main.py

import logging
from alembic import context
from sqlalchemy import create_engine

config = context.config
logger = logging.getLogger("alembic.env")


def get_engine():
    """Creates an engine based on Alembic config."""
    db_url = config.get_main_option("sqlalchemy.url")
    if not db_url:
        logger.error("No database URL found in Alembic config.")
        raise RuntimeError("Database URL missing")
    return create_engine(db_url)


def run_migrations():
    """Executes migrations in online mode."""
    engine = get_engine()
    with engine.connect() as connection:
        context.configure(connection=connection, target_metadata=None)
        with context.begin_transaction():
            context.run_migrations()


if context.is_offline_mode():
    context.configure(url=config.get_main_option("sqlalchemy.url"))
    with context.begin_transaction():
        context.run_migrations()
else:
    run_migrations()