Remove the deferred FK validation API and unused backend bulk helpers #396

❌ This issue is not open for contribution. Visit Contributing guidelines to learn about the contributing process and how to find suitable issues.

Overview

Remove the deferred FK validation API and the backend bulk-write helpers that no Morango code calls after the streaming deserialization migration.

Background & Motivation

#392 replaced legacy deserialization with the streaming pipeline in morango/sync/stream/deserialize.py. The removed legacy code was the only caller of the following. Each one now has no caller in Morango outside its own definition and tests:

The design spec for #392 kept them on purpose, to keep the SyncableModel API stable in that PR. A search of learningequality/kolibri (develop) finds no use of any of them. The one _bulk_update match, in kolibri/core/attendance/test/test_api.py, is unrelated to these backend helpers.

User Story / Use Case

As a Morango maintainer,
I want the code that the deserialization path no longer uses to be gone,
So that readers do not mistake it for a live code path, and we do not maintain it for each database backend.

Description & Expected Outcomes

• The five items above no longer exist, and neither do the tests that only exercise them.
• Imports that only these items used are removed.
• The 0.9.0 section of CHANGELOG.md lists each removed public name, like the other removals in that release.

If you find a caller that we missed, keep that item and record the reason in the PR.

Value Add & Impact

• Less dead code in the sync backends. The backends hold SQL for each database, which makes unused code there costly to read and to change.
• deferred_clean_fields no longer suggests a supported way to validate FKs that nothing in Morango uses.

Deliverables & Contracts

• Remove SyncableModel.deferred_clean_fields and ForeignKeyReference.
• Remove TemporaryTable.
• Remove _bulk_full_record_upsert and _bulk_update from the base, PostgreSQL and SQLite backends.
• Add the removals to the 0.9.0 changelog.

Acceptance Criteria

• A search of morango/ and tests/ finds none of the five names.
• CHANGELOG.md lists the removals under 0.9.0.
• make test passes on SQLite and PostgreSQL.
• prek run --all-files passes.

Technical Pointers & Architecture

• Target Components / Context: morango/models/core.py, morango/sync/backends/.
• Related Patterns: Streaming deserialization part 3: sink #392 removed the legacy deserialization path in the same way, with changelog entries under 0.9.0.
• Data Model & Schema Considerations: None. No model fields or migrations change.
• Resilience & Failure Modes: None at runtime, since nothing calls this code.

Notes & Tradeoffs

• Dependencies: Blocked by Streaming deserialization part 3: sink #392. Do this before 0.9.0 ships, so that all the removals land in one release.
• Related: Lint and format the files excluded from ruff #394. morango/sync/backends/postgres.py and sqlite.py are excluded from ruff, so the hooks will not flag imports that become unused there. Check those files by hand.
• Testing Requirements: Run the full suite on both databases, because the backend helpers differ for each database.
• Tradeoffs & Alternatives Considered: Keeping the items for external callers was considered. No Kolibri use exists, and 0.9.0 already removes other private deserialization APIs.

Metadata

Complexity: Low
Target Branch: release-v0.9.x
Labels: TAG: tech update / debt

AI Usage

Drafted with Claude Code from review feedback on #392. Claude searched Morango for the remaining callers of each item, and searched Kolibri on GitHub for external use. I chose to track this as a separate issue instead of expanding #392.