 .. 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.


Define an operator extra link
=============================

For each operator, you can define its own extra links that can
redirect users to external systems. The extra link buttons
will be available on the task page:

.. image:: ../img/operator_extra_link.png

The following code shows how to add extra links to an operator:

.. code-block:: python

    from airflow.models.baseoperator import BaseOperator, BaseOperatorLink
    from airflow.utils.decorators import apply_defaults


    class GoogleLink(BaseOperatorLink):
        name = 'Google'

        def get_link(self, operator, dttm):
            return "https://www.google.com"

    class MyFirstOperator(BaseOperator):

        operator_extra_links = (
            GoogleLink(),
        )

        @apply_defaults
        def __init__(self, *args, **kwargs):
            super(MyFirstOperator, self).__init__(*args, **kwargs)

        def execute(self, context):
            self.log.info("Hello World!")

You can also add a global operator extra link that will be available to
all the operators through an airflow plugin. Learn more about it in the
:ref:`plugin example <plugin-example>`.


Add or override Links to Existing Operators
-------------------------------------------

You can also add (or override) an extra link to an existing operators
through an Airflow plugin.

For example, the following Airflow plugin will add an Operator Link on all
tasks using :class:`~airflow.operators.gcs_to_s3.GoogleCloudStorageToS3Operator` operator.

**Adding Operator Links to Existing Operators**
``plugins/extra_link.py``:

.. code-block:: python

  from airflow.plugins_manager import AirflowPlugin
  from airflow.models.baseoperator import BaseOperatorLink
  from airflow.operators.gcs_to_s3 import GoogleCloudStorageToS3Operator

  class S3LogLink(BaseOperatorLink):
      name = 'S3'

      # Add list of all the operators to which you want to add this OperatorLinks
      # Example: operators = [GoogleCloudStorageToS3Operator, GoogleCloudStorageToBigQueryOperator]
      operators = [GoogleCloudStorageToS3Operator]

      def get_link(self, operator, dttm):
          return 'https://s3.amazonaws.com/airflow-logs/{dag_id}/{task_id}/{execution_date}'.format(
              dag_id=operator.dag_id,
              task_id=operator.task_id,
              execution_date=dttm,
          )

  # Defining the plugin class
  class AirflowExtraLinkPlugin(AirflowPlugin):
      name = "extra_link_plugin"
      operator_extra_links = [S3LogLink(), ]


**Overriding Operator Links of Existing Operators**:

It is also possible to replace a built in link on an operator via a Plugin. For example
:class:`~airflow.gcp.operators.bigquery.BigQueryOperator` includes a link to the GCP
console, but if we wanted to change that link we could:

.. code-block:: python

    from airflow.plugins_manager import AirflowPlugin
    from airflow.models.baseoperator import BaseOperatorLink
    from airflow.gcp.operators.bigquery import BigQueryOperator

    # Change from https to http just to display the override
    BIGQUERY_JOB_DETAILS_LINK_FMT = 'http://console.cloud.google.com/bigquery?j={job_id}'


    class BigQueryConsoleLink(BaseOperatorLink):
        """
        Helper class for constructing BigQuery link.
        """
        name = 'BigQuery Console'
        operators = [BigQueryOperator]

        def get_link(self, operator, dttm):
            ti = TaskInstance(task=operator, execution_date=dttm)
            job_id = ti.xcom_pull(task_ids=operator.task_id, key='job_id')
            return BIGQUERY_JOB_DETAILS_LINK_FMT.format(job_id=job_id) if job_id else ''

    # Defining the plugin class
    class AirflowExtraLinkPlugin(AirflowPlugin):
        name = "extra_link_plugin"
        operator_extra_links = [BigQueryConsoleLink(), ]