feat: add ttl and time_field support to CacheChecker

docs-website/docs/pipeline-components/caching/cachechecker.mdx

@@ -15,8 +15,9 @@ This component checks for the presence of documents in a Document Store based on
 | --- | --- |
 | **Most common position in a pipeline** | Flexible |
 | **Mandatory init variables** | `document_store`: A Document Store instance  <br /> <br />`cache_field`: Name of the document's metadata field |
+| **Optional init variables** | `ttl`: Time-to-live for cache entries. Can be a `timedelta` or a number of seconds. Defaults to `None`, meaning cache entries never expire  <br /> <br />`time_field`: Name of the document's metadata field holding the cache timestamp, used only when `ttl` is set. Defaults to `"cached_at"` |
 | **Mandatory run variables** | `items`: A list of values associated with the `cache_field` in documents |
-| **Output variables** | `hits`: A list of documents that were found with the specified value in cache  <br /> <br />`misses`: A list of values that could not be found |
+| **Output variables** | `hits`: A list of documents that were found with the specified value in cache and, if a `ttl` is configured, are still within it  <br /> <br />`misses`: A list of values that could not be found, or whose only matches had expired |
 | **API reference** | [Caching](/reference/caching-api) |
 | **GitHub link** | https://github.com/deepset-ai/haystack/blob/main/haystack/components/caching/cache_checker.py |
 | **Package name** | `haystack-ai` |
@@ -63,6 +64,54 @@ print(
 )  # Values that were not found in the cache, like: ["ABCDE"]
 ```
 
+### Expiring cache entries with a TTL
+
+`CacheChecker` treats a cache entry as valid forever unless you tell it otherwise. For data that goes stale — like a periodically re-crawled URL or a document whose source changes over time — pass a `ttl` so old entries stop counting as hits.
+
+`CacheChecker` doesn't stamp documents itself; it only reads a timestamp that was already written. Set that timestamp yourself wherever you write documents into the store:
+
+```python
+from datetime import datetime, timezone
+from haystack import Document
+
+document = Document(
+    content="doc1",
+    meta={
+        "url": "https://example.com/resource",
+        "cached_at": datetime.now(timezone.utc),
+    },
+)
+my_doc_store.write_documents([document])
+```
+
+Then configure `CacheChecker` with a `ttl` so it knows how far back to look:
+
+```python
+from datetime import timedelta
+from haystack.components.caching import CacheChecker
+
+cache_checker = CacheChecker(
+    document_store=my_doc_store,
+    cache_field="url",
+    ttl=timedelta(hours=24),
+)
+```
+
+With this configuration, `checker.run(items=["https://example.com/resource"])` only reports a hit if `cached_at` is less than 24 hours old. Anything older — or a document that never got a `cached_at` value in the first place — comes back in `misses`, exactly as if it had never been cached at all.
+
+The timestamp field name is configurable via `time_field` (it defaults to `"cached_at"`), which is useful if your metadata already tracks time under a different key, such as `created_at` or `last_indexed`:
+
+```python
+cache_checker = CacheChecker(
+    document_store=my_doc_store,
+    cache_field="url",
+    ttl=timedelta(hours=24),
+    time_field="last_indexed",
+)
+```
+
+Leaving `ttl` unset keeps the component's original behavior: cache entries never expire, and `time_field` is ignored entirely.
+
 ### In a pipeline
 
 ```python

haystack/components/caching/cache_checker.py

@@ -2,6 +2,7 @@
 #
 # SPDX-License-Identifier: Apache-2.0
 
+from datetime import datetime, timedelta, timezone
 from typing import Any
 
 from haystack import Document, component, default_from_dict, default_to_dict
@@ -37,7 +38,14 @@ class CacheChecker:
     ```
     """
 
-    def __init__(self, document_store: DocumentStore, cache_field: str) -> None:
+    def __init__(
+        self,
+        document_store: DocumentStore,
+        cache_field: str,
+        *,
+        ttl: float | timedelta | None = None,
+        time_field: str = "cached_at",
+    ) -> None:
         """
         Creates a CacheChecker component.
 
@@ -49,6 +57,8 @@ def __init__(self, document_store: DocumentStore, cache_field: str) -> None:
         """
         self.document_store = document_store
         self.cache_field = cache_field
+        self.ttl = timedelta(seconds=ttl) if isinstance(ttl, (int, float)) else ttl
+        self.time_field = time_field
 
     def to_dict(self) -> dict[str, Any]:
         """
@@ -57,7 +67,46 @@ def to_dict(self) -> dict[str, Any]:
         :returns:
             Dictionary with serialized data.
         """
-        return default_to_dict(self, document_store=self.document_store, cache_field=self.cache_field)
+        return default_to_dict(
+            self,
+            document_store=self.document_store,
+            cache_field=self.cache_field,
+            ttl=self.ttl.total_seconds() if self.ttl is not None else None,
+            time_field=self.time_field,
+        )
+
+    def _is_fresh(self, document: Document) -> bool:
+        """
+        Checks whether a cached document is still within its TTL.
+
+        Always returns True when no `ttl` is configured, to preserve the original non-expiring behavior.
+
+        :param document:
+            The candidate cache-hit document.
+        :returns:
+            True if the document should count as a cache hit, False if it should be treated as expired.
+        """
+        if self.ttl is None:
+            return True
+
+        cached_at = document.meta.get(self.time_field)
+        if cached_at is None:
+            # ttl is enabled but the document was never stamped with a cache time: treat as stale
+            return False
+
+        if isinstance(cached_at, str):
+            try:
+                cached_at = datetime.fromisoformat(cached_at)
+            except ValueError:
+                return False
+
+        if not isinstance(cached_at, datetime):
+            return False
+
+        if cached_at.tzinfo is None:
+            cached_at = cached_at.replace(tzinfo=timezone.utc)
+
+        return datetime.now(timezone.utc) - cached_at < self.ttl
 
     @classmethod
     def from_dict(cls, data: dict[str, Any]) -> "CacheChecker":
@@ -89,10 +138,12 @@ def run(self, items: list[Any]) -> dict[str, Any]:
         for item in items:
             filters = {"field": self.cache_field, "operator": "==", "value": item}
             found = self.document_store.filter_documents(filters=filters)
-            if found:
-                found_documents.extend(found)
+            fresh = [doc for doc in found if self._is_fresh(doc)]
+            if fresh:
+                found_documents.extend(fresh)
             else:
                 misses.append(item)
+
         return {"hits": found_documents, "misses": misses}
 
     @component.output_types(hits=list[Document], misses=list)
@@ -116,8 +167,9 @@ async def run_async(self, items: list[Any]) -> dict[str, Any]:
         for item in items:
             filters = {"field": self.cache_field, "operator": "==", "value": item}
             found = await self.document_store.filter_documents_async(filters=filters)
-            if found:
-                found_documents.extend(found)
+            fresh = [doc for doc in found if self._is_fresh(doc)]
+            if fresh:
+                found_documents.extend(fresh)
             else:
                 misses.append(item)
         return {"hits": found_documents, "misses": misses}

releasenotes/notes/cache-checker-ttl-6842b76bcab8efd4.yaml

@@ -0,0 +1,5 @@
+---
+enhancements:
+    Add optional TTL support to ``CacheChecker`` to allow cached documents
+    to expire after a configurable amount of time. The cache timestamp
+    field can be customized using the ``time_field`` parameter.

test/components/caching/test_cache_checker.py

@@ -2,6 +2,7 @@
 #
 # SPDX-License-Identifier: Apache-2.0
 
+from datetime import datetime, timedelta, timezone
 from unittest.mock import Mock, patch
 
 import pytest
@@ -22,21 +23,36 @@ def test_to_dict(self):
             "init_parameters": {
                 "document_store": {"type": "haystack.testing.factory.MockedDocumentStore", "init_parameters": {}},
                 "cache_field": "url",
+                "ttl": None,
+                "time_field": "cached_at",
             },
         }
 
     def test_to_dict_with_custom_init_parameters(self):
         mocked_docstore_class = document_store_class("MockedDocumentStore")
-        component = CacheChecker(document_store=mocked_docstore_class(), cache_field="my_url_field")
+        component = CacheChecker(
+            document_store=mocked_docstore_class(),
+            cache_field="my_url_field",
+            ttl=timedelta(hours=1),
+            time_field="my_time_field",
+        )
         data = component.to_dict()
         assert data == {
             "type": "haystack.components.caching.cache_checker.CacheChecker",
             "init_parameters": {
                 "document_store": {"type": "haystack.testing.factory.MockedDocumentStore", "init_parameters": {}},
                 "cache_field": "my_url_field",
+                "ttl": 3600.0,
+                "time_field": "my_time_field",
             },
         }
 
+    def test_to_dict_with_numeric_ttl(self):
+        mocked_docstore_class = document_store_class("MockedDocumentStore")
+        component = CacheChecker(document_store=mocked_docstore_class(), cache_field="url", ttl=90)
+        data = component.to_dict()
+        assert data["init_parameters"]["ttl"] == 90.0
+
     def test_from_dict(self):
         data = {
             "type": "haystack.components.caching.cache_checker.CacheChecker",
@@ -46,11 +62,15 @@ def test_from_dict(self):
                     "init_parameters": {},
                 },
                 "cache_field": "my_url_field",
+                "ttl": 3600.0,
+                "time_field": "my_time_field",
             },
         }
         component = CacheChecker.from_dict(data)
         assert isinstance(component.document_store, InMemoryDocumentStore)
         assert component.cache_field == "my_url_field"
+        assert component.ttl == timedelta(hours=1)
+        assert component.time_field == "my_time_field"
 
     def test_from_dict_without_docstore(self):
         data = {"type": "haystack.components.caching.cache_checker.CacheChecker", "init_parameters": {}}
@@ -103,3 +123,84 @@ def test_close(self):
         checker = CacheChecker(document_store=nonclosable_document_store, cache_field="url")
         checker.close()
         assert nonclosable_document_store.mock_calls == []
+
+    def test_run_with_ttl_fresh_hit(self, in_memory_doc_store):
+        fresh_doc = Document(
+            content="doc1",
+            meta={"url": "https://example.com/1", "cached_at": datetime.now(timezone.utc) - timedelta(minutes=5)},
+        )
+        in_memory_doc_store.write_documents([fresh_doc])
+        checker = CacheChecker(in_memory_doc_store, cache_field="url", ttl=timedelta(hours=1))
+        results = checker.run(items=["https://example.com/1"])
+        assert results == {"hits": [fresh_doc], "misses": []}
+
+    def test_run_with_ttl_expired_is_miss(self, in_memory_doc_store):
+        stale_doc = Document(
+            content="doc1",
+            meta={"url": "https://example.com/1", "cached_at": datetime.now(timezone.utc) - timedelta(hours=2)},
+        )
+        in_memory_doc_store.write_documents([stale_doc])
+        checker = CacheChecker(in_memory_doc_store, cache_field="url", ttl=timedelta(hours=1))
+        results = checker.run(items=["https://example.com/1"])
+        assert results == {"hits": [], "misses": ["https://example.com/1"]}
+
+    def test_run_with_ttl_missing_time_field_is_miss(self, in_memory_doc_store):
+        undated_doc = Document(content="doc1", meta={"url": "https://example.com/1"})
+        in_memory_doc_store.write_documents([undated_doc])
+        checker = CacheChecker(in_memory_doc_store, cache_field="url", ttl=timedelta(hours=1))
+        results = checker.run(items=["https://example.com/1"])
+        assert results == {"hits": [], "misses": ["https://example.com/1"]}
+
+    def test_run_with_ttl_iso_string_timestamp(self, in_memory_doc_store):
+        fresh_doc = Document(
+            content="doc1",
+            meta={
+                "url": "https://example.com/1",
+                "cached_at": (datetime.now(timezone.utc) - timedelta(minutes=5)).isoformat(),
+            },
+        )
+        in_memory_doc_store.write_documents([fresh_doc])
+        checker = CacheChecker(in_memory_doc_store, cache_field="url", ttl=timedelta(hours=1))
+        results = checker.run(items=["https://example.com/1"])
+        assert results == {"hits": [fresh_doc], "misses": []}
+
+    def test_run_without_ttl_ignores_time_field(self, in_memory_doc_store):
+        # backward compatibility: no ttl configured means entries never expire, regardless of cached_at
+        old_doc = Document(
+            content="doc1",
+            meta={"url": "https://example.com/1", "cached_at": datetime.now(timezone.utc) - timedelta(days=365)},
+        )
+        in_memory_doc_store.write_documents([old_doc])
+        checker = CacheChecker(in_memory_doc_store, cache_field="url")
+        results = checker.run(items=["https://example.com/1"])
+        assert results == {"hits": [old_doc], "misses": []}
+
+    def test_run_with_ttl_naive_datetime_timestamp(self, in_memory_doc_store):
+        # meta timestamp with no tzinfo at all (not datetime.now(timezone.utc))
+        fresh_doc = Document(
+            content="doc1",
+            meta={"url": "https://example.com/1", "cached_at": datetime.now() - timedelta(minutes=5)},  # noqa: DTZ005
+        )
+        in_memory_doc_store.write_documents([fresh_doc])
+        checker = CacheChecker(in_memory_doc_store, cache_field="url", ttl=timedelta(hours=1))
+        results = checker.run(items=["https://example.com/1"])
+        assert results == {"hits": [fresh_doc], "misses": []}
+
+    def test_run_with_ttl_malformed_iso_string_is_miss(self, in_memory_doc_store):
+        bad_doc = Document(content="doc1", meta={"url": "https://example.com/1", "cached_at": "not-a-timestamp"})
+        in_memory_doc_store.write_documents([bad_doc])
+        checker = CacheChecker(in_memory_doc_store, cache_field="url", ttl=timedelta(hours=1))
+        results = checker.run(items=["https://example.com/1"])
+        assert results == {"hits": [], "misses": ["https://example.com/1"]}
+
+    def test_run_with_ttl_non_datetime_timestamp_is_miss(self, in_memory_doc_store):
+        bad_doc = Document(content="doc1", meta={"url": "https://example.com/1", "cached_at": 12345})
+        in_memory_doc_store.write_documents([bad_doc])
+        checker = CacheChecker(in_memory_doc_store, cache_field="url", ttl=timedelta(hours=1))
+        results = checker.run(items=["https://example.com/1"])
+        assert results == {"hits": [], "misses": ["https://example.com/1"]}
+
+    def test_ttl_accepts_numeric_seconds(self):
+        mocked_docstore_class = document_store_class("MockedDocumentStore")
+        checker = CacheChecker(document_store=mocked_docstore_class(), cache_field="url", ttl=3600)
+        assert checker.ttl == timedelta(hours=1)

test/components/caching/test_cache_checker_async.py

@@ -2,6 +2,7 @@
 #
 # SPDX-License-Identifier: Apache-2.0
 
+from datetime import datetime, timedelta, timezone
 from unittest.mock import AsyncMock, MagicMock, Mock
 
 import pytest
@@ -73,3 +74,25 @@ async def test_close_async(self):
         checker = CacheChecker(document_store=nonclosable_document_store, cache_field="url")
         await checker.close_async()
         assert nonclosable_document_store.mock_calls == []
+
+    @pytest.mark.asyncio
+    async def test_run_async_with_ttl_fresh_hit(self, in_memory_doc_store):
+        fresh_doc = Document(
+            content="doc1",
+            meta={"url": "https://example.com/1", "cached_at": datetime.now(timezone.utc) - timedelta(minutes=5)},
+        )
+        in_memory_doc_store.write_documents([fresh_doc])
+        checker = CacheChecker(in_memory_doc_store, cache_field="url", ttl=timedelta(hours=1))
+        results = await checker.run_async(items=["https://example.com/1"])
+        assert results == {"hits": [fresh_doc], "misses": []}
+
+    @pytest.mark.asyncio
+    async def test_run_async_with_ttl_expired_is_miss(self, in_memory_doc_store):
+        stale_doc = Document(
+            content="doc1",
+            meta={"url": "https://example.com/1", "cached_at": datetime.now(timezone.utc) - timedelta(hours=2)},
+        )
+        in_memory_doc_store.write_documents([stale_doc])
+        checker = CacheChecker(in_memory_doc_store, cache_field="url", ttl=timedelta(hours=1))
+        results = await checker.run_async(items=["https://example.com/1"])
+        assert results == {"hits": [], "misses": ["https://example.com/1"]}