Upper lewel SQLAlchemy migration funcitons.
Run migrations in ‘offline’ mode.
This configures the context with just a URL
and not an Engine, though an Engine is acceptable
here as well. By skipping the Engine creation
we don’t even need a DBAPI to be available.
Calls to context.execute() here emit the given string to the
Run migrations in ‘online’ mode.
In this scenario we need to create an Engine
and associate a connection with the context.