fix: Document field precedence in to_dict()

haystack/dataclasses/document.py

@@ -132,7 +132,7 @@ def to_dict(self, flatten=True) -> Dict[str, Any]:
 
         if flatten:
             meta = data.pop("meta")
-            return {**data, **meta}
+            return {**meta, **data}
 
         return data
 

releasenotes/notes/document-to-dict-field-precedence-578a5e20a185852e.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    Make Document's first-level fields to take precedence over meta fields when flattening the dictionary representation.

test/dataclasses/test_document.py

@@ -185,6 +185,23 @@ def test_to_dict_with_custom_parameters_without_flattening():
     }
 
 
+def test_to_dict_field_precedence():
+    """
+    Test that Document's first-level fields take precedence over meta fields
+    when flattening the dictionary representation.
+    """
+
+    doc = Document(content="from-content", score=0.9, meta={"content": "from-meta", "score": 0.5, "source": "web"})
+
+    flat_dict = doc.to_dict(flatten=True)
+
+    # First-level fields should take precedence
+    assert flat_dict["content"] == "from-content"
+    assert flat_dict["score"] == 0.9
+    # Meta-only fields should be preserved
+    assert flat_dict["source"] == "web"
+
+
 def test_from_dict():
     assert Document.from_dict({}) == Document()