Summary

Closes #3708

Metadata-only updates (e.g. session ID changes at mem0/memory/main.py:670 and :1761) call vector_store.update(vector_id=..., vector=None, payload=...). This crashes on Milvus (DataNotMatchException — Milvus requires a valid float vector for every upsert) and Qdrant (ValidationError — PointStruct rejects vector=None).

Problem

Milvus (mem0/vector_stores/milvus.py):
The update() method unconditionally builds {"id": vector_id, "vectors": vector, "metadata": payload} and passes it to client.upsert(). When vector=None, Milvus rejects the record because the vectors field expects FLOAT_VECTOR data.

Qdrant (mem0/vector_stores/qdrant.py):
The update() method constructs PointStruct(id=vector_id, vector=vector, payload=payload). Qdrant's Pydantic model validation rejects vector=None with 6 validation errors.

Both failures are triggered by the same call path — the session ID update logic in Memory.add() and AsyncMemory.add():

self.vector_store.update(
    vector_id=memory_id,
    vector=None,  # Keep same embeddings
    payload=updated_metadata,
)

Solution

Milvus: When vector or payload is None, fetch the existing record via client.get() and use its stored vector/metadata to fill in the missing values before calling upsert(). A single get() call is used even when both are None. Raises ValueError with clear messages if the record doesn't exist or has no vector data.

Qdrant: Use Qdrant's native partial-update APIs instead of a full upsert:

• vector=None → client.set_payload() (metadata-only update)
• payload=None → client.update_vectors() (vector-only update)
• Both provided → client.upsert() (existing behavior, unchanged)

Other vector stores reviewed

No other stores need fixes for this issue.

Testing

New tests added

Milvus (tests/vector_stores/test_milvus.py) — 5 new tests:

• test_update_with_none_vector_fetches_existing — core bug fix: verifies existing vector is fetched and used when vector=None
• test_update_with_none_payload_fetches_existing — verifies existing metadata is preserved when payload=None
• test_update_with_both_none_fetches_existing — verifies only one client.get() call when both are None
• test_update_with_none_vector_raises_on_missing_record — error handling for nonexistent records
• test_update_with_none_vector_raises_on_missing_vector_data — error handling for corrupt records

Qdrant (tests/vector_stores/test_qdrant.py) — 3 new tests:

• test_update_with_none_vector_uses_set_payload — verifies set_payload is called instead of upsert
• test_update_with_none_payload_uses_update_vectors — verifies update_vectors is called instead of upsert
• test_update_with_both_none_is_noop — verifies no client calls when both are None

Backward compatibility verified

• All 14 pre-existing Milvus tests pass (including test_update_uses_upsert which confirms the normal both-provided path is unchanged)
• All 77 pre-existing Qdrant tests pass (including test_update which confirms the normal both-provided path is unchanged)
• Full test suite: 847 passed, 75 skipped, 0 regressions (2 pre-existing Redis failures from missing redis module)

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