docs: [FC-0074] add docs about creating new filters with pipeline steps

[mariajgrimaldi]

Description

Update how-to documents to create and implement pipeline steps considering design suggestions introduced in #240.

Here are the main documents to review:

• How to Create a New Filter with Long-Term Support: https://github.com/openedx/openedx-filters/pull/242/files#diff-2825244e325626bcad68d204d59aa3e6ff696d1b5043fd4b990bd77e88dbb9a1
• Implement Pipeline Steps: https://github.com/openedx/openedx-filters/pull/242/files#diff-f1e167403e1377f568c3a2641fb3a151cd61d26887b3a468f91669d4494aee61

Testing instructions

You can review the docs here: https://docsopenedxorg--242.org.readthedocs.build/projects/openedx-filters/en/242/how-tos/index.html

Deadline

None

Checklists

Check off if complete or not applicable:

Merge Checklist:

• All reviewers approved
• Reviewer tested the code following the testing instructions
• CI build is green
• Version bumped
• Changelog record added with short description of the change and current date
• Documentation updated (not only docstrings)
• Code dependencies reviewed
• Fixup commits are squashed away
• Unit tests added/updated
• Noted any: Concerns, dependencies, migration issues, deadlines, tickets

Post Merge:

• Create a tag
• Create a release on GitHub
• Check new version is pushed to PyPI after tag-triggered build is
  finished.
• Delete working branch (if not needed anymore)
• Upgrade the package in the Open edX platform requirements (if applicable)

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[MaferMazu]

I have one suggestion, but the rest looks good to me.

Thanks @mariajgrimaldi ✨

[MaferMazu]

Thanks for addressing my feedback. This looks good to me ✅

[felipemontoya]

Some inline comments. Overall looks good, but I'm starting to see something that we are doing rather unintentionally. By focusing our documentation effort on all the parts of the lifecycle of : creating a new filter that did not previously exist, add said filter to the platform, implement pipeline steps with your feature, we are creating the impression on devs that they all need to take this route. I think we need to make it very well known that there are already quite a few filters and events available and that for every one of those you only need the part where you develop your code. This misconception is pushing people to believe that using filters is too complicated and not worth doing.

[felipemontoya]

Suggested change

I want to add a filter that will be triggered when a user enrolls in a course from the course about page. This filter will be used to prfilter users from enrolling in a course if they do not meet the eligibility criteria. The filter will be triggered when the user clicks the enroll button on the course about page and will check if the user meets the eligibility criteria. If the user does not meet the criteria, the filter will raise an exception to prfilter the user from enrolling in the course.

I want to add a filter that will be triggered when a user enrolls in a course from the course about page. This filter will be used to prevent users from enrolling in a course if they do not meet the eligibility criteria. The filter will be triggered when the user clicks the enroll button on the course about page and will check if the user meets the eligibility criteria. If the user does not meet the criteria, the filter will raise an exception to prevent the user from enrolling in the course.

[mariajgrimaldi]

Thank you for noticing!

[felipemontoya]

I think we should say here that the pipeline steps are meant to be written in the plugin code and not in the openedx-filters library.

[mariajgrimaldi]

There is a note about it here: https://github.com/openedx/openedx-filters/pull/242/files#diff-f1e167403e1377f568c3a2641fb3a151cd61d26887b3a468f91669d4494aee61R57. But I agree adding it here could make it clearer.

[felipemontoya]

openedx-filters plugin -> openedx-filters library. To not make it more confusing plugin should refer always to the developer's pluggable code and the openedx-filters or openedx-events should be called the library.

[felipemontoya]

"so the library's environment recognizes the event you want to consume" this is also confusing. We are not consuming an event, but creating a filter pipeline in this guide.

[mariajgrimaldi]

I borrowed this from the consume events docs, that's why it is all mixed up. Thank you for noticing! Although I now have a question, technically openedx-events is a plugin, do you think that would cause misunderstandings? Calling openedx-events a plugin instead?

[felipemontoya]

What threshold do you use to recognize something as a plugin? For me the defining characteristic of a plugin, is that it defines the plugin_app in its apps.py config. Neither events nor filters do that. That is why I call them libraries.

I could certainly be picking the wrong definition here. The other approach that I use for this, which is what triggered the comment, is that plugin is something that is not part of the core. We try to gently push developers in the direction of using plugins for the custom development instead of forking. By this approach also events and filters would not be considered plugins.

[mariajgrimaldi]

Sorry for the misunderstanding. opened-events is a Django application, which makes it more than a library -- in my humble opinion, at least. I thought it actually defined a plugin_app, but after reviewing apps.py I realized it didn't.

[mariajgrimaldi]

Thank you, @felipemontoya, for the thorough review.

Overall looks good, but I'm starting to see something that we are doing rather unintentionally. By focusing our documentation effort on all the parts of the lifecycle of : creating a new filter that did not previously exist, add said filter to the platform, implement pipeline steps with your feature, we are creating the impression on devs that they all need to take this route. I think we need to make it very well known that there are already quite a few filters and events available and that for every one of those you only need the part where you develop your code.

I hear what you're saying, but I'm not sure I follow, given that one of the first steps in creating a pipeline specifically mentions reviewing the list of available filters to identify the right one for the use case: https://docsopenedxorg--242.org.readthedocs.build/projects/openedx-filters/en/242/how-tos/create-a-pipeline-step.html#step-1-understand-your-use-case-and-identify-the-filter-to-use. Do you think that part isn't clear enough? I’m open to suggestions to make it more obvious.

Maybe a note at the beginning of creating a new filter warning devs that they don't need to create one if there's already one that fits their use case.

[mariajgrimaldi]

@felipemontoya: I've addressed all your comments in this commit 2ee41e3. Thank you again!

[felipemontoya]

Thanks @mariajgrimaldi I think the note makes it clear that this is not the first step, but one that must be taken only when there is no similar available filter.