Taxonomy tag API should return correct data for deeper levels

[jesperhodge]

Screen.Recording.2026-03-17.at.4.23.58.PM.mov

The taxonomy tag API GET, if receiving a full_depth_threshold = 1000, should return taxonomy tags of 4 levels: 0,...,3 (they are zero-indexed).
When a subtag is created for a tag that's at level 2, then the taxonomy tag API should include the new tag in its returned data. Currently it does not.
Creating a subtag at level > 3 (go to a tag at level 3, create new subtag) should return a 4xx error because of the MAX_DEPTH_LEVEL=3 setting on the backend.

Technical Details

To fix the bug, line 538 needs another one of those Q statements for the great grandparent: https://github.com/openedx/openedx-core/blob/848f6633fa4d1c8ede8db90c22a6d4eab485acf9/src/openedx_tagging/models/base.py#L533

When the parent_tag_value is none, the effect otherwise will exclude great-grandchildren.

[bradenmacdonald]

The taxonomy tag API GET, if receiving a full_depth_threshold = 1000, should return taxonomy tags of 4 levels: 0,...,3 (they are zero-indexed).
When a subtag is created for a tag that's at level 2, then the taxonomy tag API should include the new tag in its returned data. Currently it does not.
Creating a subtag at level > 3 (go to a tag at level 3, create new subtag) should return a 4xx error because of the MAX_DEPTH_LEVEL=3 setting on the backend.

I think we need to clear up the documentation here. I don't think TAXONOMY_MAX_DEPTH=3 means "we allow taxonomies up to 4 levels deep". I think as actually implemented it means "bulk APIs only work for tags up to 3 levels deep (Root->Child->Grandchild), but we technically allow tags of unlimited depth". See openedx/openedx-core#509 for my attempt to clarify this.

[bradenmacdonald]

Actually I have a better fix in progress here: openedx/openedx-core#510

[jesperhodge]

Hi @bradenmacdonald ,

I think before we just merge one fix or another for the backend, we need to clarify what is going on and what the actual requirements are.

I did a full analysis of this issue. Before we go further, could you have a look at openedx/openedx-core#507 (comment) ? If you don't agree with something in there, let's discuss it.

We should align on the requirements before we merge any backend changes.

[bradenmacdonald]

@jesperhodge The change I'd like to use is the new PR that I opened here: openedx/openedx-core#510

It basically removes any technical restrictions on depth, so all the APIs support arbitrary depth, and then once that's all working internally, it will include an absolute depth limit in the import/create APIs, to limit taxonomies to 3-5 levels - whatever the product team thinks is a good limit. I don't see any downside to this approach, do you?