Refactoring attributes/types [#3348 state:resolved]

Signed-off-by: Joshua Peek <josh@joshpeek.com>

16 files changed, 429 insertions, 148 deletions

diff --git a/activerecord/lib/active_record/attribute_methods/before_type_cast.rb b/activerecord/lib/active_record/attribute_methods/before_type_cast.rb
index a4e144f233..74921241f7 100644
--- a/activerecord/lib/active_record/attribute_methods/before_type_cast.rb
+++ b/activerecord/lib/active_record/attribute_methods/before_type_cast.rb
@@ -8,25 +8,18 @@ module ActiveRecord
       end
 
       def read_attribute_before_type_cast(attr_name)
-        @attributes[attr_name]
+        _attributes.without_typecast[attr_name]
       end
 
       # Returns a hash of attributes before typecasting and deserialization.
       def attributes_before_type_cast
-        self.attribute_names.inject({}) do |attrs, name|
-          attrs[name] = read_attribute_before_type_cast(name)
-          attrs
-        end
+        _attributes.without_typecast
       end
 
       private
         # Handle *_before_type_cast for method_missing.
         def attribute_before_type_cast(attribute_name)
-          if attribute_name == 'id'
-            read_attribute_before_type_cast(self.class.primary_key)
-          else
-            read_attribute_before_type_cast(attribute_name)
-          end
+          read_attribute_before_type_cast(attribute_name)
         end
     end
   end
diff --git a/activerecord/lib/active_record/attribute_methods/query.rb b/activerecord/lib/active_record/attribute_methods/query.rb
index a949d80120..0154ee35f8 100644
--- a/activerecord/lib/active_record/attribute_methods/query.rb
+++ b/activerecord/lib/active_record/attribute_methods/query.rb
@@ -8,23 +8,7 @@ module ActiveRecord
       end
 
       def query_attribute(attr_name)
-        unless value = read_attribute(attr_name)
-          false
-        else
-          column = self.class.columns_hash[attr_name]
-          if column.nil?
-            if Numeric === value || value !~ /[^0-9]/
-              !value.to_i.zero?
-            else
-              return false if ActiveRecord::ConnectionAdapters::Column::FALSE_VALUES.include?(value)
-              !value.blank?
-            end
-          elsif column.number?
-            !value.zero?
-          else
-            !value.blank?
-          end
-        end
+        _attributes.has?(attr_name)
       end
 
       private
@@ -35,3 +19,5 @@ module ActiveRecord
     end
   end
 end
+
+
diff --git a/activerecord/lib/active_record/attribute_methods/read.rb b/activerecord/lib/active_record/attribute_methods/read.rb
index 3da3d9d8cc..97caec7744 100644
--- a/activerecord/lib/active_record/attribute_methods/read.rb
+++ b/activerecord/lib/active_record/attribute_methods/read.rb
@@ -37,11 +37,7 @@ module ActiveRecord
 
         protected
           def define_method_attribute(attr_name)
-            if self.serialized_attributes[attr_name]
-              define_read_method_for_serialized_attribute(attr_name)
-            else
-              define_read_method(attr_name.to_sym, attr_name, columns_hash[attr_name])
-            end
+            define_read_method(attr_name.to_sym, attr_name, columns_hash[attr_name])
 
             if attr_name == primary_key && attr_name != "id"
               define_read_method(:id, attr_name, columns_hash[attr_name])
@@ -49,18 +45,12 @@ module ActiveRecord
           end
 
         private
-          # Define read method for serialized attribute.
-          def define_read_method_for_serialized_attribute(attr_name)
-            generated_attribute_methods.module_eval("def #{attr_name}; unserialize_attribute('#{attr_name}'); end", __FILE__, __LINE__)
-          end
 
           # Define an attribute reader method.  Cope with nil column.
           def define_read_method(symbol, attr_name, column)
-            cast_code = column.type_cast_code('v') if column
-            access_code = cast_code ? "(v=@attributes['#{attr_name}']) && #{cast_code}" : "@attributes['#{attr_name}']"
-
+            access_code = "_attributes['#{attr_name}']"
             unless attr_name.to_s == self.primary_key.to_s
-              access_code = access_code.insert(0, "missing_attribute('#{attr_name}', caller) unless @attributes.has_key?('#{attr_name}'); ")
+              access_code = access_code.insert(0, "missing_attribute('#{attr_name}', caller) unless _attributes.key?('#{attr_name}'); ")
             end
 
             if cache_attribute?(attr_name)
@@ -73,38 +63,7 @@ module ActiveRecord
       # Returns the value of the attribute identified by <tt>attr_name</tt> after it has been typecast (for example,
       # "2004-12-12" in a data column is cast to a date object, like Date.new(2004, 12, 12)).
       def read_attribute(attr_name)
-        attr_name = attr_name.to_s
-        attr_name = self.class.primary_key if attr_name == 'id'
-        if !(value = @attributes[attr_name]).nil?
-          if column = column_for_attribute(attr_name)
-            if unserializable_attribute?(attr_name, column)
-              unserialize_attribute(attr_name)
-            else
-              column.type_cast(value)
-            end
-          else
-            value
-          end
-        else
-          nil
-        end
-      end
-
-      # Returns true if the attribute is of a text column and marked for serialization.
-      def unserializable_attribute?(attr_name, column)
-        column.text? && self.class.serialized_attributes[attr_name]
-      end
-
-      # Returns the unserialized object of the attribute.
-      def unserialize_attribute(attr_name)
-        unserialized_object = object_from_yaml(@attributes[attr_name])
-
-        if unserialized_object.is_a?(self.class.serialized_attributes[attr_name]) || unserialized_object.nil?
-          @attributes.frozen? ? unserialized_object : @attributes[attr_name] = unserialized_object
-        else
-          raise SerializationTypeMismatch,
-            "#{attr_name} was supposed to be a #{self.class.serialized_attributes[attr_name]}, but was a #{unserialized_object.class.to_s}"
-        end
+        _attributes[attr_name]
       end
 
       private
diff --git a/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb b/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb
index a8e3e28a7a..4ac0c7f608 100644
--- a/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb
+++ b/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb
@@ -12,48 +12,20 @@ module ActiveRecord
       end
 
       module ClassMethods
+
+        def cache_attribute?(attr_name)
+          time_zone_aware?(attr_name) || super
+        end
+
         protected
-          # Defined for all +datetime+ and +timestamp+ attributes when +time_zone_aware_attributes+ are enabled.
-          # This enhanced read method automatically converts the UTC time stored in the database to the time zone stored in Time.zone.
-          def define_method_attribute(attr_name)
-            if create_time_zone_conversion_attribute?(attr_name, columns_hash[attr_name])
-              method_body = <<-EOV
-                def #{attr_name}(reload = false)
-                  cached = @attributes_cache['#{attr_name}']
-                  return cached if cached && !reload
-                  time = read_attribute('#{attr_name}')
-                  @attributes_cache['#{attr_name}'] = time.acts_like?(:time) ? time.in_time_zone : time
-                end
-              EOV
-              generated_attribute_methods.module_eval(method_body, __FILE__, __LINE__)
-            else
-              super
-            end
-          end
 
-          # Defined for all +datetime+ and +timestamp+ attributes when +time_zone_aware_attributes+ are enabled.
-          # This enhanced write method will automatically convert the time passed to it to the zone stored in Time.zone.
-          def define_method_attribute=(attr_name)
-            if create_time_zone_conversion_attribute?(attr_name, columns_hash[attr_name])
-              method_body = <<-EOV
-                def #{attr_name}=(time)
-                  unless time.acts_like?(:time)
-                    time = time.is_a?(String) ? Time.zone.parse(time) : time.to_time rescue time
-                  end
-                  time = time.in_time_zone rescue nil if time
-                  write_attribute(:#{attr_name}, time)
-                end
-              EOV
-              generated_attribute_methods.module_eval(method_body, __FILE__, __LINE__)
-            else
-              super
-            end
+          def time_zone_aware?(attr_name)
+            column = columns_hash[attr_name]
+            time_zone_aware_attributes &&
+              !skip_time_zone_conversion_for_attributes.include?(attr_name.to_sym) &&
+                [:datetime, :timestamp].include?(column.type)
           end
 
-        private
-          def create_time_zone_conversion_attribute?(name, column)
-            time_zone_aware_attributes && !skip_time_zone_conversion_for_attributes.include?(name.to_sym) && [:datetime, :timestamp].include?(column.type)
-          end
       end
     end
   end
diff --git a/activerecord/lib/active_record/attribute_methods/write.rb b/activerecord/lib/active_record/attribute_methods/write.rb
index e31acac050..37eadbe0a9 100644
--- a/activerecord/lib/active_record/attribute_methods/write.rb
+++ b/activerecord/lib/active_record/attribute_methods/write.rb
@@ -17,14 +17,9 @@ module ActiveRecord
       # Updates the attribute identified by <tt>attr_name</tt> with the specified +value+. Empty strings for fixnum and float
       # columns are turned into +nil+.
       def write_attribute(attr_name, value)
-        attr_name = attr_name.to_s
-        attr_name = self.class.primary_key if attr_name == 'id'
+        attr_name = _attributes.unalias(attr_name)
         @attributes_cache.delete(attr_name)
-        if (column = column_for_attribute(attr_name)) && column.number?
-          @attributes[attr_name] = convert_number_column_value(value)
-        else
-          @attributes[attr_name] = value
-        end
+        _attributes[attr_name] = value
       end
 
       private
diff --git a/activerecord/lib/active_record/attributes.rb b/activerecord/lib/active_record/attributes.rb
new file mode 100644
index 0000000000..e4d9e89821
--- /dev/null
+++ b/activerecord/lib/active_record/attributes.rb
@@ -0,0 +1,37 @@
+module ActiveRecord
+  module Attributes
+
+     # Returns true if the given attribute is in the attributes hash
+     def has_attribute?(attr_name)
+       _attributes.key?(attr_name)
+     end
+
+     # Returns an array of names for the attributes available on this object sorted alphabetically.
+     def attribute_names
+       _attributes.keys.sort!
+     end
+
+     # Returns a hash of all the attributes with their names as keys and the values of the attributes as values.
+     def attributes
+       attributes = _attributes.dup
+       attributes.typecast! unless _attributes.frozen?
+       attributes.to_h
+     end
+
+     protected
+
+     # Not to be confused with the public #attributes method, which returns a typecasted Hash.
+     def _attributes
+       @attributes
+     end
+
+     def initialize_attribute_store(merge_attributes = nil)
+       @attributes = ActiveRecord::Attributes::Store.new
+       @attributes.merge!(merge_attributes) if merge_attributes
+       @attributes.types.merge!(self.class.attribute_types)
+       @attributes.aliases.merge!('id' => self.class.primary_key) unless 'id' == self.class.primary_key
+       @attributes
+     end
+
+  end
+end
diff --git a/activerecord/lib/active_record/attributes/aliasing.rb b/activerecord/lib/active_record/attributes/aliasing.rb
new file mode 100644
index 0000000000..db77739d1f
--- /dev/null
+++ b/activerecord/lib/active_record/attributes/aliasing.rb
@@ -0,0 +1,42 @@
+module ActiveRecord
+  module Attributes
+    module Aliasing
+      # Allows access to keys using aliased names.
+      #
+      # Example:
+      # class Attributes < Hash
+      #   include Aliasing
+      # end
+      #
+      # attributes = Attributes.new
+      # attributes.aliases['id'] = 'fancy_primary_key'
+      # attributes['fancy_primary_key'] = 2020
+      #
+      # attributes['id']
+      # => 2020
+      #
+      # Additionally, symbols are always aliases of strings:
+      # attributes[:fancy_primary_key]
+      # => 2020
+      #
+      def [](key)
+        super(unalias(key))
+      end
+
+      def []=(key, value)
+        super(unalias(key), value)
+      end
+
+      def aliases
+        @aliases ||= {}
+      end
+
+      def unalias(key)
+        key = key.to_s
+        aliases[key] || key
+      end
+
+    end
+  end
+end
+
diff --git a/activerecord/lib/active_record/attributes/store.rb b/activerecord/lib/active_record/attributes/store.rb
new file mode 100644
index 0000000000..61109f4acc
--- /dev/null
+++ b/activerecord/lib/active_record/attributes/store.rb
@@ -0,0 +1,15 @@
+module ActiveRecord
+  module Attributes
+    class Store < Hash
+      include ActiveRecord::Attributes::Typecasting
+      include ActiveRecord::Attributes::Aliasing
+
+      # Attributes not mapped to a column are handled using Type::Unknown,
+      # which enables boolean typecasting for unmapped keys.
+      def types
+        @types ||= Hash.new(Type::Unknown.new)
+      end
+
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/attributes/typecasting.rb b/activerecord/lib/active_record/attributes/typecasting.rb
new file mode 100644
index 0000000000..de36a297eb
--- /dev/null
+++ b/activerecord/lib/active_record/attributes/typecasting.rb
@@ -0,0 +1,111 @@
+module ActiveRecord
+  module Attributes
+    module Typecasting
+      # Typecasts values during access based on their key mapping to a Type.
+      #
+      # Example:
+      # class Attributes < Hash
+      #   include Typecasting
+      # end
+      #
+      # attributes = Attributes.new
+      # attributes.types['comments_count'] = Type::Integer
+      # attributes['comments_count'] = '5'
+      #
+      # attributes['comments_count']
+      # => 5
+      #
+      # To support keys not mapped to a typecaster, add a default to types.
+      # attributes.types.default = Type::Unknown
+      # attributes['age'] = '25'
+      # attributes['age']
+      # => '25'
+      #
+      # A valid type supports #cast, #precast, #boolean, and #appendable? methods.
+      #
+      def [](key)
+        value = super(key)
+        typecast_read(key, value)
+      end
+
+      def []=(key, value)
+        super(key, typecast_write(key, value))
+      end
+
+      def to_h
+        hash = {}
+        hash.merge!(self)
+        hash
+      end
+
+      # Provides a duplicate with typecasting disabled.
+      #
+      # Example:
+      # attributes = Attributes.new
+      # attributes.types['comments_count'] = Type::Integer
+      # attributes['comments_count'] = '5'
+      #
+      # attributes.without_typecast['comments_count']
+      # => '5'
+      #
+      def without_typecast
+        dup.without_typecast!
+      end
+
+      def without_typecast!
+        types.clear
+        self
+      end
+
+      def typecast!
+        keys.each { |key| self[key] = self[key] }
+        self
+      end
+
+      # Check if key has a value that typecasts to true.
+      #
+      # attributes = Attributes.new
+      # attributes.types['comments_count'] = Type::Integer
+      #
+      # attributes['comments_count'] = 0
+      # attributes.has?('comments_count')
+      # => false
+      #
+      # attributes['comments_count'] = 1
+      # attributes.has?('comments_count')
+      # => true
+      #
+      def has?(key)
+        value = self[key]
+        boolean_typecast(key, value)
+      end
+
+      def types
+        @types ||= {}
+      end
+
+      protected
+
+      def types=(other_types)
+        @types = other_types
+      end
+
+      def boolean_typecast(key, value)
+        value ? types[key].boolean(value) : false
+      end
+
+      def typecast_read(key, value)
+        type  = types[key]
+        value = type.cast(value)
+        self[key] = value if type.appendable? && !frozen?
+
+        value
+      end
+
+      def typecast_write(key, value)
+        types[key].precast(value)
+      end
+
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index 76dbd00ad9..4274df54cc 100755
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -1644,7 +1644,7 @@ module ActiveRecord #:nodoc:
         def instantiate(record)
           object = find_sti_class(record[inheritance_column]).allocate
 
-          object.instance_variable_set(:'@attributes', record)
+          object.send(:initialize_attribute_store, record)
           object.instance_variable_set(:'@attributes_cache', {})
 
           object.send(:_run_find_callbacks)
@@ -2415,7 +2415,7 @@ module ActiveRecord #:nodoc:
       # In both instances, valid attribute keys are determined by the column names of the associated table --
       # hence you can't have attributes that aren't part of the table columns.
       def initialize(attributes = nil)
-        @attributes = attributes_from_column_definition
+        initialize_attribute_store(attributes_from_column_definition)
         @attributes_cache = {}
         @new_record = true
         ensure_proper_type
@@ -2441,7 +2441,7 @@ module ActiveRecord #:nodoc:
         callback(:after_initialize) if respond_to_without_attributes?(:after_initialize)
         cloned_attributes = other.clone_attributes(:read_attribute_before_type_cast)
         cloned_attributes.delete(self.class.primary_key)
-        @attributes = cloned_attributes
+        initialize_attribute_store(cloned_attributes)
         clear_aggregation_cache
         @attributes_cache = {}
         @new_record = true
@@ -2667,7 +2667,7 @@ module ActiveRecord #:nodoc:
       def reload(options = nil)
         clear_aggregation_cache
         clear_association_cache
-        @attributes.update(self.class.find(self.id, options).instance_variable_get('@attributes'))
+        _attributes.update(self.class.find(self.id, options).instance_variable_get('@attributes'))
         @attributes_cache = {}
         self
       end
@@ -2764,16 +2764,6 @@ module ActiveRecord #:nodoc:
         !value.blank?
       end
 
-      # Returns true if the given attribute is in the attributes hash
-      def has_attribute?(attr_name)
-        @attributes.has_key?(attr_name.to_s)
-      end
-
-      # Returns an array of names for the attributes available on this object sorted alphabetically.
-      def attribute_names
-        @attributes.keys.sort
-      end
-
       # Returns the column object for the named attribute.
       def column_for_attribute(name)
         self.class.columns_hash[name.to_s]
@@ -2897,18 +2887,6 @@ module ActiveRecord #:nodoc:
         end
       end
 
-      def convert_number_column_value(value)
-        if value == false
-          0
-        elsif value == true
-          1
-        elsif value.is_a?(String) && value.blank?
-          nil
-        else
-          value
-        end
-      end
-
       def remove_attributes_protected_from_mass_assignment(attributes)
         safe_attributes =
           if self.class.accessible_attributes.nil? && self.class.protected_attributes.nil?
@@ -3027,7 +3005,7 @@ module ActiveRecord #:nodoc:
       end
 
       def instantiate_time_object(name, values)
-        if self.class.send(:create_time_zone_conversion_attribute?, name, column_for_attribute(name))
+        if self.class.send(:time_zone_aware?, name)
           Time.zone.local(*values)
         else
           Time.time_with_datetime_fallback(@@default_timezone, *values)
@@ -3114,10 +3092,6 @@ module ActiveRecord #:nodoc:
         comma_pair_list(quote_columns(quoter, hash))
       end
 
-      def object_from_yaml(string)
-        return string unless string.is_a?(String) && string =~ /^---/
-        YAML::load(string) rescue string
-      end
   end
 
   Base.class_eval do
@@ -3132,6 +3106,7 @@ module ActiveRecord #:nodoc:
     include AttributeMethods::PrimaryKey
     include AttributeMethods::TimeZoneConversion
     include AttributeMethods::Dirty
+    include Attributes, Types
     include Callbacks, ActiveModel::Observing, Timestamp
     include Associations, AssociationPreload, NamedScope
     include ActiveModel::Conversion
@@ -3141,6 +3116,7 @@ module ActiveRecord #:nodoc:
     include AutosaveAssociation, NestedAttributes
 
     include Aggregations, Transactions, Reflection, Batches, Calculations, Serialization
+
   end
 end
 
diff --git a/activerecord/lib/active_record/types.rb b/activerecord/lib/active_record/types.rb
new file mode 100644
index 0000000000..74f569352b
--- /dev/null
+++ b/activerecord/lib/active_record/types.rb
@@ -0,0 +1,38 @@
+module ActiveRecord
+  module Types
+    extend ActiveSupport::Concern
+
+    module ClassMethods
+
+      def attribute_types
+        attribute_types = {}
+        columns.each do |column|
+          options = {}
+          options[:time_zone_aware] = time_zone_aware?(column.name)
+          options[:serialize]       = serialized_attributes[column.name]
+
+          attribute_types[column.name] = to_type(column, options)
+        end
+        attribute_types
+      end
+
+      private
+
+      def to_type(column, options = {})
+        type_class = if options[:time_zone_aware]
+          Type::TimeWithZone
+        elsif options[:serialize]
+          Type::Serialize
+        elsif [ :integer, :float, :decimal ].include?(column.type)
+          Type::Number
+        else
+          Type::Object
+        end
+
+        type_class.new(column, options)
+      end
+
+    end
+
+  end
+end
diff --git a/activerecord/lib/active_record/types/number.rb b/activerecord/lib/active_record/types/number.rb
new file mode 100644
index 0000000000..cfbe877575
--- /dev/null
+++ b/activerecord/lib/active_record/types/number.rb
@@ -0,0 +1,30 @@
+module ActiveRecord
+  module Type
+    class Number < Object
+
+      def boolean(value)
+        value = cast(value)
+        !(value.nil? || value.zero?)
+      end
+
+      def precast(value)
+        convert_number_column_value(value)
+      end
+
+      private
+
+      def convert_number_column_value(value)
+        if value == false
+          0
+        elsif value == true
+          1
+        elsif value.is_a?(String) && value.blank?
+          nil
+        else
+          value
+        end
+      end
+
+    end
+  end
+end
\ No newline at end of file
diff --git a/activerecord/lib/active_record/types/object.rb b/activerecord/lib/active_record/types/object.rb
new file mode 100644
index 0000000000..ec3f861abd
--- /dev/null
+++ b/activerecord/lib/active_record/types/object.rb
@@ -0,0 +1,37 @@
+module ActiveRecord
+  module Type
+    module Casting
+
+       def cast(value)
+         typecaster.type_cast(value)
+       end
+
+       def precast(value)
+         value
+       end
+
+       def boolean(value)
+         cast(value).present?
+       end
+
+       # Attributes::Typecasting stores appendable? types (e.g. serialized Arrays) when typecasting reads.
+       def appendable?
+         false
+       end
+
+    end
+
+    class Object
+      include Casting
+
+      attr_reader :name, :options
+      attr_reader :typecaster
+
+      def initialize(typecaster = nil, options = {})
+        @typecaster, @options = typecaster, options
+      end
+
+    end
+
+  end
+end
\ No newline at end of file
diff --git a/activerecord/lib/active_record/types/serialize.rb b/activerecord/lib/active_record/types/serialize.rb
new file mode 100644
index 0000000000..7b6af1981f
--- /dev/null
+++ b/activerecord/lib/active_record/types/serialize.rb
@@ -0,0 +1,33 @@
+module ActiveRecord
+  module Type
+    class Serialize < Object
+
+      def cast(value)
+        unserialize(value)
+      end
+
+      def appendable?
+        true
+      end
+
+      protected
+
+      def unserialize(value)
+        unserialized_object = object_from_yaml(value)
+
+        if unserialized_object.is_a?(@options[:serialize]) || unserialized_object.nil?
+          unserialized_object
+        else
+          raise SerializationTypeMismatch,
+            "#{name} was supposed to be a #{@options[:serialize]}, but was a #{unserialized_object.class.to_s}"
+        end
+      end
+
+      def object_from_yaml(string)
+        return string unless string.is_a?(String) && string =~ /^---/
+        YAML::load(string) rescue string
+      end
+
+    end
+  end
+end
\ No newline at end of file
diff --git a/activerecord/lib/active_record/types/time_with_zone.rb b/activerecord/lib/active_record/types/time_with_zone.rb
new file mode 100644
index 0000000000..3a8b9292f9
--- /dev/null
+++ b/activerecord/lib/active_record/types/time_with_zone.rb
@@ -0,0 +1,20 @@
+module ActiveRecord
+  module Type
+    class TimeWithZone < Object
+
+      def cast(time)
+        time = super(time)
+        time.acts_like?(:time) ? time.in_time_zone : time
+      end
+
+      def precast(time)
+        unless time.acts_like?(:time)
+          time = time.is_a?(String) ? ::Time.zone.parse(time) : time.to_time rescue time
+        end
+        time = time.in_time_zone rescue nil if time
+        super(time)
+      end
+
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/types/unknown.rb b/activerecord/lib/active_record/types/unknown.rb
new file mode 100644
index 0000000000..f832c7b304
--- /dev/null
+++ b/activerecord/lib/active_record/types/unknown.rb
@@ -0,0 +1,37 @@
+module ActiveRecord
+  module Type
+    # Useful for handling attributes not mapped to types. Performs some boolean typecasting,
+    # but otherwise leaves the value untouched.
+    class Unknown
+
+      def cast(value)
+        value
+      end
+
+      def precast(value)
+        value
+      end
+
+      # Attempts typecasting to handle numeric, false and blank values.
+      def boolean(value)
+        empty = (numeric?(value) && value.to_i.zero?) || false?(value) || value.blank?
+        !empty
+      end
+
+      def appendable?
+        false
+      end
+
+      protected
+
+      def false?(value)
+        ActiveRecord::ConnectionAdapters::Column::FALSE_VALUES.include?(value)
+      end
+
+      def numeric?(value)
+        Numeric === value || value !~ /[^0-9]/
+      end
+
+    end
+  end
+end
\ No newline at end of file