# ActiveRecord bottom half **URL:** \ **Category:** Rails\ **Created:** [July 7, 2007, 5:57pm UTC](https://www.ruby-forum.com/t/activerecord-bottom-half/108823 "2007-07-07T17:57:10Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![pedz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/839c29/32.png) [@pedz](https://www.ruby-forum.com/u/pedz)\ **Post date:** [July 7, 2007, 5:57pm UTC](https://www.ruby-forum.com/t/activerecord-bottom-half/108823/1 "2007-07-07T17:57:10Z")
I want a different way of doing polymorphic records. One problem I have is validates\_presence\_of does not work for me – and no one replied to my question. I am finding it hard to make sure the database stays consistent. What I want to do is create a table that has a unique id and a string which will be the type. The other tables that type will point to will have the same id and the attributes for that type. So, the first table may be items and items could reference people, companies, etc. The key to people, companies, etc is the same id as for item – i.e. if you union all of the sub tables, you will have each id at most one time. I believe, using PostgreSQL’s features, this will be easier to keep consistent. Of course, I may find out that I’m full of BS. But, part of the knowledge I need to gain is how ActiveRecord goes from the blob of mess that the database returns to an instance of a particular class. If anyone can help me out and tell me where to look, etc, that would be much appreciated. Thank you, Perry S. Ease Software, Inc. ( [http://www.easesoftware.com](http://www.easesoftware.com) ) Low cost SATA Disk Systems for IBMs p5, pSeries, and RS/6000 AIX systems ---
**Author:** ![pedz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/839c29/32.png) [@pedz](https://www.ruby-forum.com/u/pedz)\ **Post date:** [July 7, 2007, 6:58pm UTC](https://www.ruby-forum.com/t/activerecord-bottom-half/108823/2 "2007-07-07T18:58:55Z")
Hi Perry, Perry S. wrote: > What I want to do is create a table that has a unique id > and a string which will be the type. The other tables that > type will point to will have the same id and the attributes > for that type. So, the first table may be items and items > could reference people, companies, etc. The key > to people, companies, etc is the same id as for item – i.e. if you > union all of the sub tables, you will have each id at most one time. Your description above contains much that we allow Rails and AR to manage for us. One of the key things with Rails is that primary keys are meaningless to us. Only AR cares about them, and we let it take control of them to make it easier for us to focus on the application itself rather than the management of the data the app uses. You’ll find it a lot easier to work with Rails, and to get help here too IME, if you can start by answering: “From a user perspective, what problem are you solving? What is it you’re trying to allow the user to do with your application?” > I believe, using PostgreSQL’s features, this will be easier > to keep consistent. Of course, I may find out that I’m full > of BS. I haven’t used PostgreSQL with Rails, but don’t have the impression from seeing OP’s posts that it’s any easier or harder than any other supported DB with Rails. > But, part of the knowledge I need to gain is how ActiveRecord > goes from the blob of mess that the database returns to an instance > of a particular class. Depending on exactly what your objective is, you may or may not need to know the above in order to achieve your objective. Probably not. In general, our apps deal in objects, we tell AR how the objects are related, it handles the ORM mapping, and we’re happy for it. > If anyone can help me out and tell me where to look, > etc, that would be much appreciated. I’d start out by trying to regain my “beginner eyes.” Will R. said “It’s not what we don’t know that hurts. It’s what we know that ain’t true.” To be successful with Rails, you’re probably going to do quite a bit of ‘unlearning.’ That’s just speculation on my part, based on a year and a half of observation / participation here on the list. There are a number of beginner tutorials out there. With all things Rails, Google is your friend. You may find it too elementary for you, but you might want to start with: > **[Radar - O’Reilly](https://www.oreilly.com/radar/?page=1)** > > Now, next, and beyond: Tracking need-to-know trends at the intersection of business and technology hth, bill ---
**Author:** ![pedz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/839c29/32.png) [@pedz](https://www.ruby-forum.com/u/pedz)\ **Post date:** [July 7, 2007, 7:21pm UTC](https://www.ruby-forum.com/t/activerecord-bottom-half/108823/3 "2007-07-07T19:21:38Z")
Bill W. wrote: > Hi Perry, > > Perry S. wrote: > > > What I want to do is create a table that has a unique id > > and a string which will be the type. The other tables that > > [snip] > > hth, > > bill The big thing that is frustrating me with the existing methods is how to do validation. As I said, I can not get validates\_presence\_of to work for me in a polymorphic belongs\_to. I’m torn between trying to do validation up in Rails or down in the DB. As I said, this may be all folly but I’ve implemented the application (the basic functions) using the standard Rails concepts. But, I can not figure out how to make sure the thing the belongs to association really does exist and I can not figure out a way to prevent it from being deleted before everything that points to it is deleted first. Those two things is what led me down this journey. What I am trying to do is just subtly different for sure but the rearrangement of the tables and keys will make the DB validation part much easier. It also reduces the amount of redundant information. The only thing that PostgreSQL gives me is rules and stored procedures to do the validation in the DB. I’m not sure but I think those are not in other DB’s. To recap, I’m not wanting to go down this path. I just want to validate the database and keep it valid at all times. ---
**Author:** ![pedz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/839c29/32.png) [@pedz](https://www.ruby-forum.com/u/pedz)\ **Post date:** [July 7, 2007, 7:36pm UTC](https://www.ruby-forum.com/t/activerecord-bottom-half/108823/4 "2007-07-07T19:36:59Z")
Hi Perry, Perry S. wrote: > The big thing that is frustrating me with the existing > methods is how to do validation. As I said, I can not > get validates\_presence\_of to work for me in a > polymorphic belongs\_to. It would be easier to help if you posted the SQL script or migration that you’re using to create the tables and the related models. > I’m torn between trying to do validation up in Rails > or down in the DB. We do validations in our models. Rails treats the DB as a simple container. My experience is that that’s the only viable option if you want the freedom to change databases. > The only thing that PostgreSQL gives me is rules and stored > procedures to do the validation in the DB. I’m not sure but I > think those are not in other DB’s. They’re not in some, and they’re handled differently in others. It’s one of the fundamental ways that database vendors achieve lockin. Being locked in to an open source DB is still being locked in. Not good, IMHO. > To recap, I’m not wanting to go down this path. I just > want to validate the database and keep it valid at all times. That’s not going to be a problem, assuming you’re willing to let Rails and AR do their thing, rather than impose a preconceived solution on them. Post some code. Best regards, Bill ---
**Author:** ![pedz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/839c29/32.png) [@pedz](https://www.ruby-forum.com/u/pedz)\ **Post date:** [July 7, 2007, 7:44pm UTC](https://www.ruby-forum.com/t/activerecord-bottom-half/108823/5 "2007-07-07T19:44:43Z")
Bill, Please see: [http://www.ruby-forum.com/topic/113189#new](http://www.ruby-forum.com/topic/113189#new) I may have discovered the error of my ways. Instead of validates\_presence\_of, should I be using validates\_associated ? ---
**Author:** ![pedz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/839c29/32.png) [@pedz](https://www.ruby-forum.com/u/pedz)\ **Post date:** [July 7, 2007, 9:18pm UTC](https://www.ruby-forum.com/t/activerecord-bottom-half/108823/6 "2007-07-07T21:18:10Z")
Hi Perry, Perry S. wrote: > Please see: > > [Validates\_presence\_of of polymophic fields - Rails - Ruby-Forum](http://www.ruby-forum.com/topic/113189#new) > > I may have discovered the error of my ways. Instead of > validates\_presence\_of, should I be using validates\_associated ? What you don’t say in your post above is whether or not you’re getting the results you expect. If it accomplishes what you’re trying to accomplish, use it. Rails typically gives us more than one way to “skin the cat.” Without knowing what you’re trying to accomplish it’s not possible to say whether or not there’s an easier / more Railsy way to do it. I assume you’ve reviewed the documentation on validates\_associated at [http://api.rubyonrails.org](http://api.rubyonrails.org) and seen the note re: the potential need to use validates\_presence\_of on the association itself. Best regards, Bill ---
**Author:** ![pedz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/839c29/32.png) [@pedz](https://www.ruby-forum.com/u/pedz)\ **Post date:** [July 7, 2007, 9:35pm UTC](https://www.ruby-forum.com/t/activerecord-bottom-half/108823/7 "2007-07-07T21:35:36Z")
Bill W. wrote: > Hi Perry, > > What you don’t say in your post above is whether or not you’re getting > the > results you expect. I thought I did. The validates\_presence\_of always produces an error. I’m trying to make sure that the child and parent have been set and are not null. At the time validate gets called, child\_id and child\_type are not set (according to my logging). But they get set before they actually get saved. The relationship is being saved because I have appended it to @person.children. i.e. ``` @person.children << relationship (as you can see in my other post). ``` So, somehow, before the data actually is shipped off to the database but after the validation sequence, the child\_id and child\_type get filled in. I’m still trying to debug this and find a way to get this to work. I thought I had it figured out but the last test didn’t work. Oh, also, if I do both: ``` @person.children << relationship relationship.child = @person ``` that causes an infinite recursion. This seems pretty basic. I must be doing something really silly but I don’t know what it is.