Adds #key and #to_param to the AMo interface

This commit introduces two new methods that every
AMo compliant object must implement. Below are the
default implementations along with the implied
interface contract.

  # Returns an Enumerable of all (primary) key
  # attributes or nil if new_record? is true
  def key
    new_record? ? nil : [1]
  end

  # Returns a string representing the object's key
  # suitable for use in URLs, or nil if new_record?
  # is true
  def to_param
    key ? key.first.to_s : nil
  end

1) The #key method

Previously rails' record_identifier code, which is
used in the #dom_id helper, relied on calling #id
on the record to provide a reasonable DOM id. Now
with rails3 being all ORM agnostic, it's not safe
anymore to assume that every record ever will have
an #id as its primary key attribute.

Having a #key method available on every AMo object
means that #dom_id can be implemented using

  record.to_model.key # instead of
  record.id

Using this we're able to take composite primary
keys into account (e.g. available in datamapper)
by implementing #dom_id using a newly added

  record_key_for_dom_id(record)

method. The user can overwrite this method to
provide customized versions of the object's key
used in #dom_id.

Also, dealing with more complex keys that can
contain arbitrary strings, means that we need to
make sure that we only provide DOM ids that are
valid according to the spec. For this reason, this
patch sends the key provided through a newly added

  sanitize_dom_id(candidate_id)

method, that makes sure we only produce valid HTML

The reason to not just add #dom_id to the AMo
interface was that it feels like providing a DOM
id should not be a model concern. Adding #dom_id
to the AMo interface would force these concern on
the model, while it's better left to be implemented
in a helper.

Now one could say the same is true for #to_param,
and actually I think that it doesn't really fit
into the model either, but it's used in AR and it's
a main part of integrating into the rails router.

This is different from #dom_id which is only used
in view helpers and can be implemented on top of a
semantically more meaningful method like #key.

2) The #to_param method

Since the rails router relies on #to_param to be
present, AR::Base implements it and returns the
id by default, allowing the user to overwrite the
method if desired.

Now with different ORMs integrating into rails,
every ORM railtie needs to implement it's own
#to_param implementation while already providing
code to be AMo compliant. Since the whole point of
AMo compliance seems to be to integrate any ORM
seamlessly into rails, it seems fair that all we
really need to do as another ORM, is to be AMo
compliant. By including #to_param into the official
interface, we can make sure that this code can be
centralized in the various AMo compliance layers,
and not be added separately by every ORM railtie.

3) All specs pass

8 files changed, 94 insertions, 2 deletions

diff --git a/actionpack/lib/action_controller/record_identifier.rb b/actionpack/lib/action_controller/record_identifier.rb
index 1165c3b7c5..9c35c5b0c3 100644
--- a/actionpack/lib/action_controller/record_identifier.rb
+++ b/actionpack/lib/action_controller/record_identifier.rb
@@ -60,13 +60,32 @@ module ActionController
     #
     #   dom_id(Post.find(45), :edit) # => "edit_post_45"
     def dom_id(record, prefix = nil) 
-      if record_id = record.id
+      if record_id = record_key_for_dom_id(record)
         "#{dom_class(record, prefix)}#{JOIN}#{record_id}"
       else
         dom_class(record, prefix || NEW)
       end
     end
 
+    # Returns a string representation of the key attribute(s) that is suitable for use in an HTML DOM id.
+    # This can be overwritten to customize the default generated string representation if desired.
+    # If you need to read back a key from a dom_id in order to query for the underlying database record,
+    # you should write a helper like 'person_record_from_dom_id' that will extract the key either based
+    # on the default implementation (which just joins all key attributes with '-') or on your own
+    # overwritten version of the method. By default, this implementation passes the key string through a
+    # method that replaces all characters that are invalid inside DOM ids, with valid ones. You need to
+    # make sure yourself that your dom ids are valid, in case you overwrite this method.
+    def record_key_for_dom_id(record)
+      return record.id unless record.respond_to?(:to_model)
+      key = record.to_model.key
+      key ? sanitize_dom_id(key.join('-')) : key
+    end
+
+    # Replaces characters that are invalid in HTML DOM ids with valid ones.
+    def sanitize_dom_id(candidate_id)
+      candidate_id # TODO implement conversion to valid DOM id values
+    end
+
     # Returns the plural class name of a record or class. Examples:
     #
     #   plural_class_name(post)             # => "posts"
diff --git a/actionpack/test/lib/controller/fake_models.rb b/actionpack/test/lib/controller/fake_models.rb
index a8c86f70b6..e4aed14dc0 100644
--- a/actionpack/test/lib/controller/fake_models.rb
+++ b/actionpack/test/lib/controller/fake_models.rb
@@ -6,6 +6,10 @@ class Customer < Struct.new(:name, :id)
 
   undef_method :to_json
 
+  def key
+    id ? [id] : nil
+  end
+
   def to_param
     id.to_s
   end
@@ -43,6 +47,10 @@ module Quiz
     extend ActiveModel::Naming
     include ActiveModel::Conversion
 
+    def key
+      id ? [id] : nil
+    end
+
     def to_param
       id.to_s
     end
@@ -59,6 +67,10 @@ class Post < Struct.new(:title, :author_name, :body, :secret, :written_on, :cost
 
   alias_method :secret?, :secret
 
+  def key
+    id ? [id] : nil
+  end
+
   def new_record=(boolean)
     @new_record = boolean
   end
@@ -84,6 +96,7 @@ class Comment
   attr_reader :id
   attr_reader :post_id
   def initialize(id = nil, post_id = nil); @id, @post_id = id, post_id end
+  def key; id ? [id] : nil end
   def save; @id = 1; @post_id = 1 end
   def new_record?; @id.nil? end
   def to_param; @id; end
@@ -103,6 +116,7 @@ class Tag
   attr_reader :id
   attr_reader :post_id
   def initialize(id = nil, post_id = nil); @id, @post_id = id, post_id end
+  def key; id ? [id] : nil end
   def save; @id = 1; @post_id = 1 end
   def new_record?; @id.nil? end
   def to_param; @id; end
@@ -122,6 +136,7 @@ class CommentRelevance
   attr_reader :id
   attr_reader :comment_id
   def initialize(id = nil, comment_id = nil); @id, @comment_id = id, comment_id end
+  def key; id ? [id] : nil end
   def save; @id = 1; @comment_id = 1 end
   def new_record?; @id.nil? end
   def to_param; @id; end
@@ -137,6 +152,7 @@ class TagRelevance
   attr_reader :id
   attr_reader :tag_id
   def initialize(id = nil, tag_id = nil); @id, @tag_id = id, tag_id end
+  def key; id ? [id] : nil end
   def save; @id = 1; @tag_id = 1 end
   def new_record?; @id.nil? end
   def to_param; @id; end
diff --git a/actionpack/test/template/prototype_helper_test.rb b/actionpack/test/template/prototype_helper_test.rb
index d95bdc2b90..dab34f1201 100644
--- a/actionpack/test/template/prototype_helper_test.rb
+++ b/actionpack/test/template/prototype_helper_test.rb
@@ -4,6 +4,7 @@ require 'active_model'
 class Bunny < Struct.new(:Bunny, :id)
   extend ActiveModel::Naming
   include ActiveModel::Conversion
+  def key() id ? [id] : nil end
 end
 
 class Author
@@ -11,6 +12,7 @@ class Author
   include ActiveModel::Conversion
 
   attr_reader :id
+  def key() id ? [id] : nil end
   def save; @id = 1 end
   def new_record?; @id.nil? end
   def name
@@ -23,6 +25,7 @@ class Article
   include ActiveModel::Conversion
   attr_reader :id
   attr_reader :author_id
+  def key() id ? [id] : nil end
   def save; @id = 1; @author_id = 1 end
   def new_record?; @id.nil? end
   def name
diff --git a/activemodel/lib/active_model/lint.rb b/activemodel/lib/active_model/lint.rb
index 7bf0ad712d..c97286e61c 100644
--- a/activemodel/lib/active_model/lint.rb
+++ b/activemodel/lib/active_model/lint.rb
@@ -13,6 +13,29 @@
 module ActiveModel
   module Lint
     module Tests
+
+      # == Responds to <tt>key</tt>
+      #
+      # Returns an Enumerable of all (primary) key attributes
+      # or nil if model.new_record? is true
+      def test_key
+        assert model.respond_to?(:key), "The model should respond to key"
+        def model.new_record?() true end
+        assert model.key.nil?
+        def model.new_record?() false end
+        assert model.key.respond_to?(:each)
+      end
+
+      # == Responds to <tt>to_param</tt>
+      #
+      # Returns a string representing the object's key suitable for use in URLs
+      # or nil if model.new_record? is true
+      def test_to_param
+        assert model.respond_to?(:to_param), "The model should respond to to_param"
+        def model.new_record?() true end
+        assert model.to_param.nil?
+      end
+
       # == Responds to <tt>valid?</tt>
       #
       # Returns a boolean that specifies whether the object is in a valid or invalid
diff --git a/activemodel/lib/active_model/naming.rb b/activemodel/lib/active_model/naming.rb
index 89e8f8b1ea..39512a427b 100644
--- a/activemodel/lib/active_model/naming.rb
+++ b/activemodel/lib/active_model/naming.rb
@@ -41,7 +41,7 @@ module ActiveModel
   # To implement, just extend ActiveModel::Naming in your object:
   # 
   #   class BookCover
-  #     exten ActiveModel::Naming
+  #     extend ActiveModel::Naming
   #   end
   # 
   #   BookCover.model_name        #=> "BookCover"
diff --git a/activemodel/test/cases/lint_test.rb b/activemodel/test/cases/lint_test.rb
index 63804004ee..58716cbf85 100644
--- a/activemodel/test/cases/lint_test.rb
+++ b/activemodel/test/cases/lint_test.rb
@@ -10,6 +10,14 @@ class LintTest < ActiveModel::TestCase
       self
     end
 
+    def key
+      new_record? ? nil : [1]
+    end
+
+    def to_param
+      key ? key.first.to_s : nil
+    end
+
     def valid?()      true end
     def new_record?() true end
     def destroyed?()  true end
diff --git a/activerecord/lib/active_record/attribute_methods/primary_key.rb b/activerecord/lib/active_record/attribute_methods/primary_key.rb
index 365fdeb55a..ba64b8ee2f 100644
--- a/activerecord/lib/active_record/attribute_methods/primary_key.rb
+++ b/activerecord/lib/active_record/attribute_methods/primary_key.rb
@@ -39,6 +39,20 @@ module ActiveRecord
         end
         alias :primary_key= :set_primary_key
       end
+
+      module InstanceMethods
+
+        # Returns this record's primary key value wrapped in an Array
+        # or nil if the record is a new_record?
+        # This is done to comply with the AMo interface that expects
+        # every AMo compliant object to respond_to?(:key) and return
+        # an Enumerable object from that call, or nil if new_record?
+        def key
+          new_record? ? nil : [ self.id ]
+        end
+
+      end
+
     end
   end
 end
diff --git a/activerecord/test/cases/pk_test.rb b/activerecord/test/cases/pk_test.rb
index c121e0aa0f..2502c136cc 100644
--- a/activerecord/test/cases/pk_test.rb
+++ b/activerecord/test/cases/pk_test.rb
@@ -9,6 +9,15 @@ require 'models/mixed_case_monkey'
 class PrimaryKeysTest < ActiveRecord::TestCase
   fixtures :topics, :subscribers, :movies, :mixed_case_monkeys
 
+  def test_key
+    # test new record
+    topic = Topic.new
+    assert topic.key.nil?
+    # test existing record
+    topic = Topic.find(1)
+    assert_equal topic.key, [1]
+  end
+
   def test_integer_key
     topic = Topic.find(1)
     assert_equal(topics(:first).author_name, topic.author_name)