Alembic Spanner DB Table Creation, Duplication Issue.

[kumarlti]

While running Alembic migration file for GCP Spanner for creating the Table. The migration file runs and the table is created but the issue is that the migration tries to run again and as the required table has already been created it gives an Error that the the required table already exists in the schema and thus the migration fails.
Can anyone please suggest how to stop the the migration file from re running in case GCP Spanner DB.

[CaselIT]

Hi,

Is the alembic version table correctly updated to register that the migration was run?

[kumarlti]

No as migration is not successful and complete itself, there's only alembic_version table is created but it doesn't have any rows.

[CaselIT]

Sorry but I don't follow. You said

The migration file runs and the table is created but the issue is that the migration tries to run again

I interpreted this as the first run on "alembic upgrade" works fine, but trying to run it again causes the problem.
If that's not correct can you state all the steps you are doing and what's failing?

[kumarlti]

So, it goes as below:
i) Initially we define our models in models.py file.
ii) Then we run the "alembic revision --autogenerate -m 'message'". This creates a new migration file in alembic folder in the project.
iii) Also when we check our Spanner instance schema/DB, there is a alembic_version table get created.
iv) Finally when we run "alembic upgrade head" command to execute the migration file/files present, it creates the mentioned table/models in the DB but it doesn't stop and tries to again create the mentioned table(as we assume) because everytime it gives the error as the given table already exists in the schema, duplicate can't be created, for the given run. Eventually the migration file run fails and no new row is created in the alembic_version table.

[CaselIT]

that's very wired.
on step iii can you verify that the tables that would be created by the migration file are not present in the db?

alembic has no logic to re-run a single migration, so if there is no table on step iii and there is only a single create_table line in the migration file I don't know how that line could be run twice.

Can you turn on the engine echo so that all the statement are logged to the console?

[kumarlti]

Yes, in step iii) there is no pre existing table in the DB