fix readme

packages/leann-backend-hnsw/leann_backend_hnsw/hnsw_backend.py

@@ -14,7 +14,7 @@ from leann.interface import (
 from leann.registry import register_backend
 from leann.searcher_base import BaseSearcher
 
-from .convert_to_csr import convert_hnsw_graph_to_csr
+from .convert_to_csr import convert_hnsw_graph_to_csr, prune_hnsw_embeddings_inplace
 
 logger = logging.getLogger(__name__)
 
@@ -90,8 +90,19 @@ class HNSWBuilder(LeannBackendBuilderInterface):
         index_file = index_dir / f"{index_prefix}.index"
         faiss.write_index(index, str(index_file))
 
+        # Persist ID map so searcher can map FAISS integer labels back to passage IDs
+        try:
+            idmap_file = index_dir / f"{index_prefix}.ids.txt"
+            with open(idmap_file, "w", encoding="utf-8") as f:
+                for id_str in ids:
+                    f.write(str(id_str) + "\n")
+        except Exception as e:
+            logger.warning(f"Failed to write ID map: {e}")
+
         if self.is_compact:
             self._convert_to_csr(index_file)
+        elif self.is_recompute:
+            prune_hnsw_embeddings_inplace(str(index_file))
 
     def _convert_to_csr(self, index_file: Path):
         """Convert built index to CSR format"""
@@ -133,10 +144,10 @@ class HNSWSearcher(BaseSearcher):
         if metric_enum is None:
             raise ValueError(f"Unsupported distance_metric '{self.distance_metric}'.")
 
-        self.is_compact, self.is_pruned = (
-            self.meta.get("is_compact", True),
-            self.meta.get("is_pruned", True),
-        )
+        backend_meta_kwargs = self.meta.get("backend_kwargs", {})
+        self.is_compact = self.meta.get("is_compact", backend_meta_kwargs.get("is_compact", True))
+        default_pruned = backend_meta_kwargs.get("is_recompute", self.is_compact)
+        self.is_pruned = bool(self.meta.get("is_pruned", default_pruned))
 
         index_file = self.index_dir / f"{self.index_path.stem}.index"
         if not index_file.exists():
@@ -150,6 +161,16 @@ class HNSWSearcher(BaseSearcher):
 
         self._index = faiss.read_index(str(index_file), faiss.IO_FLAG_MMAP, hnsw_config)
 
+        # Load ID map if available
+        self._id_map: list[str] = []
+        try:
+            idmap_file = self.index_dir / f"{self.index_path.stem}.ids.txt"
+            if idmap_file.exists():
+                with open(idmap_file, encoding="utf-8") as f:
+                    self._id_map = [line.rstrip("\n") for line in f]
+        except Exception as e:
+            logger.warning(f"Failed to load ID map: {e}")
+
     def search(
         self,
         query: np.ndarray,
@@ -248,6 +269,19 @@ class HNSWSearcher(BaseSearcher):
         )
         search_time = time.time() - search_time
         logger.info(f"  Search time in HNSWSearcher.search() backend: {search_time} seconds")
-        string_labels = [[str(int_label) for int_label in batch_labels] for batch_labels in labels]
+        if self._id_map:
+
+            def map_label(x: int) -> str:
+                if 0 <= x < len(self._id_map):
+                    return self._id_map[x]
+                return str(x)
+
+            string_labels = [
+                [map_label(int(label)) for label in batch_labels] for batch_labels in labels
+            ]
+        else:
+            string_labels = [
+                [str(int_label) for int_label in batch_labels] for batch_labels in labels
+            ]
 
         return {"labels": string_labels, "distances": distances}