# Legacy DB with multiple tables per model **URL:** \ **Category:** Rails\ **Created:** [November 15, 2007, 1:39pm UTC](https://www.ruby-forum.com/t/legacy-db-with-multiple-tables-per-model/120275 "2007-11-15T13:39:09Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![kimmoke](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/e19adc/32.png) [@kimmoke](https://www.ruby-forum.com/u/kimmoke)\ **Post date:** [November 15, 2007, 1:39pm UTC](https://www.ruby-forum.com/t/legacy-db-with-multiple-tables-per-model/120275/1 "2007-11-15T13:39:09Z")
I’m working with a large DB that is also being used by another application(s) so I really can’t change it. I’d like to wrap it in ActiveRecord (or DataMapper/OG/Other ORM) models but it’s quite a challenge because models (in db) have so many parameters that they have been split across multiple tables. Views (on db) don’t come into question since that would create huge joins and fetch far to much data at once. The DB structure probably has been generated by a program so it follows some sort of logic, but I’m ok with the idea that I’m going to have to map the thing once manually. Another annoyance is the fact that the columns in the extra parameter tables are prefixed with a short form of the table name, of course I’d like to access them by the unprefixed name (there aren’t duplicate names) since I don’t want to keep looking up the table number where certain parameters are located (to use Ci.ipv6address instead of Ci.xcit4\_ipv6address) Here’s an example model of ConfigurationItem in the DB (I’ve only picked several tables and parameters for clarity): CDM\_CONFIGURATION\_ITEMS - CIT\_OID - CIT\_CPU\_OID - CIT\_NAME1 - CIT\_NAME2 CDM\_CONFIGURATION\_ITEMS\_X - XCIT\_CIT\_OID - XCIT\_PURCHASEDATE - XCIT\_CINUMBER1 CDM\_CONFIGURATION\_ITEMS\_X\_SD\_1 - XCIS1\_CIT\_OID - XCIS1\_CITEXT91 - XCIS1\_IPADDRESS CDM\_CONFIGURATIO\_ITEMS\_X\_SD\_10 (n dropped from configuration when going over 9) - XCISA\_CIT\_OID (notice, after 9 comes A) - XCISA\_SHORTTEXT36 CDM\_CONFIGURATIO\_ITEMS\_X\_SD\_18 - XCISI\_CIT\_OID - XCISI\_SERIALNUMBER I’d like to do something like \<%= ConfigurationItem.find(:first).ipadress %\> which would on demand make a query that gets the value (or eager load all values) from CDM\_CONFIGURATION\_ITEMS\_X\_SD\_1. Also it would be great to do something like @cis = ConfigurationItem.find(:all, :include\_fields =\> [:citext91, :name2]) that would magically create joins for the required tables. I won’t do any writing through the DB connection, all of it is done via a Java API which I have been using through JRuby successfully, but that’s another story. A colleague of mine already did this in lisp and of course I’d like to show that ruby isn’t bad either. Ideas? Discuss 🙂 ---
**Author:** ![kimmoke](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/e19adc/32.png) [@kimmoke](https://www.ruby-forum.com/u/kimmoke)\ **Post date:** [November 15, 2007, 9:13pm UTC](https://www.ruby-forum.com/t/legacy-db-with-multiple-tables-per-model/120275/2 "2007-11-15T21:13:40Z")
On Nov 15, 7:39 am, Kimmo L. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: [http://groups.google.com/group/rubyonrails-talk/browse\_thread/thread/f1d4421eb73b2d9c](http://groups.google.com/group/rubyonrails-talk/browse_thread/thread/f1d4421eb73b2d9c) Well, I suppose that if you have time, you can build up some network of Ruby objects that represent the data schema the way it is in the database, and correspondingly, this data structure could also represent the schema the way you would like to view it from the object world, and it could represent the correspondence between the two. Then you could override enough of ActiveRecord to make it crawl your schema instead of making its current assumptions about the relationships between the object world and the relational world.