Load included and related serializers in meta class

[SafaAlfulaij]

Fixes #858

Description of the Change

As mentioned in the issue, this caches included_serializers and related_serializers in the dictionary to ease the process of retrieving in various places.
This approach is also used by DRF for binding fields: https://github.com/encode/django-rest-framework/blob/71e6c30034a1dd35a39ca74f86c371713e762c79/rest_framework/utils/serializer_helpers.py#L137

Checklist

• PR only contains one change (considered splitting up PR)
• unit-test added updated
• documentation updated
• CHANGELOG.md updated (only for user relevant changes)
• author name in AUTHORS

[codecov]

Codecov Report

Merging #926 (c863a3d) into master (684063b) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #926   +/-   ##
=======================================
  Coverage   96.81%   96.82%           
=======================================
  Files          65       65           
  Lines        3894     3904   +10     
=======================================
+ Hits         3770     3780   +10     
  Misses        124      124           

Impacted Files	Coverage Δ
rest_framework_json_api/relations.py	88.46% <100.00%> (ø)
rest_framework_json_api/renderers.py	90.15% <100.00%> (ø)
rest_framework_json_api/schemas/openapi.py	98.64% <100.00%> (+0.42%)	⬆️
tests/test_serializers.py	100.00% <100.00%> (ø)
example/utils.py	92.36% <0.00%> (-0.20%)	⬇️
example/views.py	94.21% <0.00%> (-0.08%)	⬇️
example/tests/test_serializers.py
example/serializers.py	89.14% <0.00%> (+1.06%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 684063b...c863a3d. Read the comment docs.

[sliverc]

Thanks for working on this. See my inline comments and do not forget to write a changelog entry.

[SafaAlfulaij]

Changes done.
But I'm not sure what to do with "self" and inline self-related serializers.

[SafaAlfulaij]

Ping?

[sliverc]

I haven't forgotten about this PR but haven't really had time to look at it closely.

Seems some comments were not addressed but somehow through outdating were resolved by GitHub directly. So I moved those comment to the right code line.

Sorry if this has caused lots of notifications. The conversations which are still open are the issues which still need to be addressed. Thanks.

[SafaAlfulaij]

I'm sorry but I can't work on this anymore. I tried an approach where I set included_serializers and related_serializers to None if not provided, but it resulted in a bit more complicated code, you'll find it before applying the commit "Simplify caching included serializers".

[sliverc]

@SafaAlfulaij Thanks for having worked on this. I made the last minor changes and this PR should be ready now and be merged once CI is green.

[jarekwg]

@sliverc this is a pretty neat performance boost, what's the plan for the next release?

[sliverc]

@jarekwg I would not overestimate this change in terms of performance because it's just few imports less. This is mainly a API cleanup so included serializers can be simply retrieved by serializer.included_serializers instead of a utility method.
In terms of next release I assume we will do one once Django 4.0 is released (according to release notes expected in December).

[auvipy]

besides django 4.0 compat new release is needed in drf as well.