Re: [SQLObject] Foreign Key + Constraints?

[Sidnei da S. <si...@aw...>]

On Wed, Dec 03, 2003 at 01:25:43PM -0600, Ian Bicking wrote:
| I haven't looked at the patch in context yet, but a couple comments...
| 
| >Second, I think that as I'm getting the 'dependent'[1] classes via
| >findDependencies, It would be simple to pass them into
| >DBConnection.dropTable() so that we can do the cascade the manual way
| >-- by iterating on the result of select() and calling destroySelf() on
| >each object. Does that sound reasonable?
| 
| You mean, delete every instance from the table, then delete the table?  
| Hmm... dropping a table is a pretty severe thing whatever way you do 
| it, I'm not sure how important destroySelf is at that point.  OTOH, 
| maybe if you just want to drop without any checks (and presumably 
| restart your process), you should do it with plain SQL and not the 
| class method.  (E.g., test code will want to do that drop, so it can 
| start from a consistent state regardless of previous possible 
| corruption)

Ok, I think I misunderstood Postgres here. I though that 'DROP TABLE
$tablename CASCADE' would remove the dependant records from the other
tables, but that doesn't seem to be true. It changes the dependant
tables only when you delete a row, which is good. I didn't had
understood that.

| >[1] I considered 'dependent' a class that has a column which refers to
| >our class on the 'foreignKey' attribute, and also has 'cascade' set to
| >True.
| 
| I suppose it follows that if the rows are dependent, the table as a 
| whole is as well.  OTOH, that wouldn't occur to me naturally -- it's 
| something of a corner case.  The principle of least surprise would 
| indicate that we should leave the table around.  But that's no good, as 
| we're inconsistent at that point.

I don't follow you 100% here, but I think its related to the above comment.

| And what about circular dependencies?  These can only happen if NULL is 
| also allowed in the foreign key, but it does happen.  In this case we'd 
| want to NULL out the one table, remove the first, then maybe remove the 
| second.

I didn't understood this one as well.

-- 
Sidnei da Silva <si...@aw...>
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