3 files changed, 168 insertions, 0 deletions
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