# How to change one attribute (or a group of attributes) when another changes? **URL:** \ **Category:** Rails\ **Created:** [May 17, 2010, 9:24am UTC](https://www.ruby-forum.com/t/how-to-change-one-attribute-or-a-group-of-attributes-when-another-changes/188719 "2010-05-17T09:24:05Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![chewmanfoo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/c37758/32.png) [@chewmanfoo](https://www.ruby-forum.com/u/chewmanfoo)\ **Post date:** [May 17, 2010, 9:24am UTC](https://www.ruby-forum.com/t/how-to-change-one-attribute-or-a-group-of-attributes-when-another-changes/188719/1 "2010-05-17T09:24:05Z")
I have a hosts class with an ip\_addresses class which has a host\_id attribute. All hosts are associated with a data\_center, and all ip\_addresses are associated with a network. Networks have a standard IP network definition (192.168.59.0/24) etc. When a user changes that network definition, I need to go through all ip\_addresses in the network and change them to agree with the new network definition. For example, if the network is defined as 192.168.59.0/24, and the user changes it to 10.168.59.0/24 in the networks form, I need to change all the ip\_addresses in that network to match the new scheme. So I need to know when the network changes. How do I do this? Like, is there a way to add code to the function that sets the network definition? ---
**Author:** ![chewmanfoo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/c37758/32.png) [@chewmanfoo](https://www.ruby-forum.com/u/chewmanfoo)\ **Post date:** [May 17, 2010, 6:33pm UTC](https://www.ruby-forum.com/t/how-to-change-one-attribute-or-a-group-of-attributes-when-another-changes/188719/2 "2010-05-17T18:33:47Z")
On May 16, 2010, at 6:20 PM, chewmanfoo wrote: > there a way to add code to the function that sets the network > definition? Add an ‘after\_save’ method to your Network model that checks to see what’s changed and if appropriate goes through and changes all of it’s IP\_Address children… -philip ---
**Author:** ![chewmanfoo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/c37758/32.png) [@chewmanfoo](https://www.ruby-forum.com/u/chewmanfoo)\ **Post date:** [May 17, 2010, 11:21pm UTC](https://www.ruby-forum.com/t/how-to-change-one-attribute-or-a-group-of-attributes-when-another-changes/188719/3 "2010-05-17T23:21:47Z")
On 17 May 2010 02:20, chewmanfoo [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > there a way to add code to the function that sets the network > definition? I think you have redundant data in the db, as you are storing the ip address and the network definition, where much of the data is common between these two. I suggest not storing the full ip address, just the offset from that in the network definition, or something similar. Then your problem will go away. Colin ---
**Author:** ![chewmanfoo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/c37758/32.png) [@chewmanfoo](https://www.ruby-forum.com/u/chewmanfoo)\ **Post date:** [May 17, 2010, 11:30pm UTC](https://www.ruby-forum.com/t/how-to-change-one-attribute-or-a-group-of-attributes-when-another-changes/188719/4 "2010-05-17T23:30:34Z")
Colin, You’re right! But I can’t go down that path right now. In the future I’ll refactor the heck out of tis rats nest, but for now I have to make it work. Jason ---
**Author:** ![chewmanfoo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/c37758/32.png) [@chewmanfoo](https://www.ruby-forum.com/u/chewmanfoo)\ **Post date:** [May 18, 2010, 1:31am UTC](https://www.ruby-forum.com/t/how-to-change-one-attribute-or-a-group-of-attributes-when-another-changes/188719/5 "2010-05-18T01:31:31Z")
Jason M. wrote: > Colin, > > You’re right! But I can’t go down that path right now. In the future > I’ll > refactor the heck out of tis rats nest, but for now I have to make it > work. > > Jason If it’s a “rats nest”, it will probably be faster to refactor than to try to maintain it as it is. ## Best, Marnen Laibow-Koser [http://www.marnen.org](http://www.marnen.org) removed\_email\_address@domain.invalid