fix: add BM25 to supported metric type of search iterator (#2301)

issue: milvus-io/milvus#36966

Signed-off-by: Buqian Zheng <[email protected]>

examples/hello_hybrid_bm25.py

@@ -114,7 +114,7 @@ def random_embedding(texts):
 
 # We need to create indices for the vector fields. The indices will be loaded
 # into memory for efficient search.
-sparse_index = {"index_type": "SPARSE_INVERTED_INDEX", "metric_type": "IP"}
+sparse_index = {"index_type": "SPARSE_INVERTED_INDEX", "metric_type": "BM25"}
 col.create_index("sparse_vector", sparse_index)
 dense_index = {"index_type": "FLAT", "metric_type": "IP"}
 col.create_index("dense_vector", dense_index)

pymilvus/orm/constants.py

@@ -25,6 +25,7 @@
 CALC_DIST_METRIC = "metric"
 CALC_DIST_L2 = "L2"
 CALC_DIST_IP = "IP"
+CALC_DIST_BM25 = "BM25"
 CALC_DIST_HAMMING = "HAMMING"
 CALC_DIST_TANIMOTO = "TANIMOTO"
 CALC_DIST_JACCARD = "JACCARD"

pymilvus/orm/iterator.py

@@ -14,6 +14,7 @@
 from .connections import Connections
 from .constants import (
     BATCH_SIZE,
+    CALC_DIST_BM25,
     CALC_DIST_COSINE,
     CALC_DIST_HAMMING,
     CALC_DIST_IP,
@@ -321,7 +322,7 @@ def close(self) -> None:
 def metrics_positive_related(metrics: str) -> bool:
     if metrics in [CALC_DIST_L2, CALC_DIST_JACCARD, CALC_DIST_HAMMING, CALC_DIST_TANIMOTO]:
         return True
-    if metrics in [CALC_DIST_IP, CALC_DIST_COSINE]:
+    if metrics in [CALC_DIST_IP, CALC_DIST_COSINE, CALC_DIST_BM25]:
         return False
     raise MilvusException(message=f"unsupported metrics type for search iteration: {metrics}")