Failing to create revision using alembics "Offline Mode"

Thanks for this tool. Enums were always a pain to manage in my revisions.

A big part of my application relies on alembics "Offline Mode" (https://alembic.sqlalchemy.org/en/latest/offline.html) to generate revisions as SQL file e.g. alembic upgrade base:head --sql > test.sql. Unfortunately this currently does not work with alembic-postgresql-enum.

The issue is that an offline migration can not contain any statement that pulls some results into memory via a SELECT.

https://github.com/Pogchamp-company/alembic-postgresql-enum/blob/aefabbec350abb3938f6f3d269cac0883bad00e9/alembic_postgresql_enum/enum_alteration.py#L61C1-L68C23

therefore throws 'NoneType' object has no attribute 'scalar' error when using --sql option.

I was able to get it working by changing the linked lines to

default_value = None
if context.is_offline_mode():
    connection.execute(...)
else:
    default_value = connection.execute(...).scalar()

However, I guess this might interfere with the correct handling of default values, but for my use case where I don't have any default values it seems to work fine. Maybe you want to consider adding support for offline revisions (or if that is not an option, then a note to the readme mentioning that offline revisions are currently not possible could be helpful)

I'll explore alternatives for handling default values

Thanks for the quick action. Unfortunately, this issue is not solved. None of the linked changes addresses my initial problem.

The get_column_default function still fetches columns which will not work in Offline Mode.

The same error still persists ( 'NoneType' object has no attribute 'scalar') as a result of this section:

alembic-postgresql-enum/alembic_postgresql_enum/sql_commands/column_default.py

Lines 17 to 24 in 5780119

    
               default_value = connection.execute(sqlalchemy.text(f""" 
        
                   SELECT column_default 
        
                   FROM information_schema.columns 
        
                   WHERE  
        
                       table_schema = '{schema}' AND  
        
                       table_name = '{table_name}' AND  
        
                       column_name = '{column_name}' 
        
               """)).scalar()

This update tweaked the way migrations generate. Have you tried generating a new one?

I am pretty sure that your update did not touch anything related to alembics offline mode.

You can introduce the following test case to see the error yourself. Notice the optional parameter in MigrationContext.configure(connection, opts={'as_sql': True}) which is passed by alembic to the migration context when offline mode is used (e.g. when using the --sql flag on the command line).
This test case will currently fail.

def test_sync_enum_values_offline(connection: 'Connection'):
    old_enum_variants = ["active", "passive"]

    database_schema = get_schema_with_enum_variants(old_enum_variants)
    database_schema.create_all(connection)

    new_enum_variants = old_enum_variants.copy()
    new_enum_variants.append('banned')

    mc = MigrationContext.configure(connection, opts={'as_sql': True})
    ops = Operations(mc)

    ops.sync_enum_values(DEFAULT_SCHEMA, USER_STATUS_ENUM_NAME, new_enum_variants,
                         ((USER_TABLE_NAME, USER_STATUS_COLUMN_NAME),))

New migrations will contain:

 ops.sync_enum_values(DEFAULT_SCHEMA, USER_STATUS_ENUM_NAME, new_enum_variants,
                         [TableReference(USER_TABLE_NAME, USER_STATUS_COLUMN_NAME)])

There is TableReference object instead of tuple. The change was that default value is now saved during migration generation not execution.

When tuple is passed to the function it works the old way to maintain backward compatibility

okay I got it now. Thanks for your help!

	default_value = connection.execute(sqlalchemy.text(f"""
	SELECT column_default
	FROM information_schema.columns
	WHERE
	table_schema = '{schema}' AND
	table_name = '{table_name}' AND
	column_name = '{column_name}'
	""")).scalar()