Fix DisplayOptions Serializer to validate display options when updating a column

[silentninja]

Related to #1228

When a column is partially updated with an invalid display option, it does not get validated and the request succeeds due to weird behaviour with the DRF serializer which treats nested data as a partial update too, but we completely replace the display options object when saving it, so we end up with a scenario where a required field could be missing. So when the same object is requested by the API, the serializer throws up an error when looking up for the required field in the display options JSON object. This PR fixes it by validating display options during a partial update

Technical Details

During a partial update of a parent serializer, drf calls the nested serializer with partial flag even if we haven't explicitly specified it. We consider update to display options as a full update but since DRF takes a partial flag from the parent serializer, the nested display options serializer gets treated as a partial update, so the serializer becomes valid even if a required field is missing. A mixin was used to fix the behaviour for the individual display options serializer but it wasn't applied to the mapping serializer. This PR adds the mixin that fixes the behaviour of the DRF serializer to the mapping serializer.

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[silentninja]

@pavish This PR adds validation for display options when partially updating a column serializer. Based on the sample requests you had mentioned in issue #1228, I am assuming you would be sending empty object even if the column type has the required display options. Can you open a separate PR to address the issue?

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Codecov Report

Merging #1297 (4336a9b) into master (b68e6de) will increase coverage by 0.15%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1297      +/-   ##
==========================================
+ Coverage   93.49%   93.65%   +0.15%     
==========================================
  Files         114      114              
  Lines        4426     4426              
==========================================
+ Hits         4138     4145       +7     
+ Misses        288      281       -7     

Flag	Coverage Δ
pytest-backend	93.65% <ø> (+0.15%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
mathesar/api/serializers/shared_serializers.py	87.67% <ø> (+9.58%)	⬆️

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[pavish]

@silentninja

I am assuming you would be sending empty object even if the column type has the required display options

I do not understand this. While patching a column, I'd send an empty object if the user has not set any display options even if the column allows display options and has required ones. See Kriti's comment here.

Based on the sample requests you had mentioned in issue #1228

Also the sample requests mentioned in #1228 contain values for all the required fields.

[silentninja]

Also the sample requests mentioned in #1228 contain values for all the required fields.

Sorry got confused with issue #1276 scenario 2, please ignore that message. But this PR should solve the invalid state, so now it has to be None or a valid object at the time of validation. I have added a comment to #1276 on how to deal with an empty object.

[mathemancer]

While I do think this change is needed, and the test looks good, I don't understand how this PR fixes #1228 . Can you add some explanation about that to the description for posterity?

[silentninja]

@mathemancer #1228 happens due to a bugs that can lead to invalid data being saved, this PR fixes one of the bugs that can cause the error. I updated the description to mention it is related to #1228 rather being a complete fix. I have also updated the description to mention the cause of the issue and how this PR aims to solve it.

[mathemancer]

Okay, thanks for the extra explanation.