Add wiki documentation about index.yaml

[seanlip]

Having the correct indices in the index.yaml file is a prerequisite for deployment, but the update flow for this file is unlikely to be clear to new contributors. It's detailed here: https://cloud.google.com/appengine/docs/flexible/configuring-datastore-indexes-with-index-yaml?tab=python

This can result in contributors getting edits in their index.yaml file that they didn't put there, and not knowing what to do with them. We don't seem to mention this gotcha at all in the wiki. Perhaps we should add an index.yaml page in the developer reference in the sidebar so that if a contributor runs into this issue they have some idea of what to do. (See e.g. oppia/oppia#17742 for an example of this happening in practice.)

Ideally, the wiki page would explain:

• what index.yaml is and what it's used for
• what sorts of datastore queries will require updates to index.yaml, and which don't
• what developers should do in index.yaml when adding a new multi-field datastore query

Note: When writing this page, please ensure that you test the flows locally by trying out appropriate changes on the oppia/oppia repo. If you'd like to take this issue up, explain in your comment what the instructions for the last two points above are, and how you verified those instructions.

[KunjMaheshwari]

Please assign this issue to me @seanlip @U8NWXD @jahd2602 .

[seanlip]

@KunjMaheshwari Per the guidance at https://github.com/oppia/oppia/wiki/Contributing-code-to-Oppia#choosing-a-good-first-issue, please provide an explanation of what your PR will do (with names of files you're changing, what you plan to change in each file, etc.). If it looks good, we can assign you to this issue.

Please also follow the other instructions on that wiki page if you have not yet done so. Thanks!

[vaishnavi192]

Hey @seanlip I want to work on this issue. So, I created a new index.yaml file in the codebase in workflows section however I am not sure where do we have to create this file? Can you plz tell. I did the following additions. Have a look. If these are fine then kindly assign me this issue. I will create a PR today itself

[seanlip]

Hi @vaishnavi192, I think you might be misinterpreting the issue. The index.yaml file is a file that's used by Google App Engine to manage datastore indexes. The aim of this issue is to create a wiki page explaining to developers how to use it.

If you are not familiar with index.yaml in Google App Engine then I would suggest not taking up this issue. Thanks!

[jaugust4]

Index.yaml-Explanation.md

Here is my first attempt at documentation for index.yaml. Let me know if there is anything else I need to add. My plan for PR is to add this file to the oppia-web-developer-docs repository. Let me know if any further steps are needed.