Embedding templates in the Alembic repository

[matrixise]

Hi,

The idea of having a template for generating migration scripts is really great, but I think we can go further.

For example, embedding templates in a ./templates directory that would contain several templates, one for table creation, or for adding columns.

From there, we could specify which template we want to use when writing a new revision.

For example:

alembic revision --template add_table -m "Add User table"
alembic revision --template add_column_table -m "Add UUID for the user table"

I mention this because customizing a template script with all the options on the command line is becoming increasingly difficult to maintain.

[zzzeek]

this would be a straightforward feature to add and seems like it should be possible, though id like to understand your use case better. what are "all the options on the command line" that you're passing?

[zzzeek]

if the varchar to enum case is the main rationale, why dont we fix that case ? We likely need a dedicated alembic construct for that.

Having a "template" for varchar-> enum means you want to create a migration that does exactly one change to a single column. if I were burdened by the "varchar->enum" case and I didnt have time to contribute to #278, I wouldn't want a template. I'd make a Python function to do it! The import for my python function would be part of my single alembic template so that I can use it when I need it.

Why "templates" and not "modules with helper functions" ? the latter seems much more obvious and generally useful.

[zzzeek]

similarly, rename a table, why do we need a template for that? use the function ? it's one line? How would --template work with that ? would there also be command line arguments for table name, schema name, column name, etc. ? This seems way out of scope for alembic itself.

[zzzeek]

Here's screenshots of using vscode - rename table is right in the dropdown, argument names, works great, nothing new to learn outside of your IDE, this seems a lot easier to me if people are writing templates by hand...

[matrixise]

it was a simple idea, I think we can close the issue.

[zzzeek]

whoops I hope I didnt offend, these are the questions I'd be asking of any feature that we add to alembic or SQLAlchemy. As proposed the option seems simple and possibly useful but after many years of doing this I've learned that anything you add has to fit into a bigger story of how the library / application is going to be used. otherwise you are just adding things for the sake of adding them, and possibly missing the best way for something to be added, which can then make it hard to change later. so I was just looking for what these templates would be doing in terms of what kinds of problems you want to solve and how it would look in practice.