fix: update meta data before initializing new Document in DocumentSplitter (#8745)

* updated DocumentSplitter

issue #8741

* release note

* updated DocumentSplitter

in _create_docs_from_splits function initialize a new variable copied_mete instead to overwrite meta

* added test

test_duplicate_pages_get_different_doc_id

* fix fmt

---------

Co-authored-by: Stefano Fiorucci <stefanofiorucci@gmail.com>

haystack/components/preprocessors/document_splitter.py

@@ -323,11 +323,11 @@ class DocumentSplitter:
         documents: List[Document] = []
 
         for i, (txt, split_idx) in enumerate(zip(text_splits, splits_start_idxs)):
-            meta = deepcopy(meta)
-            doc = Document(content=txt, meta=meta)
-            doc.meta["page_number"] = splits_pages[i]
-            doc.meta["split_id"] = i
-            doc.meta["split_idx_start"] = split_idx
+            copied_meta = deepcopy(meta)
+            copied_meta["page_number"] = splits_pages[i]
+            copied_meta["split_id"] = i
+            copied_meta["split_idx_start"] = split_idx
+            doc = Document(content=txt, meta=copied_meta)
             documents.append(doc)
 
             if self.split_overlap <= 0:

releasenotes/notes/updated-documentsplitter-762c4409cbc296e6.yaml

@@ -0,0 +1,4 @@
+---
+enhancements:
+  - |
+    Updated Document's meta data after initializing the Document in DocumentSplitter as requested in issue #8741

test/components/preprocessors/test_document_splitter.py

@@ -827,3 +827,11 @@ class TestSplittingNLTKSentenceSplitter:
         assert deserialized.respect_sentence_boundary == True
         assert hasattr(deserialized, "sentence_splitter")
         assert deserialized.language == "de"
+
+    def test_duplicate_pages_get_different_doc_id(self):
+        splitter = DocumentSplitter(split_by="page", split_length=1)
+        doc1 = Document(content="This is some text.\fThis is some text.\fThis is some text.\fThis is some text.")
+        splitter.warm_up()
+        result = splitter.run(documents=[doc1])
+
+        assert len({doc.id for doc in result["documents"]}) == 4