feat: Add serialization/deserialization to DoclingConverter (#3267)

Author: sjrl

integrations/docling/src/haystack_integrations/components/converters/docling/converter.py

@@ -10,14 +10,18 @@
 from typing import Any
 
 from docling_core.types.io import DocumentStream
-from haystack import Document, component
+from haystack import Document, component, logging
 from haystack.components.converters.utils import normalize_metadata
+from haystack.core.serialization import default_from_dict, default_to_dict
 from haystack.dataclasses import ByteStream
+from haystack.utils.base_serialization import deserialize_class_instance, serialize_class_instance
 
 from docling.chunking import BaseChunk, BaseChunker, HybridChunker
 from docling.datamodel.document import DoclingDocument
 from docling.document_converter import DocumentConverter
 
+logger = logging.getLogger(__name__)
+
 
 def _bytestream_to_document_stream(source: ByteStream) -> DocumentStream:
     """
@@ -63,6 +67,15 @@ def extract_dl_doc_meta(self, dl_doc: DoclingDocument) -> dict[str, Any]:
         """Extract Docling document meta."""
         raise NotImplementedError()
 
+    def to_dict(self) -> dict[str, Any]:
+        """Serialize to a dictionary."""
+        return {}
+
+    @classmethod
+    def from_dict(cls, data: dict[str, Any]) -> "BaseMetaExtractor":  # noqa: ARG003
+        """Deserialize from a dictionary."""
+        return cls()
+
 
 class MetaExtractor(BaseMetaExtractor):
     """MetaExtractor."""
@@ -123,6 +136,53 @@ def __init__(
             self._chunker_instance = chunker or HybridChunker()
         self._meta_extractor_instance = meta_extractor or MetaExtractor()
 
+    def to_dict(self) -> dict[str, Any]:
+        """Serialize this component to a dictionary."""
+        if self.converter is not None:
+            logger.warning(
+                "DoclingConverter.to_dict: the 'converter' parameter cannot be serialized and will be dropped. "
+                "The component will use the default DocumentConverter when restored from the serialized form."
+            )
+        if self.chunker is not None:
+            logger.warning(
+                "DoclingConverter.to_dict: the 'chunker' parameter cannot be serialized and will be dropped. "
+                "The component will use the default chunker when restored from the serialized form."
+            )
+
+        meta_extractor_data = None
+        if self.meta_extractor is not None:
+            meta_extractor_data = serialize_class_instance(self.meta_extractor)
+
+        return default_to_dict(
+            self,
+            converter=None,
+            convert_kwargs=self.convert_kwargs,
+            export_type=self.export_type.value,
+            md_export_kwargs=self.md_export_kwargs,
+            chunker=None,
+            meta_extractor=meta_extractor_data,
+        )
+
+    @classmethod
+    def from_dict(cls, data: dict[str, Any]) -> "DoclingConverter":
+        """
+        Deserialize this component from a dictionary.
+
+        The `converter` and `chunker` parameters are not serializable and are always ignored during
+        deserialization; the restored instance will use the default `DocumentConverter` and `HybridChunker`
+        respectively.
+
+        :param data: Dictionary with keys `type` and `init_parameters`, as produced by `to_dict`.
+        :returns: A new `DoclingConverter` instance.
+        """
+        init_params = data.get("init_parameters", {})
+
+        meta_extractor_data = init_params.get("meta_extractor")
+        if meta_extractor_data is not None:
+            init_params["meta_extractor"] = deserialize_class_instance(meta_extractor_data)
+
+        return default_from_dict(cls, data)
+
     @component.output_types(documents=list[Document])
     def run(
         self,

integrations/docling/tests/test_converter.py

@@ -7,8 +7,9 @@
 from unittest.mock import MagicMock
 
 import pytest
+from docling.chunking import HybridChunker
+from docling.document_converter import DocumentConverter
 from docling_core.types.io import DocumentStream
-from haystack.core.serialization import component_from_dict, component_to_dict
 from haystack.dataclasses import ByteStream
 
 from haystack_integrations.components.converters.docling import (
@@ -134,8 +135,6 @@ def test_run_json_minimal() -> None:
 
 
 def test_legacy_import_path() -> None:
-    import warnings
-
     with warnings.catch_warnings(record=True) as caught:
         warnings.simplefilter("always")
         from docling_haystack.converter import DoclingConverter as LegacyDoclingConverter
@@ -146,63 +145,59 @@ def test_legacy_import_path() -> None:
     )
 
 
-def test_component_from_dict_legacy_nulls() -> None:
-    # Before the public-attribute refactor, default serialization couldn't find
-    # the _-prefixed attributes and fell back to the init defaults, so
-    # convert_kwargs and md_export_kwargs were always serialized as null.
-    # Verify that such a serialized dict still deserializes correctly.
-    legacy_data = {
+def test_component_to_dict_defaults() -> None:
+    converter = DoclingConverter()
+    assert converter.to_dict() == {
         "type": "haystack_integrations.components.converters.docling.converter.DoclingConverter",
         "init_parameters": {
             "converter": None,
-            "convert_kwargs": None,
+            "convert_kwargs": {},
             "export_type": "doc_chunks",
-            "md_export_kwargs": None,
+            "md_export_kwargs": {"image_placeholder": ""},
             "chunker": None,
             "meta_extractor": None,
         },
     }
-    restored = component_from_dict(DoclingConverter, legacy_data, "docling_converter")
-
-    assert restored.convert_kwargs == {}
-    assert restored.md_export_kwargs == {"image_placeholder": ""}
-    assert restored.export_type == ExportType.DOC_CHUNKS
-    assert restored.converter is None
-    assert restored.chunker is None
-    assert restored.meta_extractor is None
-
-
-def test_component_to_dict_defaults() -> None:
-    converter = DoclingConverter()
-    data = component_to_dict(converter, "docling_converter")
-
-    init_params = data["init_parameters"]
-    assert init_params["converter"] is None
-    assert init_params["convert_kwargs"] == {}
-    assert init_params["export_type"] == ExportType.DOC_CHUNKS
-    assert init_params["md_export_kwargs"] == {"image_placeholder": ""}
-    assert init_params["chunker"] is None
-    assert init_params["meta_extractor"] is None
 
 
 def test_component_to_dict_custom_params() -> None:
     converter = DoclingConverter(
+        converter=DocumentConverter(),
         convert_kwargs={"raises_on_error": False},
         export_type=ExportType.MARKDOWN,
         md_export_kwargs={"image_placeholder": "[img]"},
+        meta_extractor=MetaExtractor(),
     )
-    data = component_to_dict(converter, "docling_converter")
-
-    init_params = data["init_parameters"]
-    assert init_params["convert_kwargs"] == {"raises_on_error": False}
-    assert init_params["export_type"] == ExportType.MARKDOWN
-    assert init_params["md_export_kwargs"] == {"image_placeholder": "[img]"}
+    assert converter.to_dict() == {
+        "type": "haystack_integrations.components.converters.docling.converter.DoclingConverter",
+        "init_parameters": {
+            "converter": None,
+            "convert_kwargs": {"raises_on_error": False},
+            "export_type": "markdown",
+            "md_export_kwargs": {"image_placeholder": "[img]"},
+            "chunker": None,
+            "meta_extractor": {
+                "type": "haystack_integrations.components.converters.docling.converter.MetaExtractor",
+                "data": {},
+            },
+        },
+    }
 
 
 def test_component_from_dict_defaults() -> None:
-    converter = DoclingConverter()
-    data = component_to_dict(converter, "docling_converter")
-    restored = component_from_dict(DoclingConverter, data, "docling_converter")
+    # null kwargs mirror the pre-refactor serialization format and must still deserialize correctly
+    data = {
+        "type": "haystack_integrations.components.converters.docling.converter.DoclingConverter",
+        "init_parameters": {
+            "converter": None,
+            "convert_kwargs": None,
+            "export_type": "doc_chunks",
+            "md_export_kwargs": None,
+            "chunker": None,
+            "meta_extractor": None,
+        },
+    }
+    restored = DoclingConverter.from_dict(data)
 
     assert restored.converter is None
     assert restored.convert_kwargs == {}
@@ -213,17 +208,44 @@ def test_component_from_dict_defaults() -> None:
 
 
 def test_component_from_dict_custom_params() -> None:
-    converter = DoclingConverter(
-        convert_kwargs={"raises_on_error": False},
-        export_type=ExportType.JSON,
-        md_export_kwargs={"image_placeholder": "[img]"},
-    )
-    data = component_to_dict(converter, "docling_converter")
-    restored = component_from_dict(DoclingConverter, data, "docling_converter")
+    data = {
+        "type": "haystack_integrations.components.converters.docling.converter.DoclingConverter",
+        "init_parameters": {
+            "converter": None,
+            "convert_kwargs": {"raises_on_error": False},
+            "export_type": "json",
+            "md_export_kwargs": {"image_placeholder": "[img]"},
+            "chunker": None,
+            "meta_extractor": {
+                "type": "haystack_integrations.components.converters.docling.converter.MetaExtractor",
+                "data": {},
+            },
+        },
+    }
+    restored = DoclingConverter.from_dict(data)
 
+    assert restored.converter is None
     assert restored.convert_kwargs == {"raises_on_error": False}
     assert restored.export_type == ExportType.JSON
     assert restored.md_export_kwargs == {"image_placeholder": "[img]"}
+    assert restored.chunker is None
+    assert isinstance(restored.meta_extractor, MetaExtractor)
+
+
+def test_component_to_dict_chunker_warns_and_is_dropped() -> None:
+    converter = DoclingConverter(chunker=HybridChunker(merge_peers=False))
+
+    assert converter.to_dict() == {
+        "type": "haystack_integrations.components.converters.docling.converter.DoclingConverter",
+        "init_parameters": {
+            "converter": None,
+            "convert_kwargs": {},
+            "export_type": "doc_chunks",
+            "md_export_kwargs": {"image_placeholder": ""},
+            "chunker": None,
+            "meta_extractor": None,
+        },
+    }
 
 
 def test_run_with_sources_parameter() -> None: