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