Building Data-Driven Web Apps with Pyramid and SQLAlchemy Transcripts
Chapter: Database migrations with Alembic
Lecture: More database changes
0:00 So we're able to add that change to that column.
0:03 We also added our auditing table, but I commented it out
0:06 so, Alembic wouldn't notice those changes.
0:09 So now let's go over here and we can have it do
0:12 another change. So I'm going to say generate another upgrade
0:17 and this upgrade is going to be adding auditing.
0:24 Now it goes and runs again and says oh, this time we
0:27 are going to create a new table and that table's going
0:29 to have a special index on created date.
0:32 Cool, huh. So let's see what else we got.
0:34 We now have two pieces and this one says
0:37 here's the revision and it derives from it depends
0:41 upon this previous one.
0:42 So this is how they chain together.
0:44 We're going to upgrade.
0:45 It's going to go create the table in the primary key
0:49 and all that. Then it's going to create the index and of course
0:51 dropping that in reverse is what's going to happen
0:53 if we undo it. So let's go and run this.
1:00 Let's get this database updated to the current version.
1:03 Again alembic upgrade head.
1:05 This time it's going to upgrade from this version
1:08 do as many steps as necessary, to that version
1:12 by adding auditing. Now again, what do we get?
1:15 We now have an auditing table, beautiful.
1:18 Granted that auditing table could have been added by
1:20 SQLAlchemy, but suppose that auditing table was defining
1:26 a foreign key and maintainers that linked back to it.
1:28 It wouldn't be all put together correctly.
1:31 Here's how we can use Alembic to manage the structure
1:34 of our database.
1:36 What's really nice is we can use the Auto Generate feature
1:39 here to actually keep it in sync with whatever's happening
1:44 on our database.
1:47 Let's do one more quick thing to round out this lecture.
1:50 At the beginning we asked alembic current to see
1:52 what the version was and it kind of did a no op
1:54 and so that meant there was no version.
1:56 Now we can say alembic current and it will actually
1:59 tell us this is the current version of the database
2:02 and that's the latest as far as Alembic's concerned.
2:04 Double check the state of any database by asking Alembic
2:08 about Current.
2:09 Also in the slides I'm going to talk about this
2:12 alembic_helpers and so I'm dropping this in here
2:15 so you have it. If you want to use the operations that I talk about
2:19 in a moment, but they're not actually used in the demo.
2:22 I'm just including this here for the manual side of things.
2:26 Maybe it will even be helpful in the auto generated
2:29 steps as well. It's especially helpful in the manual bits.
2:33 I'll just throw that in there just so you have it.