Tests and Migrations
Databases is designed to allow you to fully integrate with production ready services, with API support for test isolation, and integration with Alembic for database migrations.
For strict test isolation you will always want to rollback the test database to a clean state between each test case:
database = Database(DATABASE_URL, force_rollback=True)
This will ensure that all database connections are run within a transaction that rollbacks once the database is disconnected.
If you're integrating against a web framework you'll typically want to use something like the following pattern:
if TESTING: database = Database(TEST_DATABASE_URL, force_rollback=True) else: database = Database(DATABASE_URL)
This will give you test cases that run against a different database to the development database, with strict test isolation so long as you make sure to connect and disconnect to the database between test cases.
For a lower level API you can explicitly create force-rollback transactions:
async with database.transaction(force_rollback=True): ...
databases uses SQLAlchemy core, you can integrate with Alembic
for database migration support.
$ pip install alembic $ alembic init migrations
You'll want to set things up so that Alembic references the configured
DATABASE_URL, and uses your table metadata.
alembic.ini remove the following line:
sqlalchemy.url = driver://user:pass@localhost/dbname
migrations/env.py, you need to set the
'sqlalchemy.url' configuration key,
target_metadata variable. You'll want something like this:
# The Alembic Config object. config = context.config # Configure Alembic to use our DATABASE_URL and our table definitions. # These are just examples - the exact setup will depend on whatever # framework you're integrating against. from myapp.settings import DATABASE_URL from myapp.tables import metadata config.set_main_option('sqlalchemy.url', str(DATABASE_URL)) target_metadata = metadata ...
Note that migrations will use a standard synchronous database driver,
rather than using the async drivers that
databases provides support for.
This will also be the case if you're using SQLAlchemy's standard tooling, such
metadata.create_all(engine) to setup the database tables.
Note for MySQL:
For MySQL you'll probably need to explicitly specify the
pymysql dialect when
using Alembic since the default MySQL dialect does not support Python 3.
If you're using the
databases.DatabaseURL datatype, you can obtain this using