Setting model metadata manually after database connection

[ghost]

In the example code, all the Meta inner class have a database class variable that is set during the class definition.

How to delay the setting of this field until I actually have created a Database object (via database.Database(db_url))?

Setting it to None and then manually updating it for each model (which is not super nice either) after a database conn has been established doesn't work since if we import the model class, ormar immediately raises an exception

fk_string = to.Meta.tablename + "." + to.get_column_alias(to.Meta.pkname)
TypeError: unsupported operand type(s) for +: 'NoneType' and 'str'

[ghost]

Answering own question

It seems model classes can be defined without issue containing a database object in the meta class that hasn't been connected to yet. So we can connect later. This thread can be closed.

[NiklasRosenstein]

I have the same question but I don't know the database URL string in advance. Is there a clean way to create an uninitialized database and setting the URL connection string later?

What I do now is quiet a nasty workaround, something akin to

async def main():
  config = load_config_from_disk()
  # Need to set DATABASE_URL so it can be read in db.py to pass to the database object.
  os.environ["DATABASE_URL"] = config.database_url
  # Now import the database module.
  from . import db
  # ...

And in db.py

class BaseMeta(ormar.ModelMeta):
    database_url = os.environ["DATABASE_URL"]
    database = databases.Database(database_url)
    metadata = sqlalchemy.MetaData()