Fix ColbertVectorStore as_retriever() (#611)

Author: cbornet

libs/langchain/ragstack_langchain/colbert/colbert_vector_store.py

@@ -1,8 +1,7 @@
 from typing import Any, Iterable, List, Optional, Tuple, Type, TypeVar
 
 from langchain_core.documents import Document
-from langchain_core.retrievers import BaseRetriever
-from langchain_core.vectorstores import VectorStore
+from langchain_core.vectorstores import VectorStore, VectorStoreRetriever
 from ragstack_colbert import Chunk
 from ragstack_colbert import ColbertVectorStore as RagstackColbertVectorStore
 from ragstack_colbert.base_database import BaseDatabase as ColbertBaseDatabase
@@ -13,8 +12,6 @@
 from ragstack_colbert.base_vector_store import BaseVectorStore as ColbertBaseVectorStore
 from typing_extensions import override
 
-from .colbert_retriever import ColbertRetriever
-
 CVS = TypeVar("CVS", bound="ColbertVectorStore")
 
 
@@ -282,8 +279,11 @@ async def afrom_texts(
         return instance
 
     @override
-    def as_retriever(self, k: Optional[int] = 5, **kwargs: Any) -> BaseRetriever:
+    def as_retriever(self, k: Optional[int] = 5, **kwargs: Any) -> VectorStoreRetriever:
         """Return a VectorStoreRetriever initialized from this VectorStore."""
-        return ColbertRetriever(
-            retriever=self._vector_store.as_retriever(), k=k, **kwargs
-        )
+        search_kwargs = kwargs.pop("search_kwargs", {})
+        search_kwargs["k"] = k
+        search_type = kwargs.get("search_type", "similarity")
+        if search_type != "similarity":
+            raise ValueError(f"Unsupported search type: {search_type}")
+        return super().as_retriever(search_kwargs=search_kwargs, **kwargs)