Integrate with Active Model Attributes

The `schema { ... }` interface pre-dates the Active Model Attributes API
(defined as early as [v5.2.0][]), but clearly draws inspiration from
Active Record's Database Schema and Attribute casting (which was
extracted into `ActiveModel::Attributes`).

However, the type information captured in `schema { ... }` blocks or
assigned as `Hash` arguments to `schema=` is purely inert metadata.

Proposal
---

This commit aims to integrate with [ActiveModel::Model][] and
[ActiveModel::Attributes][]. Through the introduction of both modules,
subclasses of `ActiveResource::Schema` can benefit from type casting
attributes and constructing instances with default values.

This commit makes minimally incremental changes, prioritizing backwards
compatibility. The reliance on `#respond_to_missing?` and
`#method_missing` is left largely unchanged. Similarly, the `Schema`
interface continues to provide metadata about its attributes through the
`Schema#attr` method (instead of reading from
`ActiveModel::Attributes#attribute_names` or
`ActiveModel::Attributes.attribute_types`).

API Changes
---

To cast values to their specified types, declare the Schema with the
`:cast_values` set to true.

```ruby
class Person < ActiveResource::Base
  schema cast_values: true do
    integer 'age'
  end
end

p = Person.new
p.age = "18"
p.age # => 18
```

To configure inheriting resources to cast values, set the `cast_values`
class attribute:

```ruby
class ApplicationResource < ActiveResource::Base
  self.cast_values = true
end

class Person < ApplicationResource
  schema do
    integer 'age'
  end
end

p = Person.new
p.age = "18"
p.age # => 18
```

To set all resources application-wide to cast values, set
`config.active_resource.cast_values`:

```ruby
  # config/application.rb
  config.active_resource.cast_values = true
```

[v5.2.0]: https://api.rubyonrails.org/v5.2.0/classes/ActiveModel/Attributes/ClassMethods.html
[ActiveModel::Model]: https://api.rubyonrails.org/classes/ActiveModel/Model.html
[ActiveModel::Attributes]: https://api.rubyonrails.org/classes/ActiveModel/Attributes/ClassMethods.html

lib/active_resource/base.rb

@@ -335,6 +335,12 @@ def self.logger=(logger)
     class_attribute :connection_class
     self.connection_class = Connection
 
+    class_attribute :cast_values, instance_accessor: false, instance_predicate: false # :nodoc:
+    self.cast_values = false
+
+    class_attribute :schema_definition, instance_accessor: false, instance_predicate: false # :nodoc:
+    self.schema_definition = Schema
+
     class << self
       include ThreadsafeAttributes
       threadsafe_attribute :_headers, :_connection, :_user, :_password, :_bearer_token, :_site, :_proxy
@@ -385,16 +391,49 @@ class << self
       #
       # Attribute-types must be one of: <tt>string, text, integer, float, decimal, datetime, timestamp, time, date, binary, boolean</tt>
       #
-      # Note: at present the attribute-type doesn't do anything, but stay
-      # tuned...
-      # Shortly it will also *cast* the value of the returned attribute.
-      # ie:
-      # j.age                 # => 34   # cast to an integer
-      # j.weight              # => '65' # still a string!
+      # Note: By default, the attribute-type is ignored and will not cast its
+      # value.
+      #
+      # To cast values to their specified types, declare the Schema with the
+      # +:cast_values+ set to true.
+      #
+      #   class Person < ActiveResource::Base
+      #     schema cast_values: true do
+      #       integer 'age'
+      #     end
+      #   end
+      #
+      #   p = Person.new
+      #   p.age = "18"
+      #   p.age # => 18
+      #
+      # To configure inheriting resources to cast values, set the +cast_values+
+      # class attribute:
+      #
+      #   class ApplicationResource < ActiveResource::Base
+      #     self.cast_values = true
+      #   end
+      #
+      #   class Person < ApplicationResource
+      #     schema do
+      #       integer 'age'
+      #     end
+      #   end
+      #
+      #   p = Person.new
+      #   p.age = "18"
+      #   p.age # => 18
+      #
+      # To set all resources application-wide to cast values, set
+      # +config.active_resource.cast_values+:
+      #
+      #   # config/application.rb
+      #   config.active_resource.cast_values = true
       #
-      def schema(&block)
+      def schema(cast_values: self.cast_values, &block)
         if block_given?
-          schema_definition = Schema.new
+          self.schema_definition = Class.new(Schema)
+          schema_definition.cast_values = cast_values
           schema_definition.instance_eval(&block)
 
           # skip out if we didn't define anything
@@ -434,6 +473,7 @@ def schema(&block)
       def schema=(the_schema)
         unless the_schema.present?
           # purposefully nulling out the schema
+          self.schema_definition = Schema
           @schema = nil
           @known_attributes = []
           return
@@ -1213,6 +1253,7 @@ def known_attributes
     def initialize(attributes = {}, persisted = false)
       @attributes     = {}.with_indifferent_access
       @prefix_options = {}
+      @schema         = self.class.schema_definition.new
       @persisted = persisted
       load(attributes, false, persisted)
     end
@@ -1246,6 +1287,7 @@ def clone
       resource = self.class.new({})
       resource.prefix_options = self.prefix_options
       resource.send :instance_variable_set, "@attributes", cloned
+      resource.send :instance_variable_set, "@schema", @schema.clone
       resource
     end
 
@@ -1285,12 +1327,12 @@ def persisted?
 
     # Gets the <tt>\id</tt> attribute of the resource.
     def id
-      attributes[self.class.primary_key]
+      _read_attribute(self.class.primary_key)
     end
 
     # Sets the <tt>\id</tt> attribute of the resource.
     def id=(id)
-      attributes[self.class.primary_key] = id
+      _write_attribute(self.class.primary_key, id)
     end
 
     # Test for equality. Resource are equal if and only if +other+ is the same object or
@@ -1481,7 +1523,7 @@ def load(attributes, remove_root = false, persisted = false)
       attributes = Formats.remove_root(attributes) if remove_root
 
       attributes.each do |key, value|
-        @attributes[key.to_s] =
+        _write_attribute(key,
           case value
           when Array
             resource = nil
@@ -1498,7 +1540,7 @@ def load(attributes, remove_root = false, persisted = false)
             resource.new(value, persisted)
           else
             value.duplicable? ? value.dup : value
-          end
+          end)
       end
       self
     end
@@ -1541,7 +1583,9 @@ def update_attributes(attributes)
     # <tt>my_person.respond_to?(:name?)</tt>.
     def respond_to_missing?(method, include_priv = false)
       method_name = method.to_s
-      if attributes.nil?
+      if @schema.respond_to?(method)
+        true
+      elsif attributes.nil?
         super
       elsif known_attributes.include?(method_name)
         true
@@ -1698,10 +1742,28 @@ def split_options(options = {})
         self.class.__send__(:split_options, options)
       end
 
+      def _read_attribute(name)
+        if @schema.respond_to?(name)
+          @schema.send(name)
+        else
+          attributes[name.to_s]
+        end
+      end
+
+      def _write_attribute(name, value)
+        if @schema.respond_to?("#{name}=")
+          @schema.send("#{name}=", value)
+        else
+          attributes[name.to_s] = value
+        end
+      end
+
       def method_missing(method_symbol, *arguments) # :nodoc:
         method_name = method_symbol.to_s
 
-        if method_name =~ /(=|\?)$/
+        if @schema.respond_to?(method_name)
+          @schema.send(method_name, *arguments)
+        elsif method_name =~ /(=|\?)$/
           case $1
           when "="
             attributes[$`] = arguments.first

lib/active_resource/schema.rb

@@ -2,14 +2,24 @@
 
 module ActiveResource # :nodoc:
   class Schema # :nodoc:
+    include ActiveModel::Model
+    include ActiveModel::Attributes
+
     # attributes can be known to be one of these types. They are easy to
     # cast to/from.
     KNOWN_ATTRIBUTE_TYPES = %w( string text integer float decimal datetime timestamp time date binary boolean )
 
     # An array of attribute definitions, representing the attributes that
     # have been defined.
-    attr_accessor :attrs
+    class_attribute :attrs, instance_accessor: false, instance_predicate: false # :nodoc:
+    self.attrs = {}
+
+    class_attribute :cast_values, instance_accessor: false, instance_predicate: false # :nodoc:
+    self.cast_values = false
 
+    ##
+    # :method: initialize
+    #
     # The internals of an Active Resource Schema are very simple -
     # unlike an Active Record TableDefinition (on which it is based).
     # It provides a set of convenience methods for people to define their
@@ -22,39 +32,56 @@ class Schema # :nodoc:
     #  The schema stores the name and type of each attribute. That is then
     #  read out by the schema method to populate the schema of the actual
     #  resource.
-    def initialize
-      @attrs = {}
-    end
-
-    def attribute(name, type, options = {})
-      raise ArgumentError, "Unknown Attribute type: #{type.inspect} for key: #{name.inspect}" unless type.nil? || Schema::KNOWN_ATTRIBUTE_TYPES.include?(type.to_s)
 
-      the_type = type.to_s
-      # TODO: add defaults
-      # the_attr = [type.to_s]
-      # the_attr << options[:default] if options.has_key? :default
-      @attrs[name.to_s] = the_type
-      self
-    end
+    class << self
+      def inherited(subclass)
+        super
+        subclass.attrs = attrs.dup
+      end
 
-    # The following are the attribute types supported by Active Resource
-    # migrations.
-    KNOWN_ATTRIBUTE_TYPES.each do |attr_type|
-      # def string(*args)
-      #   options = args.extract_options!
-      #   attr_names = args
+      # The internals of an Active Resource Schema are very simple -
+      # unlike an Active Record TableDefinition (on which it is based).
+      # It provides a set of convenience methods for people to define their
+      # schema using the syntax:
+      #  schema do
+      #    string :foo
+      #    integer :bar
+      #  end
       #
-      #   attr_names.each { |name| attribute(name, 'string', options) }
-      # end
-      class_eval <<-EOV, __FILE__, __LINE__ + 1
-        # frozen_string_literal: true
-        def #{attr_type}(*args)
-          options = args.extract_options!
-          attr_names = args
-
-          attr_names.each { |name| attribute(name, '#{attr_type}', options) }
-        end
-      EOV
+      #  The schema stores the name and type of each attribute. That is then
+      #  read out by the schema method to populate the schema of the actual
+      #  resource.
+      def attribute(name, type, **options)
+        raise ArgumentError, "Unknown Attribute type: #{type.inspect} for key: #{name.inspect}" unless type.nil? || Schema::KNOWN_ATTRIBUTE_TYPES.include?(type.to_s)
+
+        the_type = type.to_s
+        attrs[name.to_s] = the_type
+
+        type = cast_values ? type.to_sym : nil
+
+        super
+        self
+      end
+
+      # The following are the attribute types supported by Active Resource
+      # migrations.
+      KNOWN_ATTRIBUTE_TYPES.each do |attr_type|
+        # def string(*args)
+        #   options = args.extract_options!
+        #   attr_names = args
+        #
+        #   attr_names.each { |name| attribute(name, 'string', options) }
+        # end
+        class_eval <<-EOV, __FILE__, __LINE__ + 1
+          # frozen_string_literal: true
+          def #{attr_type}(*args)
+            options = args.extract_options!
+            attr_names = args
+
+            attr_names.each { |name| attribute(name, :#{attr_type}, **options) }
+          end
+        EOV
+      end
     end
   end
 end

test/cases/base/schema_test.rb

@@ -15,6 +15,7 @@ def setup
 
   def teardown
     Person.schema = nil # hack to stop test bleedthrough...
+    Person.cast_values = false # hack to stop test bleedthrough...
   end
 
 
@@ -425,4 +426,54 @@ def teardown
     Person.schema = new_schema
     assert_equal Person.new(age: 20, name: "Matz").known_attributes, ["age", "name"]
   end
+
+  test "clone with schema that casts values" do
+    Person.cast_values = true
+    Person.schema = { "age" => "integer" }
+    person = Person.new({ Person.primary_key => 1, "age" => "10" }, true)
+
+    person_c = person.clone
+
+    assert_predicate person_c, :new?
+    assert_nil person_c.send(Person.primary_key)
+    assert_equal 10, person_c.age
+  end
+
+  test "known primary_key attributes should be cast" do
+    Person.schema cast_values: true do
+      attribute Person.primary_key, :integer
+    end
+
+    person = Person.new(Person.primary_key => "1")
+
+    assert_equal 1, person.send(Person.primary_key)
+  end
+
+  test "known attributes should be cast" do
+    Person.schema cast_values: true do
+      attribute :born_on, :date
+    end
+
+    person = Person.new(born_on: "2000-01-01")
+
+    assert_equal Date.new(2000, 1, 1), person.born_on
+  end
+
+  test "known attributes should be support default values" do
+    Person.schema cast_values: true do
+      attribute :name, :string, default: "Default Name"
+    end
+
+    person = Person.new
+
+    assert_equal "Default Name", person.name
+  end
+
+  test "unknown attributes should not be cast" do
+    Person.cast_values = true
+
+    person = Person.new(age: "10")
+
+    assert_equal "10", person.age
+  end
 end