From 5c8f7a5397369fc335c3a878434d722c91b99d66 Mon Sep 17 00:00:00 2001
From: Mohamed Shahin <shahin@outlook.ie>
Date: Mon, 24 Aug 2026 10:36:10 +0100
Subject: [PATCH] fix: update quantizer keyerror

---
 test/collection/test_config_update.py  | 70 ++++++++++++++++++++++++++
 weaviate/collections/classes/config.py |  6 +--
 2 files changed, 73 insertions(+), 3 deletions(-)

diff --git a/test/collection/test_config_update.py b/test/collection/test_config_update.py
index 680337291..066d4ecb3 100644
--- a/test/collection/test_config_update.py
+++ b/test/collection/test_config_update.py
@@ -160,3 +160,73 @@ def test_replication_async_config_reset_all_fields() -> None:
     )
     result = update.merge_with_existing(schema)
     assert result["asyncConfig"] == {}
+
+
+def _hfresh_schema(rescore_limit: int = 20) -> dict:
+    """An HFresh schema, which mandates RQ and so carries no pq/bq/sq blocks."""
+    return {
+        "class": "HFreshRQ",
+        "vectorConfig": {
+            "boi": {
+                "vectorizer": {"text2vec-weaviate": {}},
+                "vectorIndexType": "hfresh",
+                "vectorIndexConfig": {
+                    "distance": "cosine",
+                    "maxPostingSizeKB": 1024,
+                    "searchProbe": 8,
+                    "rq": {"enabled": True, "bits": 1, "rescoreLimit": rescore_limit},
+                },
+            }
+        },
+    }
+
+
+def test_updating_rq_on_hfresh_without_pq_block() -> None:
+    """An HFresh schema has no pq block, so the quantizer check must not subscript it."""
+    schema = _hfresh_schema()
+    update = _CollectionConfigUpdate(
+        vector_config=Reconfigure.Vectors.update(
+            name="boi",
+            vector_index_config=Reconfigure.VectorIndex.hfresh(
+                quantizer=Reconfigure.VectorIndex.Quantizer.rq(rescore_limit=500)
+            ),
+        )
+    )
+
+    new_schema = update.merge_with_existing(schema)
+
+    assert new_schema["vectorConfig"]["boi"]["vectorIndexConfig"]["rq"]["rescoreLimit"] == 500
+    assert new_schema["vectorConfig"]["boi"]["vectorIndexConfig"]["rq"]["enabled"]
+
+
+def test_quantizer_check_tolerates_missing_pq_block() -> None:
+    """The rq branch of the quantizer check must tolerate a schema with no pq block."""
+    schema = _hfresh_schema()
+    update = _CollectionConfigUpdate(
+        vector_config=Reconfigure.Vectors.update(
+            name="boi",
+            vector_index_config=Reconfigure.VectorIndex.hfresh(
+                quantizer=Reconfigure.VectorIndex.Quantizer.rq()
+            ),
+        )
+    )
+
+    # No KeyError: rq is the quantizer already in use, so the update is allowed through.
+    update.merge_with_existing(schema)
+
+
+def test_switching_quantizer_still_rejected_when_pq_enabled() -> None:
+    """The guard itself must be unchanged for schemas that do have a pq block."""
+    schema = multi_vector_schema("pq")
+    update = _CollectionConfigUpdate(
+        vectorizer_config=[
+            Reconfigure.NamedVectors.update(
+                name="boi",
+                vector_index_config=Reconfigure.VectorIndex.hnsw(
+                    quantizer=Reconfigure.VectorIndex.Quantizer.rq()
+                ),
+            )
+        ]
+    )
+    with pytest.raises(WeaviateInvalidInputError):
+        update.merge_with_existing(schema)
diff --git a/weaviate/collections/classes/config.py b/weaviate/collections/classes/config.py
index 13298be40..e9effaf15 100644
--- a/weaviate/collections/classes/config.py
+++ b/weaviate/collections/classes/config.py
@@ -1563,7 +1563,7 @@ def __check_quantizers(
             or (
                 isinstance(quantizer, _BQConfigUpdate)
                 and (
-                    vector_index_config["pq"]["enabled"]
+                    vector_index_config.get("pq", {"enabled": False})["enabled"]
                     or vector_index_config.get("sq", {"enabled": False})["enabled"]
                     or vector_index_config.get("rq", {"enabled": False})["enabled"]
                 )
@@ -1571,7 +1571,7 @@ def __check_quantizers(
             or (
                 isinstance(quantizer, _SQConfigUpdate)
                 and (
-                    vector_index_config["pq"]["enabled"]
+                    vector_index_config.get("pq", {"enabled": False})["enabled"]
                     or vector_index_config.get("bq", {"enabled": False})["enabled"]
                     or vector_index_config.get("rq", {"enabled": False})["enabled"]
                 )
@@ -1579,7 +1579,7 @@ def __check_quantizers(
             or (
                 isinstance(quantizer, _RQConfigUpdate)
                 and (
-                    vector_index_config["pq"]["enabled"]
+                    vector_index_config.get("pq", {"enabled": False})["enabled"]
                     or vector_index_config.get("bq", {"enabled": False})["enabled"]
                     or vector_index_config.get("sq", {"enabled": False})["enabled"]
                 )