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https://issues.apache.org/jira/browse/AIRFLOW-3871?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16784208#comment-16784208
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Björn Pollex commented on AIRFLOW-3871:
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Hi, thanks for taking the initiative on this! I think approach #3 is a bit
fragile, for a number of reasons:
* There might be fields I don't want rendered (maybe I use Jinja templating
internally)
* Due to the dynamic nature of Python, I might want to render fields that
can't be found via introspection
I think a viable alternative would be to use the same approach as for operators
- declare which fields need templating using a {{template_fields}} class
variable.
> Allow Jinja templating recursively on object attributes
> -------------------------------------------------------
>
> Key: AIRFLOW-3871
> URL: https://issues.apache.org/jira/browse/AIRFLOW-3871
> Project: Apache Airflow
> Issue Type: Wish
> Components: operators
> Affects Versions: 1.10.0
> Reporter: Galak
> Assignee: Björn Pollex
> Priority: Minor
>
> Some {{Operator}} fields can be templated (using Jinja). Template rendering
> only works for string values (either direct values or values stored in
> collections).
> But a templated string inside a custom class instance won't be rendered
> Here is my scenario:
> I have a python method {{transform_data_file}} which is designed to call a
> command object. This command object constructor
> ({{MyAwesomeDataFileTransformer}}) has parameters that could be templated.
> These templated parameters are not rendered so far (see
> {{BaseOperator.render_template_from_field}} method).
> {code}
> simple_task = PythonOperator(
> task_id='simple_task',
> provide_context=True,
> python_callable=transform_data_file,
> templates_dict={
> 'transformer': MyAwesomeDataFileTransformer(
> "/data/{{ dag.dag_id }}/{{ ts }}/input_file",
> "/data/{{ dag.dag_id }}/{{ ts }}/output_file",
> )
> },
> dag=dag
> )
> {code}
> I have 3 alternatives in mind to allow rendering inner attributes:
> # Either define an Abstract Base Class declaring an abstract method
> {{render_template}}; then my command object would have to extend this
> Abstract Base Class, and then implement {{render_template}} method.
> # Or use duck typing in {{BaseOperator.render_template_from_field}} to call
> {{render_template}} method when it exists on templated custom objects; then
> my command object would just have to implement {{render_template}} method.
> # Or traverse object attributes when rendering templates and call
> {{BaseOperator.render_template}} recursively; then my command object would
> not need any change
> My preferred solution is the 3rd one, but I would like to hear about your
> opinion on this before. Maybe is there a 4th and better solution?
> I would be glad to submit a PR if this functionality is accepted.
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