On Jul 22, 2007, at 10:35 AM, Alvaro Herrera wrote:
Nis Jørgensen wrote:
Alvaro Herrera skrev:
Nis Jørgensen wrote:
What if, for instance, I want to render a list of shapes?
To render the shape, I need to get its data, to get its data, I
need to know what type it is. ISTM that the easiest way to achieve
this is storing the type info at the "top" of the table hierarchy.
Try adding "tableoid" to the list of columns retrieved. Even
better,
cast that to regclass.
This is if I use PG table inheritance, right?
Right, that was what I was thinking.
Right now, I am pretty happy with what I have (but I do have some
extra data).
In what I call my item_base table, I have an item_id and item_type
(integer and string). The type is not the table name but a Class
name. I also have a table that goes from one to the other.
In each of my child (sub-class) tables I have the same tuple. But,
for example, in the companies table, I have an added constraint that
it is set to "Company". I have a "initially deferred" foreign
constraint of item_id and item_type from the child tables to the
item_base table. The item_base table has a check constraint that
translates the item_type to a table name and then verifies that the
id in the referenced table exists. I also have "on delete cascade"
set so they both disappear at the same time.
I do not have item_id in the item_base table of type serial. Instead
I have a sequence number that the child tables get their id from (all
from the same sequence). Then this id is put into the item_base
table. This is because the child table entry must be created first,
then the base because I can not defer the check constraint (which
turns out not to be true but I didn't know that when I started down
this road).
Thank you all for helping,
Perry Smith ( pedz@xxxxxxxxxxxxxxxx )
Ease Software, Inc. ( http://www.easesoftware.com )
Low cost SATA Disk Systems for IBMs p5, pSeries, and RS/6000 AIX systems
