[development] One-to-one tables considered harmful

[Gabor Hojtsy]

Mark Fredrickson wrote:
> Flame war aside, I think there are some good points in this thread.
> Perhaps someone can clarify two points:
> 
> 1. Is it kosher to add columns to other modules' tables? E.g. Is it ok
> for comment to add it's statistics to the node table. Similarly, I
> could imagine the stats module would want to add summary information,
> and perhaps other modules as well.

The problem with dynamically modifying other module's tables has one 
glaring problem: the upgrade path. Now let's take menu module or locale 
module. Locale module had the locales_meta table in Drupal 5. If contrib 
modules added columns to this table, the column and the data will be 
completely lost, since the Drupal 6 upgrade creates a new "languages" 
table, gets the data **which is expected by locale module to be there** 
in the old locales_meta table and finally drops the locales_meta table. 
So only the data handled by the module will be saved.

Similar issues can arise when data is updated only, if you would do 
updates in your custom columns in those algorithms too. Or the module 
update might try to add a column named as the one which was put there by 
some of your other modules.

So as long as you modify someone else's (either core module or contrib, 
does not matter) table in a contrib module, you fork Drupal, and you are 
on your own to handle the situations that can possibly arise.

Optimizing *core* functionality by putting related data together is a 
different question though.

> 2. Do David's arguments support more Single Table Inheritance[1] in
> Drupal (e.g. adding columns to node that don't necessarily apply to
> every node type)? For example, should CCK add columns to the node
> table that only apply to some types of nodes.

Hm, the node table already has a newly added column in Drupal 6 to store 
the language code, and this is not managed in node module. Dries also 
requested to add node translation related fields directly into the node 
table underlining that this is a core feature (even if you don't have 
the node translation module enabled). [Node translation is still in the 
works, look here: http://drupal.org/node/142280 ]

I would not advise any contrib module to modify anyone else's core or 
contrib table, but feel free to play along with their own tables as they 
wish. I don't think it is a good idea maintanance wise for CCK to modify 
the node table directly, although it might look performance wise attractive.

Gabor