fix: Issue when delete all tags on import [FC-0036]

[ChrisChV]

Description

This fix an error when it comes to performing actions on a taxonomy with tags that have external_id=None

More info

Part of: openedx/modular-learning#126

Testing instructions

Please ensure that the tests cover the expected behavior

After merge

• Create a tag to upload the new version

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[rpenido]

Because of this change, I think we also need to change the code below:
https://github.com/openedx/openedx-learning/blob/fb8d16112fa4705fda8f8ac44cd3401cfb08619e/openedx_tagging/core/tagging/import_export/import_plan.py#L96

Context: this is to prevent updating a tag that could already be deleted

The following test (to be put in import_export/test_api.py) reproduce the issue:

    def test_import_removing_with_childs_no_external_id(self) -> None:
        """
        Test import need to remove childs with parents that will also be removed,
        using tags without external_id
        """
        new_taxonomy = Taxonomy(name="New taxonomy")
        new_taxonomy.save()
        level2 = Tag.objects.create(
            id=1000,
            value="Tag 2",
            taxonomy=new_taxonomy,
        )
        level1 = Tag.objects.create(
            id=1001,
            value="Tag 1",
            taxonomy=new_taxonomy,
        )
        level3 = Tag.objects.create(
            id=1002,
            value="Tag 3",
            taxonomy=new_taxonomy,
        )
        level2.parent = level1
        level2.save()

        level3.parent = level3
        level3.save()

        # Import with empty tags, to remove all tags
        importFile = BytesIO(json.dumps({"tags": []}).encode())
        result, _tasks, _plan =  import_export_api.import_tags(
            new_taxonomy,
            importFile,
            ParserFormat.JSON,
            replace=True,
        )
        assert result

[ChrisChV]

Good catch! Thanks!

[ChrisChV]

@rpenido Updated here: b1c4cc9

[ChrisChV]

@rpenido It's ready for another review

[rpenido]

LGTM @ChrisChV! 👍

• I read through the code
• I checkout the branch and run the tests
• I imported tags over a Taxonomy that originated this bug

@ormsbee If you have time, could you please review/merge this PR while @bradenmacdonald is off?

Thank you!

[ormsbee]

@rpenido: I'm also technically off until Jan 2. Is this blocking your work?

[rpenido]

@rpenido: I'm also technically off until Jan 2. Is this blocking your work?

No @ormsbee. This is not urgent and could wait. Sorry to bother you!

Thank you for your response and have a good holiday! 😃

[ChrisChV]

@bradenmacdonald It's ready for another review

[bradenmacdonald]

Almost ready to merge. Just some stray print calls. Thanks.

[bradenmacdonald]

From a user perspective, it's confusing that this sometimes says <TagItem> and other times says <Tag>. We may need to tweak this in the future, especially if we're trying to display this nicely in the frontend. (Though maybe we also need a JSON version of the plan for that.) I think this is OK for now though.

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