generate top-level python code for an alembic revision from render_item

[Adrian]

I have a custom type implementing enums (no idea if there's something better now, but it's used in many places so

replacing it is not an option atm). Currently I'm using render_item to simply import the type and the enum and pass the

enum to the type and it works fine.

However, in the alembic revision I'd prefer to define a copy of the enum how it looked like at generation time since it may

change and in that case running an older revision's upgrade would be broken as it would generate the column based on

a different enum.

In any case, I would like to have the enum definition inside my revision file, either top-level or inside `upgrade`. But for neither

of these options I found any way to do it properly as there doesn't seem to be any way to provide code to be included in

`upgrade` or variables for the mako template context used to render the revision file.

I managed to do it using this **incredibly ugly** workaround, but I really hope there's some better way... so if there is one, please

let me know. Because not adding this abomination in my codebase would be great:

https://gist.github.com/ThiefMaster/3ad2a35b531ff5cada7d2232333619fa

Thanks for any help/suggestions!

[Mike Bayer]

it's pretty doable if you add a new ${thing} to your mako template.  getting a value in there requires a trick, there's an example of it here:    https://github.com/sqlalchemy/alembic/issues/686#issuecomment-616828129

which is to put a dictionary inside of another dictionary and pass that as "template_args" when you context.configure(); suppose you send it as template_args={"my_dictionary": {}}.  then anywhere you are, in a render hook, in env.py, whatever, put whatever you want in that dictionary.   then reference in your template as ${my_dictionary['some_value']} .

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[Adrian]

 Works great, thanks!