Adding uniqueness validation support out of the box

lib/couchrest/model/validations/locale/en.yml

@@ -0,0 +1,5 @@
+en:
+  errors:
+    messages:
+      taken: "is already taken"
+

lib/couchrest/model/validations/uniqueness.rb

@@ -0,0 +1,42 @@
+# encoding: urf-8
+
+module CouchRest
+  module Model
+    module Validations
+      
+      # Validates if a field is unique 
+      class UniquenessValidator < ActiveModel::EachValidator
+
+        # Ensure we have a class available so we can check for a usable view
+        # or add one if necessary.
+        def setup(klass)
+          @klass = klass
+        end
+
+
+        def validate_each(document, attribute, value)
+          unless @klass.has_view?("by_#{attribute}")
+            @klass.view_by attribute
+          end
+
+          # Determine the base of the search
+          base = options[:proxy].nil? ? @klass : document.send(options[:proxy])
+
+          docs = base.view("by_#{attribute}", :key => value, :limit => 2, :include_docs => false)['rows']
+          return if docs.empty?
+
+          unless document.new?
+            return if docs.find{|doc| doc['id'] == document.id}
+          end
+          
+          if docs.length > 0
+            document.errors.add(attribute, :taken, :default => options[:message], :value => value)
+          end
+        end
+
+
+      end
+
+    end
+  end
+end