NanmiCoder/MediaCrawler · error · ValueError

Unsupported database type: {db_type}

Error message

Unsupported database type: {db_type}

What it means

ValueError from database/db_session.py get_async_engine when db_type matches none of the supported backends: cached engines, the file-based trio ['json','jsonl','csv'] (which return None), 'sqlite', 'mysql'/'db', or 'postgres'. The string is used both to build the SQLAlchemy async URL and to select the engine, so an unknown value cannot be mapped to a driver.

Source

Thrown at database/db_session.py:70

def get_async_engine(db_type: str = None):
    if db_type is None:
        db_type = config.SAVE_DATA_OPTION

    if db_type in _engines:
        return _engines[db_type]

    if db_type in ["json", "jsonl", "csv"]:
        return None

    if db_type == "sqlite":
        db_url = f"sqlite+aiosqlite:///{sqlite_db_config['db_path']}"
    elif db_type == "mysql" or db_type == "db":
        db_url = f"mysql+asyncmy://{mysql_db_config['user']}:{mysql_db_config['password']}@{mysql_db_config['host']}:{mysql_db_config['port']}/{mysql_db_config['db_name']}"
    elif db_type == "postgres":
        db_url = f"postgresql+asyncpg://{postgres_db_config['user']}:{postgres_db_config['password']}@{postgres_db_config['host']}:{postgres_db_config['port']}/{postgres_db_config['db_name']}"
    else:
        raise ValueError(f"Unsupported database type: {db_type}")

    engine = create_async_engine(db_url, echo=False)
    _engines[db_type] = engine
    return engine


async def create_tables(db_type: str = None):
    if db_type is None:
        db_type = config.SAVE_DATA_OPTION
    await create_database_if_not_exists(db_type)
    engine = get_async_engine(db_type)
    if engine:
        async with engine.begin() as conn:
            await conn.run_sync(Base.metadata.create_all)


@asynccontextmanager
async def get_session() -> AsyncSession:

View on GitHub (pinned to d6f7c5bb90)

Solutions

  1. Set db_type/SAVE_DATA_OPTION to one of the exact literals: 'sqlite', 'mysql' (or 'db'), 'postgres', or 'json'/'jsonl'/'csv'.
  2. For MongoDB use the project's MongoDB store path rather than get_async_engine, which only builds SQL engines.
  3. Use the literal 'postgres', not 'postgresql', for the URL branch to match.
  4. Validate the config value at startup and fail fast with the list of supported types.

Example fix

# before
get_async_engine('postgresql')

# after
get_async_engine('postgres')
Defensive patterns

Strategy: type-guard

Validate before calling

SUPPORTED = {'sqlite', 'mysql', 'db', 'postgres', 'json', 'jsonl', 'csv'}
if db_type not in SUPPORTED:
    raise SystemExit(f'db type must be one of {sorted(SUPPORTED)}, got {db_type!r}')

Type guard

def is_supported_db(t: str) -> bool:
    return isinstance(t, str) and t in {'sqlite', 'mysql', 'db', 'postgres', 'json', 'jsonl', 'csv'}

Try / catch

try:
    engine = get_async_engine(db_type)
except ValueError as e:
    logger.error(f'unsupported db {db_type!r}: {e}')
    raise SystemExit(2)

Prevention

When it happens

Trigger: SAVE_DATA_OPTION / db_type set to a typo ('mongo' is handled elsewhere as a document store but not by this engine function, 'postgresql' instead of 'postgres', 'MySQL' capitalized); passing a backend name that only exists in a different version of the project.

Common situations: Editing SAVE_DATA_OPTION in config/base_config.py; adding a new storage backend without touching db_session; case-sensitive literals ('sqlite' vs 'SQLite') copied from docs.

Related errors

AI-assisted analysis of NanmiCoder/MediaCrawler@d6f7c5bb90 (2026-08-15). Data as JSON: /api/errors/1b99356bfded5b80. Report an issue: GitHub.