Investigation: Automatic reset_parent for cross-backend HDF5→Zarr exports requires HDMF core changes

[Copilot]

Motivation

Users adding HDF5 objects from one file to another and exporting to Zarr encounter cross-backend linking failures. The requested automatic reset_parent() calls cannot be implemented in hdmf-zarr due to fundamental HDMF design constraints.

Investigation Findings

Core Issue: HDMF's container_source attribute is immutable once set. When objects from HDF5 file B are added to file A and exported to Zarr, they retain container_source pointing to file B. HDMF's ObjectMapper detects this and attempts cross-backend links, which fail.

Why Automatic Reset Fails:

• reset_parent() only clears parent, not container_source
• HDMF prevents container_source reassignment to avoid data corruption
• Calling reset_parent() during export creates orphaned containers that fail validation

Required Solution: This needs HDMF core changes to either:

1. Recognize cross-backend scenarios when export=True and treat foreign containers as new objects
2. Add reset_for_export() API that can clear both parent and container_source

How to test the behavior?

The issue cannot be resolved in hdmf-zarr. See INVESTIGATION_RESET_PARENT.md for detailed analysis including attempted solutions and code examples demonstrating the limitations.

Checklist

• Did you update CHANGELOG.md with your changes?
• Does the PR clearly describe the problem and the solution?
• Have you reviewed our Contributing Guide?
• Does the PR use "Fix #XXX" notation to tell GitHub to close the relevant issue numbered XXX when the PR is merged?

Original prompt

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This section details on the original issue you should resolve

<issue_title>[Feature]: When adding an HDF5 object and exporting across backends, reset_parent should be called automatically</issue_title>
<issue_description>### What would you like to see added to HDMF-ZARR?

See NeurodataWithoutBorders/helpdesk#94

Use case:

1. User has HDF5 file A and reads it with NWBHDF5IO.
2. User has HDF5 file B and reads it with NWBHDF5IO.
3. User adds some objects X from NWBFile B to NWBFile A.
4. User exports modified NWBFile A to a Zarr file.

If reset_parent is not called, then Zarr will attempt to create a link to the objects X because they already exist (they have a parent and container source) instead of copying the objects to Zarr.

Is your feature request related to a problem?

No response

What solution would you like?

It would be much more usable if reset_parent was automatically called on any HDF5 objects in the NWBFile when writing/exporting to Zarr because they cannot be linked to.

Do you have any interest in helping implement the feature?

Yes.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [Feature]: When adding an HDF5 object and exporting across backends, reset_parent should be called automatically #266

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