Building Data-Driven Web Apps with Pyramid and SQLAlchemy Transcripts
Chapter: Database migrations with Alembic
Lecture: Concept: auto-generating changes
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The best way to use a Alembic, I think is to let SQLAlchemy at least prebuild the various revision changes for you
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and then you can edit them still if you like. In order to do that, you have to edit the env.py file and you have to set the target metadata
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to the SQLAlchemyBase.metadata. And just like before, it is super important that that SQLAlchemyBase thing sees all of your various models.
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That means you have to do some form of import like this from pypi.data import * or something to that effect to make sure that everything is loaded up.
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But adding these two things we'll connect SQLAlchemy and Alembic so that Alembic can use your models
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to generate the revisions. And that is way, way sweeter. So just simply setting this target metadata
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is all we have to do to connect our ORM models to Alembic. And then to make a change, we just add the auto generate like we had before but now we say
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auto generate this change. It's going to go detect the various changes and it's going to create another one of these files.
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We open up that file and now, it's better. We have this little section in upgrade. Instead of pass, it says, "These were auto generated
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"by Alembic, please review them and if you're happy "just leave them, or if you need to, make changes." Nothing happens when you auto generate this
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but it generates the file if it can guess and then you edit it to do what it needs. Finally you just apply it again
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and it's going to apply that auto generated revision change rather than the one you had to manually write. And that's Alembic.
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A various nice way to keep evolving your database structure along with the evolution of your SQLAlchemy models
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and for the most part making that automatic.