Skip to main content

Contexts

DBOS provides a number of useful context methods and variables. All are accessed through the syntax DBOS.<method> and can only be used once a DBOS class object has been initialized.

Context Methods​

send​

DBOS.send(
    destination_id: str,
    message: Any,
    topic: Optional[str] = None
) -> None

Send a message to the workflow identified by destination_id. Messages can optionally be associated with a topic.

Parameters:

  • destination_id: The workflow to which to send the message.
  • message: The message to send. Must be serializable.
  • topic: A topic with which to associate the message. Messages are enqueued per-topic on the receiver.

recv​

DBOS.recv(
    topic: Optional[str] = None,
    timeout_seconds: float = 60,
) -> Any

Receive and return a message sent to this workflow. Can only be called from within a workflow. Messages are dequeued first-in, first-out from a queue associated with the topic. Calls to recv wait for the next message in the queue, returning None if the wait times out. If no topic is specified, recv can only access messages sent without a topic.

Parameters:

  • topic: A topic queue on which to wait.
  • timeout_seconds: A timeout in seconds. If the wait times out, return None.

Returns:

  • The first message enqueued on the input topic, or None if the wait times out.

set_event​

DBOS.set_event(
    key: str,
    value: Any,
) -> None

Create and associate with this workflow an immutable event with key key and value value. Can only be called from within a workflow. Events are immutable and attempting to emit an event twice from a given workflow instance will error.

Parameters:

  • key: The key of the event.
  • value: The value of the event. Must be serializable.

get_event​

DBOS.get_event(
    workflow_id: str,
    key: str,
    timeout_seconds: float = 60,
) -> None

Retrieve an event published by the workflow identified by workflow_id to the key key. Waits for the event to be published, returning None if the wait times out.

Parameters:

  • workflow_id: The identifier of the workflow whose events to retrieve.
  • key: The key of the event to retrieve.
  • timeout_seconds: A timeout in seconds. If the wait times out, return None.

Returns:

  • The value of the event published by workflow_id with name key, or None if the wait times out.

sleep​

DBOS.sleep(
    seconds: float
) -> None

Sleep for the given number of seconds. May only be called from within a workflow. This sleep is durable—it records its intended wake-up time in the database so if it is interrupted and recovers, it still wakes up at the intended time.

Parameters:

  • seconds: The number of seconds to sleep.

retrieve_workflow​

DBOS.retrieve_workflow(
    workflow_id: str,
    existing_workflow: bool = True,
) -> WorkflowHandle[R]

Retrieve the handle of a workflow with identity workflow_id.

Parameters:

  • workflow_id: The identifier of the workflow whose handle to retrieve.
  • existing_workflow: Whether to throw an exception if the workflow does not yet exist, or to wait for its creation. If set to False and the workflow does not exist, will wait for the workflow to be created, then return its handle.

Returns:

  • The handle of the workflow whose ID is workflow_id.

start_workflow​

DBOS.start_workflow(
    func: Workflow[P, R],
    *args: P.args,
    **kwargs: P.kwargs,
) -> WorkflowHandle[R]

Start a workflow in the background and return a handle to it. The DBOS.start_workflow method resolves after the handle is durably created; at this point the workflow is guaranteed to run to completion even if the app is interrupted.

Example syntax:

@DBOS.workflow()
def example_workflow(var1: str, var2: str):
    DBOS.logger.info("I am a workflow")

# Start example_workflow in the background
handle: WorkflowHandle = DBOS.start_workflow(example_workflow, "var1", "var2")

Context Variables​

logger​

DBOS.logger: Logger

Retrieve the DBOS logger. This is a pre-configured Python logger provided as a convenience.

sql_session​

DBOS.sql_session: sqlalchemy.Session

May only be accessed from within a transaction. Retrieves the SQLAlchemy session of the transaction, a database connection the transaction can use to interact with the database.

workflow_id​

DBOS.workflow_id: str

May only be accessed from within a workflow, step, or transaction. Return the identity of the current workflow.

span​

DBOS.span: opentelemetry.trace.Span

Retrieve the OpenTelemetry span associated with the curent request. You can use this to set custom attributes in your span.

request​

DBOS.request: Request

May only be accessed from within the handler of a FastAPI request, or in a function called from the handler. Retrieve request information parsed from FastAPI:

headers: Headers # The request headers
path_params: dict[str, Any] # The request's path parameters
query_params QueryParams # The request's query parameters
url: URL # The URL to which the request was sent
base_url: URL # The base URL of the request
client: Optional[Address] # Information about the client that sent the request
cookies: dict[str, str] # The request's cookie parameters
method: str # The HTTP method of the request

config​

DBOS.config: ConfigFile

Return the current DBOS configuration, as a ConfigFile.

Authentication​

authenticated_user​

DBOS.authenticated_user: Optional[str]

Return the current authenticated user, if any, associated with the current context.

authenticated_roles​

DBOS.authenticated_roles: Optional[List[str]]

Return the roles granted to the current authenticated user, if any, associated with the current context.

assumed_role​

DBOS.assumed_role: Optional[str]

Return the role currently assumed by the authenticated user, if any, associated with the current context.

set_authentication​

DBOS.set_authentication(
  authenticated_user: Optional[str],
  authenticated_roles: Optional[List[str]]
) -> None

Set the current authenticated user and granted roles into the current context. This would generally be done by HTTP middleware

Context Management​

SetWorkflowID​

SetWorkflowID(
    wfid: str
)

Set the workflow ID/idempotency key of the next workflow to run. Should be used in a with statement.

Example syntax:

@DBOS.workflow()
def example_workflow():
    DBOS.logger.info(f"I am a workflow with ID {DBOS.workflow_id}")

# The workflow will run with the supplied ID
with SetWorkflowID("very-unique-id"):
    example_workflow()

DBOSContextEnsure​

DBOSContextEnsure()

  with DBOSContextEnsure():
    # Call DBOS functions
    pass

Use of DBOSContextEnsure ensures that there is a DBOS context associated with the enclosed code prior to calling DBOS functions. DBOSContextEnsure is generally not used by applications directly, but used by event dispatchers, HTTP server middleware, etc., to set up the DBOS context prior to entry into function calls.