[Fix] Fix Cassandra Document loader default page content mapper (#16273)

We can't use `json.dumps` by default as many types returned by the
cassandra driver are not serializable. It's safer to use `str` and let
users define their own custom `page_content_mapper` if needed.

libs/community/langchain_community/document_loaders/__init__.py

@@ -59,6 +59,7 @@ from langchain_community.document_loaders.blob_loaders import (
 from langchain_community.document_loaders.blockchain import BlockchainDocumentLoader
 from langchain_community.document_loaders.brave_search import BraveSearchLoader
 from langchain_community.document_loaders.browserless import BrowserlessLoader
+from langchain_community.document_loaders.cassandra import CassandraLoader
 from langchain_community.document_loaders.chatgpt import ChatGPTLoader
 from langchain_community.document_loaders.chromium import AsyncChromiumLoader
 from langchain_community.document_loaders.college_confidential import (
@@ -267,6 +268,7 @@ __all__ = [
     "BlockchainDocumentLoader",
     "BraveSearchLoader",
     "BrowserlessLoader",
+    "CassandraLoader",
     "CSVLoader",
     "ChatGPTLoader",
     "CoNLLULoader",

libs/community/langchain_community/document_loaders/cassandra.py

@@ -1,4 +1,3 @@
-import json
 from typing import (
     TYPE_CHECKING,
     Any,
@@ -14,13 +13,6 @@ from langchain_core.documents import Document
 
 from langchain_community.document_loaders.base import BaseLoader
 
-
-def default_page_content_mapper(row: Any) -> str:
-    if hasattr(row, "_asdict"):
-        return json.dumps(row._asdict())
-    return json.dumps(row)
-
-
 _NOT_SET = object()
 
 if TYPE_CHECKING:
@@ -36,7 +28,7 @@ class CassandraLoader(BaseLoader):
         session: Optional["Session"] = None,
         keyspace: Optional[str] = None,
         query: Optional[Union[str, "Statement"]] = None,
-        page_content_mapper: Callable[[Any], str] = default_page_content_mapper,
+        page_content_mapper: Callable[[Any], str] = str,
         metadata_mapper: Callable[[Any], dict] = lambda _: {},
         *,
         query_parameters: Union[dict, Sequence] = None,
@@ -61,6 +53,7 @@ class CassandraLoader(BaseLoader):
             query: The query used to load the data.
                 (do not use together with the table parameter)
             page_content_mapper: a function to convert a row to string page content.
+                Defaults to the str representation of the row.
             query_parameters: The query parameters used when calling session.execute .
             query_timeout: The query timeout used when calling session.execute .
             query_custom_payload: The query custom_payload used when calling

libs/community/tests/integration_tests/document_loaders/test_cassandra.py

@@ -59,11 +59,11 @@ def test_loader_table(keyspace: str) -> None:
     loader = CassandraLoader(table=CASSANDRA_TABLE)
     assert loader.load() == [
         Document(
-            page_content='{"row_id": "id1", "body_blob": "text1"}',
+            page_content="Row(row_id='id1', body_blob='text1')",
             metadata={"table": CASSANDRA_TABLE, "keyspace": keyspace},
         ),
         Document(
-            page_content='{"row_id": "id2", "body_blob": "text2"}',
+            page_content="Row(row_id='id2', body_blob='text2')",
             metadata={"table": CASSANDRA_TABLE, "keyspace": keyspace},
         ),
     ]
@@ -74,8 +74,8 @@ def test_loader_query(keyspace: str) -> None:
         query=f"SELECT body_blob FROM {keyspace}.{CASSANDRA_TABLE}"
     )
     assert loader.load() == [
-        Document(page_content='{"body_blob": "text1"}'),
-        Document(page_content='{"body_blob": "text2"}'),
+        Document(page_content="Row(body_blob='text1')"),
+        Document(page_content="Row(body_blob='text2')"),
     ]
 
 
@@ -103,7 +103,7 @@ def test_loader_metadata_mapper(keyspace: str) -> None:
     loader = CassandraLoader(table=CASSANDRA_TABLE, metadata_mapper=mapper)
     assert loader.load() == [
         Document(
-            page_content='{"row_id": "id1", "body_blob": "text1"}',
+            page_content="Row(row_id='id1', body_blob='text1')",
             metadata={
                 "table": CASSANDRA_TABLE,
                 "keyspace": keyspace,
@@ -111,7 +111,7 @@ def test_loader_metadata_mapper(keyspace: str) -> None:
             },
         ),
         Document(
-            page_content='{"row_id": "id2", "body_blob": "text2"}',
+            page_content="Row(row_id='id2', body_blob='text2')",
             metadata={
                 "table": CASSANDRA_TABLE,
                 "keyspace": keyspace,

libs/community/tests/unit_tests/document_loaders/test_imports.py

@@ -37,6 +37,7 @@ EXPECTED_ALL = [
     "BlockchainDocumentLoader",
     "BraveSearchLoader",
     "BrowserlessLoader",
+    "CassandraLoader",
     "CSVLoader",
     "ChatGPTLoader",
     "CoNLLULoader",