Repository: deepset-ai/haystack

Issue:
Make `window_size` a runtime option for `SentenceWindowRetriever`
**Is your feature request related to a problem? Please describe.**
Currently, `window_size` is only provided at initialization. There is no need for this. Ideally, we can allow users to decide the size of the window at runtime, allowing them to change it when we call `pipeline.run()`.

**Describe the solution you'd like**
Make `window_size` an argument for the `run` method of this component

**Addition**
This will make the new sentence window retreval tutorial simpler

Discussion:

Solution patch:
diff --git a/haystack/components/retrievers/sentence_window_retriever.py b/haystack/components/retrievers/sentence_window_retriever.py
index abc68850c1..fbc389ed3e 100644
--- a/haystack/components/retrievers/sentence_window_retriever.py
+++ b/haystack/components/retrievers/sentence_window_retriever.py
@@ -2,7 +2,7 @@
 #
 # SPDX-License-Identifier: Apache-2.0
 
-from typing import Any, Dict, List
+from typing import Any, Dict, List, Optional
 
 from haystack import Document, component, default_from_dict, default_to_dict
 from haystack.document_stores.types import DocumentStore
@@ -84,7 +84,7 @@ def __init__(self, document_store: DocumentStore, window_size: int = 3):
 
         :param document_store: The Document Store to retrieve the surrounding documents from.
         :param window_size: The number of documents to retrieve before and after the relevant one.
-        For example, `window_size: 2` fetches 2 preceding and 2 following documents.
+                For example, `window_size: 2` fetches 2 preceding and 2 following documents.
         """
         if window_size < 1:
             raise ValueError("The window_size parameter must be greater than 0.")
@@ -144,7 +144,7 @@ def from_dict(cls, data: Dict[str, Any]) -> "SentenceWindowRetriever":
         return default_from_dict(cls, data)
 
     @component.output_types(context_windows=List[str], context_documents=List[List[Document]])
-    def run(self, retrieved_documents: List[Document]):
+    def run(self, retrieved_documents: List[Document], window_size: Optional[int] = None):
         """
         Based on the `source_id` and on the `doc.meta['split_id']` get surrounding documents from the document store.
 
@@ -152,6 +152,8 @@ def run(self, retrieved_documents: List[Document]):
         document from the document store.
 
         :param retrieved_documents: List of retrieved documents from the previous retriever.
+        :param window_size: The number of documents to retrieve before and after the relevant one. This will overwrite
+                            the `window_size` parameter set in the constructor.
         :returns:
             A dictionary with the following keys:
                 - `context_windows`: A list of strings, where each string represents the concatenated text from the
@@ -161,6 +163,10 @@ def run(self, retrieved_documents: List[Document]):
                                      `retrieved_documents`.
 
         """
+        window_size = window_size or self.window_size
+
+        if window_size < 1:
+            raise ValueError("The window_size parameter must be greater than 0.")
 
         if not all("split_id" in doc.meta for doc in retrieved_documents):
             raise ValueError("The retrieved documents must have 'split_id' in the metadata.")
@@ -173,8 +179,8 @@ def run(self, retrieved_documents: List[Document]):
         for doc in retrieved_documents:
             source_id = doc.meta["source_id"]
             split_id = doc.meta["split_id"]
-            min_before = min(list(range(split_id - 1, split_id - self.window_size - 1, -1)))
-            max_after = max(list(range(split_id + 1, split_id + self.window_size + 1, 1)))
+            min_before = min(list(range(split_id - 1, split_id - window_size - 1, -1)))
+            max_after = max(list(range(split_id + 1, split_id + window_size + 1, 1)))
             context_docs = self.document_store.filter_documents(
                 {
                     "operator": "AND",
diff --git a/releasenotes/notes/add-window-size-parameter-runtime-e841c4471f9d6b9c.yaml b/releasenotes/notes/add-window-size-parameter-runtime-e841c4471f9d6b9c.yaml
new file mode 100644
index 0000000000..e9d5aa2ed7
--- /dev/null
+++ b/releasenotes/notes/add-window-size-parameter-runtime-e841c4471f9d6b9c.yaml
@@ -0,0 +1,4 @@
+---
+enhancements:
+  - |
+    The SentenceWindowRetriever now supports the `window_size` parameter at run time, overwriting the value set in the constructor.


Test patch:
diff --git a/test/components/retrievers/test_sentence_window_retriever.py b/test/components/retrievers/test_sentence_window_retriever.py
index d05f478023..786d278dd6 100644
--- a/test/components/retrievers/test_sentence_window_retriever.py
+++ b/test/components/retrievers/test_sentence_window_retriever.py
@@ -1,10 +1,10 @@
 import pytest
 
-from haystack import Document, DeserializationError, Pipeline
+from haystack import DeserializationError, Document, Pipeline
+from haystack.components.preprocessors import DocumentSplitter
 from haystack.components.retrievers import InMemoryBM25Retriever
 from haystack.components.retrievers.sentence_window_retriever import SentenceWindowRetriever
 from haystack.document_stores.in_memory import InMemoryDocumentStore
-from haystack.components.preprocessors import DocumentSplitter
 
 
 class TestSentenceWindowRetriever:
@@ -118,9 +118,32 @@ def test_document_without_source_id(self):
             retriever = SentenceWindowRetriever(document_store=InMemoryDocumentStore(), window_size=3)
             retriever.run(retrieved_documents=docs)
 
+    def test_run_invalid_window_size(self):
+        docs = [Document(content="This is a text with some words. There is a ", meta={"id": "doc_0", "split_id": 0})]
+        with pytest.raises(ValueError):
+            retriever = SentenceWindowRetriever(document_store=InMemoryDocumentStore(), window_size=0)
+            retriever.run(retrieved_documents=docs)
+
+    def test_constructor_parameter_does_not_change(self):
+        retriever = SentenceWindowRetriever(InMemoryDocumentStore(), window_size=5)
+        assert retriever.window_size == 5
+
+        doc = {
+            "id": "doc_0",
+            "content": "This is a text with some words. There is a ",
+            "source_id": "c5d7c632affc486d0cfe7b3c0f4dc1d3896ea720da2b538d6d10b104a3df5f99",
+            "page_number": 1,
+            "split_id": 0,
+            "split_idx_start": 0,
+            "_split_overlap": [{"doc_id": "doc_1", "range": (0, 23)}],
+        }
+
+        retriever.run(retrieved_documents=[Document.from_dict(doc)], window_size=1)
+        assert retriever.window_size == 5
+
     @pytest.mark.integration
     def test_run_with_pipeline(self):
-        splitter = DocumentSplitter(split_length=10, split_overlap=5, split_by="word")
+        splitter = DocumentSplitter(split_length=1, split_overlap=0, split_by="sentence")
         text = (
             "This is a text with some words. There is a second sentence. And there is also a third sentence. "
             "It also contains a fourth sentence. And a fifth sentence. And a sixth sentence. And a seventh sentence"
@@ -139,11 +162,17 @@ def test_run_with_pipeline(self):
         result = pipe.run({"bm25_retriever": {"query": "third"}})
 
         assert result["sentence_window_retriever"]["context_windows"] == [
-            "some words. There is a second sentence. And there is also a third sentence. It also "
-            "contains a fourth sentence. And a fifth sentence. And a sixth sentence. And a "
+            "This is a text with some words. There is a second sentence. And there is also a third sentence. "
+            "It also contains a fourth sentence. And a fifth sentence."
         ]
         assert len(result["sentence_window_retriever"]["context_documents"][0]) == 5
 
+        result = pipe.run({"bm25_retriever": {"query": "third"}, "sentence_window_retriever": {"window_size": 1}})
+        assert result["sentence_window_retriever"]["context_windows"] == [
+            " There is a second sentence. And there is also a third sentence. It also contains a fourth sentence."
+        ]
+        assert len(result["sentence_window_retriever"]["context_documents"][0]) == 3
+
     @pytest.mark.integration
     def test_serialization_deserialization_in_pipeline(self):
         doc_store = InMemoryDocumentStore()