Support optional types for computed attributes

README.md

@@ -232,6 +232,20 @@ class PostSerializer < ActiveModel::Serializer
 end
 ```
 
+The type of a computed attribute (like :full_name above) is not easily
+calculated without some sophisticated static code analysis. To specify the
+type of a computed attribute:
+
+```ruby
+class PersonSerializer < ActiveModel::Serializer
+  attributes :first_name, :last_name, {:full_name => :string}
+
+  def full_name
+    "#{object.first_name} #{object.last_name}"
+  end
+end
+```
+
 If you would like the key in the outputted JSON to be different from its name
 in ActiveRecord, you can use the `:key` option to customize it:
 

lib/active_model/serializer.rb

@@ -73,7 +73,9 @@ def attributes(*attrs)
       end
 
       def attribute(attr, options={})
-        self._attributes = _attributes.merge(attr => options[:key] || attr.to_s.gsub(/\?$/, '').to_sym)
+        self._attributes = _attributes.merge(attr.is_a?(Hash) ? attr : {attr => options[:key] || attr.to_s.gsub(/\?$/, '').to_sym})
+
+        attr = attr.keys[0] if attr.is_a? Hash
 
         unless method_defined?(attr)
           define_method attr do
@@ -175,8 +177,12 @@ def schema
             attrs[key] = column.type
           else
             # Computed attribute (method on serializer or model). We cannot
-            # infer the type, so we put nil.
-            attrs[key] = nil
+            # infer the type, so we put nil, unless specified in the attribute declaration
+            if name != key
+              attrs[name] = key
+            else
+              attrs[key] = nil
+            end
           end
         end
 

test/serializer_test.rb

@@ -491,16 +491,17 @@ class << self; self; end.class_eval do
 
       # Computed attributes (not real columns or associations).
       def can_edit; end
+      def can_view; end
       def drafts; end
 
-      attributes :name, :age, :can_edit
+      attributes :name, :age, {:can_edit => :boolean}, :can_view
       has_many :posts, :serializer => Class.new
       has_many :drafts, :serializer => Class.new
       has_one :parent, :serializer => Class.new
     end
 
     assert_equal serializer.schema, {
-      :attributes => { :name => :string, :age => :integer, :can_edit => nil },
+      :attributes => { :name => :string, :age => :integer, :can_edit => :boolean, :can_view => nil },
       :associations => {
         :posts => { :has_many => :posts },
         :drafts => nil,
@@ -1004,7 +1005,7 @@ def self.to_s
         :name => 'logo.png',
         :url => 'http://example.com/logo.png',
         :attachable => {
-          :type => :email, 
+          :type => :email,
           :id => 1
         }},
       :emails => [{