improving support assignment model validations

app/models/support_assignment.rb

@@ -1,4 +1,7 @@
 class SupportAssignment < ActiveRecord::Base
   belongs_to :user
-  validates :user_id, uniqueness: {:scope => :date}
+  validates :user_id, uniqueness: {:scope => :date, message: "already to duty on this date"}
+  validate do | assignment |
+    assignment.errors.add(:user_id, ' is unavailable on the specified date') unless assignment.user.available?(assignment.date)
+  end
 end

app/models/user.rb

@@ -18,6 +18,10 @@ def future_assignment
     support_assignments.select{ |assignment| assignment.date.future? }.first
   end
 
+  def self.available_users date
+    User.where(unavailable_date: nil) | User.where.not(unavailable_date: date)
+  end
+
   private
 
   def reconcile_schedule_conflicts date
@@ -35,7 +39,5 @@ def replace_assignment assignment
     future_assignment.destroy
   end
 
-  def available_users date
-    User.where(unavailable_date: nil) | User.where.not(unavailable_date: date)
-  end
+
 end

app/views/support_assignments/_form.html.erb

@@ -17,7 +17,7 @@
   </div>
   <div class="field">
     <%= f.label :user_id %><br>
-    <%= f.collection_select(:user_id, Schedule.new.available_users(@support_assignment.date), :id, :name)  %>
+    <%= f.collection_select(:user_id, User.available_users(@support_assignment.date), :id, :name)  %>
   </div>
   <div class="actions">
     <%= f.submit %>