Migrate from weppy to emmett [migrations]

[josejachuf]

I am to migrate an app from Weppy to Emmett (Postgresql). Weppy's already has a migration history. What would be the best way to do this and continue with migrations in Emmett?

It seems to me that the use of "set" can be useful, but I'm not sure.

What I had thought is something like that (they are two different servers):

1. Weppy database backup and restore in Emmett server
2. Move Weppy migration directory to Emmett and correct imports:
   from weppy.orm import migrations to from emmett.orm import migrations
3. rename weppy_schema to emmett_schema
4. Run the migrations (new model) in a normal way

Some help that can give me

[gi0baro]

@josejachuf sorry for the late reply. I'll use the migrations set command instead of manually renaming the schema table, so:

• dump and restore
• move and patch migrations as you said
• use migrations set command with the last hash from weppy schema

Proceeding this way, you can test if everything went as supposed running migrations up right after and checking the system does nothing. Then you can just drop the weppy_schema table.

[josejachuf]

Thanks @gi0baro
I will try it during the week.

[josejachuf]

Hi @gi0baro
The following error occurred for me. I believe the error occurred because initially there are no records in emmett_schema. Nevertheless, I did it manually without using 'set' and it worked fine.

/www/venv/bin/emmett -a app migrations set -r f45113b897f5
> Setting revision to f45113b897f5 against postgres://...
Do you want to continue? [y/N]: y
Traceback (most recent call last):
  File "/www/venv/bin/emmett", line 8, in <module>
    sys.exit(main())
             ^^^^^^
  File "/www/venv/lib/python3.11/site-packages/emmett/cli.py", line 513, in main
    cli.main(prog_name="python -m emmett" if as_module else None)
  File "/www/venv/lib/python3.11/site-packages/emmett/cli.py", line 236, in main
    return super().main(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/www/venv/lib/python3.11/site-packages/click/core.py", line 1078, in main
    rv = self.invoke(ctx)
         ^^^^^^^^^^^^^^^^
  File "/www/venv/lib/python3.11/site-packages/click/core.py", line 1688, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/www/venv/lib/python3.11/site-packages/click/core.py", line 1688, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/www/venv/lib/python3.11/site-packages/click/core.py", line 1434, in invoke
    return ctx.invoke(self.callback, **ctx.params)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/www/venv/lib/python3.11/site-packages/click/core.py", line 783, in invoke
    return __callback(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/www/venv/lib/python3.11/site-packages/click/decorators.py", line 92, in new_func
    return ctx.invoke(f, obj, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/www/venv/lib/python3.11/site-packages/click/core.py", line 783, in invoke
    return __callback(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/www/venv/lib/python3.11/site-packages/emmett/cli.py", line 509, in migrations_set
    set_revision(app, dbs, revision, auto_confirm)
  File "/www/venv/lib/python3.11/site-packages/emmett/orm/migrations/commands.py", line 438, in set_revision
    Command(app, dals).set(revision, auto_confirm)
  File "/www/venv/lib/python3.11/site-packages/emmett/orm/migrations/commands.py", line 388, in set
    self._store_current_revision_(
  File "/www/venv/lib/python3.11/site-packages/emmett/orm/migrations/commands.py", line 159, in _store_current_revision_
    ctx.db.Schema.version == source[0]
                             ~~~~~~^^^
IndexError: tuple index out of range

Thanks!

[gi0baro]

@josejachuf can you open up an issue for this? migrations set should always work, even with no existing schema