add ability to detach/dissasociate and add new_record? method

lib/fog/aws/models/ec2/address.rb

@@ -21,12 +21,10 @@ module Fog
         end
 
         def instance=(new_instance)
-          if !@public_ip
-            @instance = new_instance
-          elsif new_instance
-            @instance = nil
-            @instance_id = new_instance.instance_id
-            connection.associate_address(@instance_id, @public_ip)
+          if new_instance
+            associate(new_instance)
+          else
+            detach
           end
         end
 
@@ -39,6 +37,26 @@ module Fog
           true
         end
 
+        private
+
+        def associate(new_instance)
+          if new_record?
+            @instance = new_instance
+          else
+            @instance = nil
+            @instance_id = new_instance.instance_id
+            connection.associate_address(@instance_id, @public_ip)
+          end
+        end
+
+        def disassociate
+          @instance = nil
+          @instance_id = nil
+          unless new_record?
+            connection.disassociate_address(@public_ip)
+          end
+        end
+
       end
 
     end

lib/fog/aws/models/ec2/volume.rb

@@ -28,15 +28,10 @@ module Fog
         end
 
         def instance=(new_instance)
-          if !@volume_id
-            @instance = new_instance
-            if new_instance
-              @availability_zone = new_instance.availability_zone
-            end
-          elsif new_instance
-            @instance = nil
-            @instance_id = new_instance.instance_id
-            connection.attach_volume(@instance_id, @volume_id, @device)
+          if new_instance
+            attach(new_instance)
+          else
+            detach
           end
         end
 
@@ -54,6 +49,27 @@ module Fog
           connection.snapshots(:volume_id => volume_id)
         end
 
+        private
+
+        def attach(new_instance)
+          if new_record?
+            @instance = new_instance
+            @availability_zone = new_instance.availability_zone
+          elsif new_instance
+            @instance = nil
+            @instance_id = new_instance.instance_id
+            connection.attach_volume(@instance_id, @volume_id, @device)
+          end
+        end
+
+        def detach
+          @instance = nil
+          @instance_id = nil
+          unless new_record?
+            connection.detach_volume(@volume_id)
+          end
+        end
+
       end
 
     end

lib/fog/model.rb

@@ -63,6 +63,10 @@ module Fog
       self
     end
 
+    def new_record?
+      !identity
+    end
+
     def reload
       new_attributes = collection.get(identity).attributes
       merge_attributes(new_attributes)