Should be able to set contextual validations

Contextual validations are active __only__ within
an appropriate context: either ”create" or ”update”.

validates(:name, :presence => true, :on => :create)

validates(:name, :presence => {:on => :update})

See http://edgeguides.rubyonrails.org/active_record_validations_callbacks.html#on

Should fix https://github.com/couchrest/couchrest_model/pull/90

lib/couchrest/model/base.rb

@@ -7,7 +7,6 @@ module CouchRest
       include CouchRest::Model::Configuration
       include CouchRest::Model::Connection
       include CouchRest::Model::Persistence
-      include CouchRest::Model::Callbacks
       include CouchRest::Model::DocumentQueries
       include CouchRest::Model::Views
       include CouchRest::Model::DesignDoc
@@ -21,6 +20,7 @@ module CouchRest
       include CouchRest::Model::Designs
       include CouchRest::Model::CastedBy
       include CouchRest::Model::Dirty
+      include CouchRest::Model::Callbacks
 
       def self.subclasses
         @subclasses ||= []

lib/couchrest/model/callbacks.rb

@@ -16,8 +16,10 @@ module CouchRest #:nodoc:
 
       end
 
-      def valid?(*) #nodoc
-        _run_validation_callbacks { super }
+      def valid?(context = nil)
+        context ||= (new_record? ? :create : :update)
+        output = super(context)
+        errors.empty? && output
       end
 
     end

lib/couchrest/model/casted_model.rb

@@ -5,13 +5,14 @@ module CouchRest::Model
 
     included do
       include CouchRest::Model::Configuration
-      include CouchRest::Model::Callbacks
       include CouchRest::Model::Properties
       include CouchRest::Model::PropertyProtection
       include CouchRest::Model::Associations
       include CouchRest::Model::Validations
       include CouchRest::Model::CastedBy
       include CouchRest::Model::Dirty
+      include CouchRest::Model::Callbacks
+
       class_eval do
         # Override CastedBy's base_doc?
         def base_doc?