docarray · JoanFM · Jun 16, 2023 · Jun 16, 2023 · Jun 16, 2023 · Jun 16, 2023
diff --git a/docarray/base_doc/mixins/io.py b/docarray/base_doc/mixins/io.py
@@ -12,6 +12,8 @@
     Tuple,
     Type,
     TypeVar,
+    Union,
+    get_origin,
 )
 
 import numpy as np
@@ -286,9 +288,18 @@ def _get_content_from_node_proto(
                 raise ValueError(
                     'field_type cannot be None when trying to deserialize a BaseDoc'
                 )
-            return_field = field_type.from_protobuf(
-                getattr(value, content_key)
-            )  # we get to the parent class
+            try:
+                return_field = field_type.from_protobuf(
+                    getattr(value, content_key)
+                )  # we get to the parent class
+            except Exception:
+                if get_origin(field_type) is Union:
+                    raise ValueError(
+                        'Union type is not supported for proto deserialization. Please use JSON serialization instead'
+                    )
+                raise ValueError(
+                    f'{field_type} is not supported for proto deserialization'
+                )
         elif content_key == 'doc_array':
             if field_name is None:
                 raise ValueError(

diff --git a/docarray/helper.py b/docarray/helper.py
@@ -15,6 +15,8 @@
     Union,
 )
 
+from docarray.utils._internal._typing import safe_issubclass
+
 if TYPE_CHECKING:
     from docarray import BaseDoc
 
@@ -147,9 +149,9 @@ def _get_field_type_by_access_path(
             return doc_type._get_field_type(field)
         else:
             d = doc_type._get_field_type(field)
-            if issubclass(d, DocList):
+            if safe_issubclass(d, DocList):
                 return _get_field_type_by_access_path(d.doc_type, remaining)
-            elif issubclass(d, BaseDoc):
+            elif safe_issubclass(d, BaseDoc):
                 return _get_field_type_by_access_path(d, remaining)
             else:
                 return None

diff --git a/docarray/utils/_internal/_typing.py b/docarray/utils/_internal/_typing.py
@@ -1,4 +1,4 @@
-from typing import Any, ForwardRef, Optional
+from typing import Any, ForwardRef, Optional, Union
 
 from typing_extensions import get_origin
 from typing_inspect import get_args, is_typevar, is_union_type
@@ -47,7 +47,7 @@ def safe_issubclass(x: type, a_tuple: type) -> bool:
              Note that if the origin of 'x' is a list or tuple, the function immediately returns 'False'.
     """
     if (
-        (get_origin(x) in (list, tuple, dict, set))
+        (get_origin(x) in (list, tuple, dict, set, Union))
         or is_typevar(x)
         or (type(x) == ForwardRef)
         or is_typevar(x)

diff --git a/docs/user_guide/sending/serialization.md b/docs/user_guide/sending/serialization.md
@@ -303,4 +303,8 @@ assert dv_from_proto_numpy.tensor_type == NdArray
 assert isinstance(dv_from_proto_numpy.tensor, NdArray)
 ```
 
+!!! note
+    Serialization to protobuf is not supported for union types involving `BaseDoc` types.
+
+
 
diff --git a/tests/units/array/test_array_from_to_bytes.py b/tests/units/array/test_array_from_to_bytes.py
@@ -69,3 +69,24 @@ def test_from_to_base64(protocol, compress, show_progress):
         assert d1.image.url == d2.image.url
     assert da[1].image.url is None
     assert da2[1].image.url is None
+
+
+def test_union_type_error(tmp_path):
+    from typing import Union
+
+    from docarray.documents import TextDoc
+
+    class CustomDoc(BaseDoc):
+        ud: Union[TextDoc, ImageDoc] = TextDoc(text='union type')
+
+    docs = DocList[CustomDoc]([CustomDoc(ud=TextDoc(text='union type'))])
+
+    with pytest.raises(ValueError):
+        docs.from_bytes(docs.to_bytes())
+
+    class BasisUnion(BaseDoc):
+        ud: Union[int, str]
+
+    docs_basic = DocList[BasisUnion]([BasisUnion(ud="hello")])
+    docs_copy = DocList[BasisUnion].from_bytes(docs_basic.to_bytes())
+    assert docs_copy == docs_basic
diff --git a/tests/units/array/test_array_from_to_csv.py b/tests/units/array/test_array_from_to_csv.py
@@ -120,3 +120,26 @@ class Book(BaseDoc):
     tmp_file = str(tmpdir / 'tmp.csv')
     with pytest.raises(TypeError):
         docs.to_csv(tmp_file)
+
+
+def test_union_type_error(tmp_path):
+    from typing import Union
+
+    from docarray.documents import TextDoc
+
+    class CustomDoc(BaseDoc):
+        ud: Union[TextDoc, ImageDoc] = TextDoc(text='union type')
+
+    docs = DocList[CustomDoc]([CustomDoc(ud=TextDoc(text='union type'))])
+
+    with pytest.raises(ValueError):
+        docs.to_csv(str(tmp_path) + ".csv")
+        DocList[CustomDoc].from_csv(str(tmp_path) + ".csv")
+
+    class BasisUnion(BaseDoc):
+        ud: Union[int, str]
+
+    docs_basic = DocList[BasisUnion]([BasisUnion(ud="hello")])
+    docs_basic.to_csv(str(tmp_path) + ".csv")
+    docs_copy = DocList[BasisUnion].from_csv(str(tmp_path) + ".csv")
+    assert docs_copy == docs_basic
diff --git a/tests/units/array/test_array_from_to_json.py b/tests/units/array/test_array_from_to_json.py
@@ -28,3 +28,17 @@ def test_from_to_json():
         assert d1.image.url == d2.image.url
     assert da[1].image.url is None
     assert da2[1].image.url is None
+
+
+def test_union_type():
+    from typing import Union
+
+    from docarray.documents import TextDoc
+
+    class CustomDoc(BaseDoc):
+        ud: Union[TextDoc, ImageDoc] = TextDoc(text='union type')
+
+    docs = DocList[CustomDoc]([CustomDoc(ud=TextDoc(text='union type'))])
+
+    docs_copy = docs.from_json(docs.to_json())
+    assert docs == docs_copy
diff --git a/tests/units/array/test_array_from_to_pandas.py b/tests/units/array/test_array_from_to_pandas.py
@@ -99,3 +99,25 @@ class Book(BaseDoc):
     docs = DocList([Book(title='hello'), Book(title='world')])
     with pytest.raises(TypeError):
         docs.to_dataframe()
+
+
+@pytest.mark.proto
+def test_union_type_error():
+    from typing import Union
+
+    from docarray.documents import TextDoc
+
+    class CustomDoc(BaseDoc):
+        ud: Union[TextDoc, ImageDoc] = TextDoc(text='union type')
+
+    docs = DocList[CustomDoc]([CustomDoc(ud=TextDoc(text='union type'))])
+
+    with pytest.raises(ValueError):
+        DocList[CustomDoc].from_dataframe(docs.to_dataframe())
+
+    class BasisUnion(BaseDoc):
+        ud: Union[int, str]
+
+    docs_basic = DocList[BasisUnion]([BasisUnion(ud="hello")])
+    docs_copy = DocList[BasisUnion].from_dataframe(docs_basic.to_dataframe())
+    assert docs_copy == docs_basic
diff --git a/tests/units/array/test_array_proto.py b/tests/units/array/test_array_proto.py
@@ -91,3 +91,23 @@ class ResultTestDoc(BaseDoc):
     assert docs[0].matches[0].id == '0'
     assert len(docs[0].matches) == 2
     assert len(docs) == 1
+
+
+@pytest.mark.proto
+def test_union_type_error():
+    from typing import Union
+
+    class CustomDoc(BaseDoc):
+        ud: Union[TextDoc, ImageDoc] = TextDoc(text='union type')
+
+    docs = DocList[CustomDoc]([CustomDoc(ud=TextDoc(text='union type'))])
+
+    with pytest.raises(ValueError):
+        DocList[CustomDoc].from_protobuf(docs.to_protobuf())
+
+    class BasisUnion(BaseDoc):
+        ud: Union[int, str]
+
+    docs_basic = DocList[BasisUnion]([BasisUnion(ud="hello")])
+    docs_copy = DocList[BasisUnion].from_protobuf(docs_basic.to_protobuf())
+    assert docs_copy == docs_basic