Problem with alembic revision --autogenerate: Empty migration file

[sifir-gun]

Hello,

I am encountering an issue with Alembic when trying to generate an automatic migration.

🛠️ Context:
• This is my first time using Alembic.
• I am trying to generate a migration with the following command:

alembic revision --autogenerate -m "Initial migration"

•	The migration file is created inside alembic_migrations/versions/, but it is empty, and I get the following error:

FAILED: Could not determine revision id from filename
a3b8709870ad_initial_migration.py. Be sure the 'revision' variable is declared inside
the script (please see 'Upgrading from Alembic 0.1 to 0.2' in the documentation).

🧩 What I have checked so far:
• I verified that my SQLAlchemy models are properly registered:

python -c "from app.core.database import metadata; print(metadata.tables.keys())"

Output:

dict_keys(['users', 'trades', 'portfolios', 'assets', 'bots', 'dashboard_stats', 'bot_stats', 'account_stats', 'market_stats', 'user_settings', 'notification_settings', 'exchange_accounts', 'subscriptions', 'billing_history'])

✅ The tables are detected correctly by SQLAlchemy.

•	My Alembic configuration (env.py) seems correct:

from app.core.database import engine, Base
target_metadata = Base.metadata

•	I have already tried the following solutions, but the problem persists:
1.	Deleting previous migrations and generating a fresh one:

rm -rf alembic_migrations/versions/*.py
alembic revision --autogenerate -m "Initial migration"

2.	Ensuring that alembic.ini correctly points to script_location = alembic_migrations.
3.	Forcing Alembic to reset its migration state:

alembic stamp head
alembic revision --autogenerate -m "Initial migration"

4.	Running alembic check to detect schema differences.

📌 My Questions:
• Why is Alembic not generating any migration content, even though SQLAlchemy correctly detects the models?
• How can I force Alembic to generate a valid file containing revision and down_revision?
• Could this be caused by a misconfiguration or a known bug in Alembic?

Any help would be greatly appreciated! 🙏🚀

[sifir-gun]

✅ Solution Found: Empty `script.py.mako` File

I found the root cause of this issue. The problem was that my `script.py.mako` file (located in the `alembic_migrations` directory) was empty. This file is crucial as it serves as a template for Alembic to generate migration files.

### How to Fix:

1. Check if your `script.py.mako` is empty:
```bash
cat alembic_migrations/script.py.mako

2. If it's empty, replace its content with the following template:

"""${message}

Revision ID: ${up_revision}
Revises: ${down_revision | comma,n}
Create Date: ${create_date}

"""
from alembic import op
import sqlalchemy as sa
${imports if imports else ""}

# revision identifiers, used by Alembic
revision = ${repr(up_revision)}
down_revision = ${repr(down_revision)}
branch_labels = ${repr(branch_labels)}
depends_on = ${repr(depends_on)}


def upgrade() -> None:
    ${upgrades if upgrades else "pass"}


def downgrade() -> None:
    ${downgrades if downgrades else "pass"}

3. After fixing the template, clean up any failed migrations and try again:

rm -f alembic_migrations/versions/*
alembic stamp head
alembic revision --autogenerate -m "Initial migration"

Why This Works:

• The script.py.mako file is essential for Alembic's migration generation process
• It contains the template that Alembic uses to create new migration files
• Without this template, Alembic can't properly structure the migration files, leading to the "Could not determine revision id from filename" error

As this was my first time using Alembic, I wasn't familiar with all its required files and their purposes. Hope this helps others who are also new to Alembic and encounter the same issue! 🚀

[CaselIT]

alembic init will create a script.py.mako that is not empty. Not sure how you inited your config, but maybe something whet wrong there