Application defaults go in the application code not in the database (my
opinion).
If you wants user, group, whatever customizable defaults, they belong in the
database schema i.e. table user_prefs or role_prefs
For your question about "backwards compatible database", in most cases apps
and databases schemas are upgraded at the same time.
If you have a requirement that old & new apps have to work on the same
database schema then don't make database schemas changes that will not be
backwards compatible / break older apps.
Put those changes on hold until both apps & databases can be upgraded. Some
solutions which may help you java (hibernate) adds a version column to each
table, rails adds a schema_info table with database version.
The are many ways of managing applications upgrades, it's an mainly an
application challenge not a database design issue.
-----Original Message-----
From: pgsql-general-owner@postgresql.org
[mailto:pgsql-general-owner@postgresql.org] On Behalf Of David
Sent: June 18, 2008 8:03 AM
To: pgsql-general@postgresql.org
Subject: [GENERAL] Database design: Storing app defaults
Hi list.
If you have a table like this:
table1
- id
- field1
- field2
- field3
table2
- id
- table1_id
- field1
- field2
- field3
table1 & table2 are setup as 1-to-many.
If I want to start providing user-customizable defaults to the
database (ie, we don't want apps to update database schema), is it ok
database design to add a table2 record, with a NULL table1_id field?
In other words, if table1 has no matching table2 record, then the app
will use the table2 record with a NULL table1_id field to get
defaults.
This looks messy however. Is there a better way to do it?
A few other ways I can think of:
1) Have an extra table1 record (with string fields containing
'DEFAULT'), against which the extra table2 record is linked.
2) Have a new table, just for defaults, like this:
table2_defaults
- field1
- field2
- field3
Which is the cleanest way? Is there another method I should use instead?
David.
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