Add AstraDB document loader (#14747)

- **Description:** this adds the AstraDB document loader and an
integration test
  - **Twitter handle:** cbornet_

libs/community/langchain_community/document_loaders/astradb.py

@@ -0,0 +1,101 @@
+import json
+import logging
+import threading
+from queue import Queue
+from typing import Any, Callable, Dict, Iterator, List, Optional
+
+from langchain_core.documents import Document
+
+from langchain_community.document_loaders.base import BaseLoader
+
+logger = logging.getLogger(__name__)
+
+
+class AstraDBLoader(BaseLoader):
+    """Load DataStax Astra DB documents."""
+
+    def __init__(
+        self,
+        collection_name: str,
+        token: Optional[str] = None,
+        api_endpoint: Optional[str] = None,
+        astra_db_client: Optional[Any] = None,  # 'astrapy.db.AstraDB' if passed
+        namespace: Optional[str] = None,
+        filter_criteria: Optional[Dict[str, Any]] = None,
+        projection: Optional[Dict[str, Any]] = None,
+        find_options: Optional[Dict[str, Any]] = None,
+        nb_prefetched: int = 1000,
+        extraction_function: Callable[[Dict], str] = json.dumps,
+    ) -> None:
+        try:
+            from astrapy.db import AstraDB
+        except (ImportError, ModuleNotFoundError):
+            raise ImportError(
+                "Could not import a recent astrapy python package. "
+                "Please install it with `pip install --upgrade astrapy`."
+            )
+
+        # Conflicting-arg checks:
+        if astra_db_client is not None:
+            if token is not None or api_endpoint is not None:
+                raise ValueError(
+                    "You cannot pass 'astra_db_client' to AstraDB if passing "
+                    "'token' and 'api_endpoint'."
+                )
+
+        self.filter = filter_criteria
+        self.projection = projection
+        self.find_options = find_options or {}
+        self.nb_prefetched = nb_prefetched
+        self.extraction_function = extraction_function
+
+        if astra_db_client is not None:
+            astra_db = astra_db_client
+        else:
+            astra_db = AstraDB(
+                token=token,
+                api_endpoint=api_endpoint,
+                namespace=namespace,
+            )
+        self.collection = astra_db.collection(collection_name)
+
+    def load(self) -> List[Document]:
+        """Eagerly load the content."""
+        return list(self.lazy_load())
+
+    def lazy_load(self) -> Iterator[Document]:
+        queue = Queue(self.nb_prefetched)
+        t = threading.Thread(target=self.fetch_results, args=(queue,))
+        t.start()
+        while True:
+            doc = queue.get()
+            if doc is None:
+                break
+            yield doc
+        t.join()
+
+    def fetch_results(self, queue: Queue):
+        self.fetch_page_result(queue)
+        while self.find_options.get("pageState"):
+            self.fetch_page_result(queue)
+        queue.put(None)
+
+    def fetch_page_result(self, queue: Queue):
+        res = self.collection.find(
+            filter=self.filter,
+            options=self.find_options,
+            projection=self.projection,
+            sort=None,
+        )
+        self.find_options["pageState"] = res["data"].get("nextPageState")
+        for doc in res["data"]["documents"]:
+            queue.put(
+                Document(
+                    page_content=self.extraction_function(doc),
+                    metadata={
+                        "namespace": self.collection.astra_db.namespace,
+                        "api_endpoint": self.collection.astra_db.base_url,
+                        "collection": self.collection.collection_name,
+                    },
+                )
+            )