# Questions about ActiveRecord aggregation **URL:** \ **Category:** Rails\ **Created:** [April 6, 2007, 12:06pm UTC](https://www.ruby-forum.com/t/questions-about-activerecord-aggregation/91295 "2007-04-06T12:06:07Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![allen](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/bbce88/32.png) [@allen](https://www.ruby-forum.com/u/allen)\ **Post date:** [April 6, 2007, 12:06pm UTC](https://www.ruby-forum.com/t/questions-about-activerecord-aggregation/91295/1 "2007-04-06T12:06:07Z")
Hi all, I’m quite new to rails. These may be silly questions, but I really need your advice. According to \<\>, composite objects in aggregation are value objects, which means their values cannot be changed. So if say Person is the model class and Address is the composite class, the way to update a person’s address is to create a new Address object, assign it to the person and then save. This works fine with small composite object with just a few properties. If the composite object has many properties, I think this will a performance problem. Now in my project, I get a table with about 50-60 columns. I want to divide it into several parts using aggregation. The problem is that, one of these composite objects will have 20 columns and another with 10 columns. I’m wondering if this will cause a performance problem since each time even only one of the composite object’s properties needs to be updated, the whole 20 columns or so will be updated together. Is there a way to avoid this? Or this is just the way rails work? I was thinking about split this big table into several small ones, but this doesn’t seem to be reasonable in a OO perspective. Do I have to split the table in order to hold performance or is there better way? Aonther question is about multi-layer aggregation, say I want to model a table into A, B, C there classes and use a a.b.c relationship. Is this possible? Thanks a lot. ---
**Author:** ![allen](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/bbce88/32.png) [@allen](https://www.ruby-forum.com/u/allen)\ **Post date:** [April 6, 2007, 9:08pm UTC](https://www.ruby-forum.com/t/questions-about-activerecord-aggregation/91295/2 "2007-04-06T21:08:54Z")
allen wrote: > Hi all, > > Aonther question is about multi-layer aggregation, say I want to model > a table into A, B, C there classes and use a a.b.c relationship. Is > this possible? > > Thanks a lot. Yes, Take a look here: > **[ActiveRecord::Associations::ClassMethods](https://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html#M000530)** > > Associations are a set of macro-like class methods for tying objects together through foreign keys. ---
**Author:** ![allen](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/bbce88/32.png) [@allen](https://www.ruby-forum.com/u/allen)\ **Post date:** [April 6, 2007, 10:33pm UTC](https://www.ruby-forum.com/t/questions-about-activerecord-aggregation/91295/3 "2007-04-06T22:33:26Z")
On 4/6/07, allen [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Hi all, > > I’m quite new to rails. These may be silly questions, but I really > need your advice. Not silly. Just inexperienced. According to \<\>, composite objects > in aggregation are value objects, which means their values cannot be > changed. So if say Person is the model class and Address is the > composite class, the way to update a person’s address is to create a > new Address object, assign it to the person and then save. Not the case, in actuality. You can do person.address.zipcode = ‘63201’ person.address.save or (since you said aggregation), address1 = person.addresses[0] address1.zipcode = ‘63201’ address1.save This works > together. Is there a way to avoid this? Or this is just the way rails > work? If you only need to update one column, you can use lines such as: person.address.update\_attribute(“zipcode”, “63102”) I was thinking about split this big table into several small ones, but > this doesn’t seem to be reasonable in a OO perspective. Do I have to > split the table in order to hold performance or is there better way? > > Aonther question is about multi-layer aggregation, say I want to model > a table into A, B, C there classes and use a a.b.c relationship. Is > this possible? Absolutely, as the other poster said. It is a standard practice in Rails. Thanks a lot. You’re welcome 🙂 ---
**Author:** ![allen](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/bbce88/32.png) [@allen](https://www.ruby-forum.com/u/allen)\ **Post date:** [April 7, 2007, 12:44pm UTC](https://www.ruby-forum.com/t/questions-about-activerecord-aggregation/91295/4 "2007-04-07T12:44:29Z")
Thanks for your patient explanation. Where can I get a close look to all this rails API besides the online document on the offical web site. Is there a downlaodable version? Since I cannot stay online all the time. Another question: Say I want to create a composite class with 20 properties, must I create the initialize method using all these properties? This is boring and easy-mistaken. Is there a better way to do this? ---
**Author:** ![allen](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/bbce88/32.png) [@allen](https://www.ruby-forum.com/u/allen)\ **Post date:** [April 7, 2007, 12:36pm UTC](https://www.ruby-forum.com/t/questions-about-activerecord-aggregation/91295/5 "2007-04-07T12:36:29Z")
Thanks, man. This really helps a lot. On 4ÔÂ7ÈÕ, ÉÏÎç3ʱ08·Ö, Jamal S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) ---
**Author:** ![allen](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/bbce88/32.png) [@allen](https://www.ruby-forum.com/u/allen)\ **Post date:** [April 9, 2007, 3:41am UTC](https://www.ruby-forum.com/t/questions-about-activerecord-aggregation/91295/6 "2007-04-09T03:41:44Z")
Thanks for your reply, but I don’t quite get it for the second question. What do you mean by “put them all in hash” and “instance[hash]”? On Apr 8, 1:24 am, Jamal S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) ---
**Author:** ![allen](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/bbce88/32.png) [@allen](https://www.ruby-forum.com/u/allen)\ **Post date:** [April 9, 2007, 12:59pm UTC](https://www.ruby-forum.com/t/questions-about-activerecord-aggregation/91295/7 "2007-04-09T12:59:27Z")
> If you only need to update one column, you can use lines such as: > person.address.update\_attribute(“zipcode”, “63102”) just want to clear this up. update\_attribute() does not just update a single column in the database. it updates the single attribute in the model then saves the record… same as doing model.some\_attribute = ‘foo’ model.save ---
**Author:** ![allen](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/bbce88/32.png) [@allen](https://www.ruby-forum.com/u/allen)\ **Post date:** [April 7, 2007, 7:24pm UTC](https://www.ruby-forum.com/t/questions-about-activerecord-aggregation/91295/8 "2007-04-07T19:24:55Z")
allen wrote: > Thanks for your patient explanation. Where can I get a close look to > all this rails API besides the online document on the offical web > site. Is there a downlaodable version? Since I cannot stay online all > the time. One way 1. Download Rails sources (svn export [http://dev.rubyonrails.org/svn/rails/trunk](http://dev.rubyonrails.org/svn/rails/trunk) target\_dir) 2. cd target\_dir/railties 3. rake 4. This gives you a target\_dir/rails/doc/api/index.html, containing the complete Rails API docs. Source: [http://article.gmane.org/gmane.comp.lang.ruby.rails/6047](http://article.gmane.org/gmane.comp.lang.ruby.rails/6047) Google: [download rubyonrails doc - Google-søgning](http://www.google.dk/search?q=download+rubyonrails+doc&btnG=S%C3%B8g&hl=da) Keyword: download rubyonrails doc > Another question: Say I want to create a composite class with 20 > properties, must I create the initialize method using all these > properties? This is boring and easy-mistaken. Is there a better way to > do this? It will be easier for you to put them all in hash instance[hash] ---
**Author:** ![allen](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/bbce88/32.png) [@allen](https://www.ruby-forum.com/u/allen)\ **Post date:** [April 9, 2007, 8:30pm UTC](https://www.ruby-forum.com/t/questions-about-activerecord-aggregation/91295/9 "2007-04-09T20:30:30Z")
On 4/9/07, Chris H. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > same as doing > > model.some\_attribute = ‘foo’ > model.save And, a further clarification… it is actually the same as model.some\_attribute = ‘foo’ model.save(false) update\_attribute does not perform validation update\_attributes does perform validation.