insert_id
       end
 
+      class Result < ActiveRecord::Result
+        def initialize(columns, rows, column_types)
+          super(columns, rows)
+          @column_types = column_types
+        end
+      end
+
+      module Fields
+        class Type
+          def type; end
+
+          def type_cast_for_write(value)
+            value
+          end
+        end
+
+        class Identity < Type
+          def type_cast(value); value; end
+        end
+
+        class Integer < Type
+          def type_cast(value)
+            return if value.nil?
+
+            value.to_i rescue value ? 1 : 0
+          end
+        end
+
+        class Date < Type
+          def type; :date; end
+
+          def type_cast(value)
+            return if value.nil?
+
+            # FIXME: probably we can improve this since we know it is mysql
+            # specific
+            ConnectionAdapters::Column.value_to_date value
+          end
+        end
+
+        class DateTime < Type
+          def type; :datetime; end
+
+          def type_cast(value)
+            return if value.nil?
+
+            # FIXME: probably we can improve this since we know it is mysql
+            # specific
+            ConnectionAdapters::Column.string_to_time value
+          end
+        end
+
+        class Time < Type
+          def type; :time; end
+
+          def type_cast(value)
+            return if value.nil?
+
+            # FIXME: probably we can improve this since we know it is mysql
+            # specific
+            ConnectionAdapters::Column.string_to_dummy_time value
+          end
+        end
+
+        class Float < Type
+          def type; :float; end
+
+          def type_cast(value)
+            return if value.nil?
+
+            value.to_f
+          end
+        end
+
+        class Decimal < Type
+          def type_cast(value)
+            return if value.nil?
+
+            ConnectionAdapters::Column.value_to_decimal value
+          end
+        end
+
+        class Boolean < Type
+          def type_cast(value)
+            return if value.nil?
+
+            ConnectionAdapters::Column.value_to_boolean value
+          end
+        end
+
+        TYPES = {}
+
+        # Register an MySQL +type_id+ with a typcasting object in
+        # +type+.
+        def self.register_type(type_id, type)
+          TYPES[type_id] = type
+        end
+
+        def self.alias_type(new, old)
+          TYPES[new] = TYPES[old]
+        end
+
+        register_type Mysql::Field::TYPE_TINY,    Fields::Boolean.new
+        register_type Mysql::Field::TYPE_LONG,    Fields::Integer.new
+        alias_type Mysql::Field::TYPE_LONGLONG,   Mysql::Field::TYPE_LONG
+        alias_type Mysql::Field::TYPE_NEWDECIMAL, Mysql::Field::TYPE_LONG
+
+        register_type Mysql::Field::TYPE_VAR_STRING, Fields::Identity.new
+        register_type Mysql::Field::TYPE_BLOB, Fields::Identity.new
+        register_type Mysql::Field::TYPE_DATE, Fields::Date.new
+        register_type Mysql::Field::TYPE_DATETIME, Fields::DateTime.new
+        register_type Mysql::Field::TYPE_TIME, Fields::Time.new
+        register_type Mysql::Field::TYPE_FLOAT, Fields::Float.new
+
+        Mysql::Field.constants.grep(/TYPE/).map { |class_name|
+          Mysql::Field.const_get class_name
+        }.reject { |const| TYPES.key? const }.each do |const|
+          register_type const, Fields::Identity.new
+        end
+      end
+
       def exec_without_stmt(sql, name = 'SQL') # :nodoc:
         # Some queries, like SHOW CREATE TABLE don't work through the prepared
         # statement API. For those queries, we need to use this method. :'(
@@ -306,8 +427,17 @@ module ActiveRecord
           affected_rows = @connection.affected_rows
 
           if result
-            cols = result.fetch_fields.map { |field| field.name }
-            result_set = ActiveRecord::Result.new(cols, result.to_a)
+            types = {}
+            result.fetch_fields.each { |field|
+              if field.decimals > 0
+                types[field.name] = Fields::Decimal.new
+              else
+                types[field.name] = Fields::TYPES.fetch(field.type) {
+                  Fields::Identity.new
+                }
+              end
+            }
+            result_set = Result.new(types.keys, result.to_a, types)
             result.free
           else
             result_set = ActiveRecord::Result.new([], [])

activerecord/test/cases/calculations_test.rb

@@ -433,7 +433,7 @@ class CalculationsTest < ActiveRecord::TestCase
     Company.create!(:name => "test", :contracts => [Contract.new(:developer_id => 7)])
 
     # TODO: Investigate why PG isn't being typecast
-    if current_adapter?(:PostgreSQLAdapter)
+    if current_adapter?(:PostgreSQLAdapter) || current_adapter?(:MysqlAdapter)
       assert_equal "7", Company.includes(:contracts).maximum(:developer_id)
     else
       assert_equal 7, Company.includes(:contracts).maximum(:developer_id)
@@ -444,7 +444,7 @@ class CalculationsTest < ActiveRecord::TestCase
     Company.create!(:name => "test", :contracts => [Contract.new(:developer_id => 7)])
 
     # TODO: Investigate why PG isn't being typecast
-    if current_adapter?(:PostgreSQLAdapter)
+    if current_adapter?(:PostgreSQLAdapter) || current_adapter?(:MysqlAdapter)
       assert_equal "7", Company.includes(:contracts).minimum(:developer_id)
     else
       assert_equal 7, Company.includes(:contracts).minimum(:developer_id)