jroachgolf84 commented on code in PR #67299: URL: https://github.com/apache/airflow/pull/67299#discussion_r3313411850
########## airflow-core/docs/core-concepts/asset-state.rst: ########## @@ -0,0 +1,221 @@ + .. Licensed to the Apache Software Foundation (ASF) under one + or more contributor license agreements. See the NOTICE file + distributed with this work for additional information + regarding copyright ownership. The ASF licenses this file + to you under the Apache License, Version 2.0 (the + "License"); you may not use this file except in compliance + with the License. You may obtain a copy of the License at + + .. http://www.apache.org/licenses/LICENSE-2.0 + + .. Unless required by applicable law or agreed to in writing, + software distributed under the License is distributed on an + "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY + KIND, either express or implied. See the License for the + specific language governing permissions and limitations + under the License. + +.. _concepts:asset-state: + +Asset State +=========== + +.. versionadded:: 3.3 + +Asset state is a persistent key/value store scoped to an *asset*, independent of any particular DAG run. Unlike :doc:`task state </core-concepts/task-state>`, which is tied to a single task instance, asset state persists across runs and is logically owned by the asset itself. It is the natural home for cross-run metadata such as watermarks, incremental-load cursors, and per-asset configuration. + +Asset state is accessed through the task context via ``context["asset_state"]``, or via the ``AssetState`` Task SDK mechanism. + + +When is ``asset_state`` available? +------------------------------------ + +``context["asset_state"]`` is populated for **concrete** :class:`~airflow.sdk.definitions.asset.Asset` inlets and outlets. It is *not* available for :class:`~airflow.sdk.definitions.asset.AssetAlias` inlets. Aliases are resolved at runtime, but asset state accessors are only created for concrete assets declared directly on the task. A task must declare at least one concrete inlet or outlet for ``asset_state`` to contain any entries. + +Asset state is also available using ``AssetState``, provided by the Task SDK. This approach is more commonly used when building ``BaseEventTrigger``'s for things like asset-watching. + +.. warning:: + + **Outlets-only tasks**: if a task declares only ``outlets`` (no ``inlets``), ``context["asset_state"][my_asset]`` may raise a ``KeyError`` at runtime. The workaround is to declare the asset in **both** ``inlets`` and ``outlets``. + + .. code-block:: python + # my_asset defined above ... + + @task(inlets=[my_asset], outlets=[my_asset]) + def write_asset(**context): + context["asset_state"][my_asset].set("watermark", "2024-01-01") + + This known issue will be resolved in a future release. A workaround for this is to use the ``AssetState`` class, provided as part of the Task SDK. More details on that below! Review Comment: From other comment: > outlets are never added to the accessors. The outlets-only KeyError behavior is a consequence of this, not a separate known issue. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
