fix #1310 [fields marked as required incorrectly based on validators]

lib/rails_admin/config/fields/base.rb

@@ -164,10 +164,12 @@ def virtual?
         #
         # @see RailsAdmin::AbstractModel.properties
         register_instance_option :required? do
-          @required ||= !!([name] + children_fields).uniq.find do |column_name|
+          context = (bindings && bindings[:object].try(:persisted?) ? :update : :create)          
+          (@required ||= {})[context] ||= !!([name] + children_fields).uniq.find do |column_name|
             !!abstract_model.model.validators_on(column_name).find do |v|
-              v.kind == :presence && !v.options[:allow_nil] ||
-              v.kind == :numericality && !v.options[:allow_nil]
+              !v.options[:allow_nil] and
+              [:presence, :numericality].include?(v.kind) and
+              (v.options[:on] == context or v.options[:on].blank?)
             end
           end
         end

spec/dummy_app/app/active_record/ball.rb

@@ -1,7 +1,7 @@
 class Ball < ActiveRecord::Base
   attr_accessible :color
 
-  validates_presence_of :color
+  validates_presence_of :color, :on => :create
 
   def to_param
     color.present? ? color.downcase.gsub(" ", "-") : id

spec/unit/config/fields/base_spec.rb

@@ -2,6 +2,18 @@
 
 describe RailsAdmin::Config::Fields::Base do
 
+  describe "#required" do
+
+    it "should read the :on => :create/:update validate option" do
+      RailsAdmin.config Ball do
+        field 'color'
+      end
+
+      RailsAdmin.config('Ball').fields.first.with(:object => Ball.new).should be_required
+      RailsAdmin.config('Ball').fields.first.with(:object => FactoryGirl.create(:ball)).should_not be_required
+    end
+  end
+
   describe "#name" do
     it 'should be normalized to Symbol' do
       RailsAdmin.config Team do