Create database if not exists.

hi there -

Alembic doesn’t do anything with “CREATE DATABASE”, that part is normally run by the database administrator manually, or as part of your software install / build system if you are using something like that (e.g. ansible, docker, puppet, shell scripts, etc).

you can also add this step to your env.py if you’d like, basically as env.py runs through engines, you can emit "CREATE DATABASE " based on what the URL says it should be. you can parse the url using sqlalchemy.engine.url.make_url(url_string) then look at the “database” portion (if this is mysql or postgresql) and emit CREATE DATABASE from that given your “master” database connection.

I ended up doing this which worked.

    for name in re.split(r",\s*", db_names):
        engines[name] = rec = {}
        rec["engine"] = engine = engine_from_config(
            context.config.get_section(name),
            prefix="sqlalchemy.",
            poolclass=pool.NullPool,
        )

        host_uri = re.sub(name + r"$", '', str(engine.url))
        if host_uri not in host_connections:
            host_connections[host_uri] = []

        host_connections[host_uri].append(name)

    for host, databases in host_connections.items():
        engine = create_engine(host)
        conn = engine.connect()
        try:
            for database in databases:
                logger.info(
                    "Ensuring database '%s' exists on host '%s'" % (database, host))
                    conn.execute("CREATE DATABASE IF NOT EXISTS %s" % database)
        except Exception as ex:
            logger.error(ex)
        finally:
            conn.close()

The only nice to have feature I’m missing is supressing the warning if the database already exists.