Fix constraints endpoint's error behaviour

[Anish9901]

Fixes #1030

This PR Fixes many small unhandled exceptions and 500s caused by the constraints API endpoint.

Technical details

• An empty columns array:

{"type":"unique","columns":[]}

• Response:

{
    "code": 4005,
    "message": "Columns field cannot be empty.",
    "field": null,
    "detail": null
}

• Invalid "type"

{"type":"foo","columns":[1]}

• Response:

{
    "code": 4005,
    "message": "Unknown type passed.",
    "field": null,
    "detail": null
}

Checklist

• [x] My pull request has a descriptive title (not a vague title like Update index.md).
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• [ ] I added tests for the changes I made (if applicable).
• [ ] I added or updated documentation (if applicable).
• [x] I tried running the project locally and verified that there are no visible errors.

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[codecov-commenter]

Codecov Report

Merging #1406 (0e43557) into master (f704629) will decrease coverage by 0.05%. The diff coverage is 72.72%.

@@            Coverage Diff             @@
##           master    #1406      +/-   ##
==========================================
- Coverage   92.26%   92.20%   -0.06%     
==========================================
  Files         139      139              
  Lines        6051     6071      +20     
==========================================
+ Hits         5583     5598      +15     
- Misses        468      473       +5     

Flag	Coverage Δ
pytest-backend	92.20% <72.72%> (-0.06%)	:arrow_down:

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

Impacted Files	Coverage Δ
mathesar/api/serializers/constraints.py	92.04% <71.42%> (-5.06%)	:arrow_down:
mathesar/api/db/viewsets/constraints.py	86.66% <100.00%> (+0.45%)	:arrow_up:

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[Anish9901]

@silentninja I am getting a KeyError while sending this request:

{"type":"unique","columns":[9999]}

I suspect the error is generated by this part of the code https://github.com/centerofci/mathesar/blob/4ccea635e390732823f1294811d6a623ab864043/mathesar/api/serializers/shared_serializers.py#L116-L118 How can I solve this error?

[silentninja]

@silentninja I am getting a KeyError while sending this request:

{"type":"unique","columns":[9999]}

The actual error is from this line

https://github.com/centerofci/mathesar/blob/4716b0fb999b164a7354ad52dc4bb985e7481bfc/mathesar/api/exceptions/mixins.py#L64

The column id 999 does not exist and the queryset throws up an error correctly but when it gets passed to the error handling mixin, it gets handled incorrectly. You would need to fix the error handling mixin to convert ManyRelatedField type errors correctly

[Anish9901]

I noticed that you are not using the correct error class when throwing up an error. Each error type should also have a unique error code so that the frontend can use the code to figure out the error that is thrown

Actually, the mathesar.api.exceptions.validation_exceptions module was not added to the codebase while I worked on this issue hence the wrong error class. Sorry for the delay.

[Anish9901]

@silentninja I am also thinking of fixing the following bugs in a later PR as they are very closely related and I haven't figured out how to handle the KeyError yet. I am changing the PR description accordingly.

• Non-existent column id, e.g.:

  {"type":"unique","columns":[9999]}
  

and

• Attempting to set a unique constraint by supplying the id of a column that exists in a different table from the table whose id is supplied in the URL.

[silentninja]

I am also thinking of fixing the following bugs in a later PR as they are very closely related and I haven't figured out how to handle the https://github.com/centerofci/mathesar/pull/1406#issuecomment-1198305111 yet

Okay cool, just create an issue for it before you start working on it so that I can point you to the source of the problem.

[Anish9901]

Ah, it didn't occur to me that I should define specific exception classes instead of already written once.

[silentninja]

Thanks for the PR @Anish9901, I made some changes to error classes as it was a small fix and merged the PR.