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How to Use tgadmin sql upgrade with SQLObject

The tg-admin script that is bundled with TurboGears is really helpful, but I had a hard time learning how to use it.

These are my notes on how I use tg-admin to upgrade an existing database.

  • I have a production database that uses prod.cfg;
  • I have a development database that uses dev.cfg;
  • Neither databases have a sqlobject_db_version table initially, because I never payed attention to it yet.

The development database has a bunch of new columns, tables, and indexes that I want to add to the production database. For this example, I’ll pretend that all I want to do is add an index to a table.

First, I made sure that the dev database matches sqlobject classes:

tg-admin -c dev.cfg sql status

If those are out of sync, then do whatever you need to do to make sure your actual dev database matches your classes. Of course, tg-admin sql status is not perfect. For example, it overlooks missing indexes and constraints, at least with postgres.

Next, I recorded the state of the development database:

tg-admin -c dev.cfg sql record --force-db-version=2008-03-21

This will make a new table in the dev database called sqlobject_db_version. I am forcing it to have a value of today’s date (March 21st, 2008).

Now I connect to the production database and set a version on it with yesterday’s date:

tg-admin -c prod.cfg sql record --force-db-version=2008-03-20

Now I run this to try to upgrade the production database to match the development database:

tg-admin -c prod.cfg sql upgrade

Of course, that should fail, and I see some error message sort of like this:

$ tg-admin -c prod.cfg sql upgrade
Using database URI postgres://staffknex:staffknex@localhost/staffknex320
No way to upgrade from 2008-03-20 to 2008-03-21
(you need a 2008-03-20/upgrade_postgres_2008-03-21.sql script)

This is an example of a helpful error message. I need to write a script that will explain how to upgrade from yesterday’s version to today’s version.

That script will be really simple:

CREATE UNIQUE INDEX majestic12 ON ufo_theorists (first_name, last_name);

I suggest using BEGIN and END so that in case something goes wrong in the middle, your transaction will be rolled back automatically.

Now I can run this:

tg-admin -c prod.cfg sql upgrade

And my production database will be upgraded with the new index.

Now for some complaints:

  • Why isn’t this advertised better? This is a really nice feature.
  • You’re supposed to be able to specify the URI on the command-line with the – connection option, but I could never get it to work.
  • I really wish that tg-admin sql status detected stuff like missing indexes and constraints. I use these things heavily.
  • It would be nice to be able to mix python into the upgrade script, rather than just SQL. For example, I recently dropped a column that had both an employee’s first and last name, and separated this into two columns. I used SQL to make the new columns, then I used python to read data out of the old single column and write it to the two new columns. Then I used SQL again to drop the old column.

Like I said at the beginning, this is a really helpful script and I’m very grateful to whoever wrote it.