Fix url serialization for unions (#11233)

sydney-runkle · web-flow · commit 6e585f925e25 · 2025-01-08T11:06:32.000-05:00
diff --git a/pydantic/networks.py b/pydantic/networks.py
@@ -10,7 +10,13 @@
 from ipaddress import IPv4Address, IPv4Interface, IPv4Network, IPv6Address, IPv6Interface, IPv6Network
 from typing import TYPE_CHECKING, Any, ClassVar
 
-from pydantic_core import MultiHostHost, PydanticCustomError, SchemaSerializer, core_schema
+from pydantic_core import (
+    MultiHostHost,
+    PydanticCustomError,
+    PydanticSerializationUnexpectedValue,
+    SchemaSerializer,
+    core_schema,
+)
 from pydantic_core import MultiHostUrl as _CoreMultiHostUrl
 from pydantic_core import Url as _CoreUrl
 from typing_extensions import Annotated, Self, TypeAlias
@@ -283,6 +289,14 @@ def build(
             )
         )
 
+    @classmethod
+    def serialize_url(cls, url: Any) -> str:
+        if not isinstance(url, cls):
+            raise PydanticSerializationUnexpectedValue(
+                f"Expected `{cls}` but got `{type(url)}` with value `'{url}'` - serialized value may not be as expected."
+            )
+        return str(url)
+
     @classmethod
     def __get_pydantic_core_schema__(
         cls, source: type[_BaseUrl], handler: GetCoreSchemaHandler
@@ -300,7 +314,7 @@ def wrap_val(v, h):
         return core_schema.no_info_wrap_validator_function(
             wrap_val,
             schema=core_schema.url_schema(**cls._constraints.defined_constraints),
-            serialization=core_schema.to_string_ser_schema(),
+            serialization=core_schema.plain_serializer_function_ser_schema(cls.serialize_url),
         )
 
     @classmethod
@@ -450,6 +464,14 @@ def build(
             )
         )
 
+    @classmethod
+    def serialize_url(cls, url: Any) -> str:
+        if not isinstance(url, cls):
+            raise PydanticSerializationUnexpectedValue(
+                f"Expected `{cls}` but got `{type(url)}` with value `'{url}'` - serialized value may not be as expected."
+            )
+        return str(url)
+
     @classmethod
     def __get_pydantic_core_schema__(
         cls, source: type[_BaseMultiHostUrl], handler: GetCoreSchemaHandler
@@ -467,7 +489,7 @@ def wrap_val(v, h):
         return core_schema.no_info_wrap_validator_function(
             wrap_val,
             schema=core_schema.multi_host_url_schema(**cls._constraints.defined_constraints),
-            serialization=core_schema.to_string_ser_schema(),
+            serialization=core_schema.plain_serializer_function_ser_schema(cls.serialize_url),
         )
 
     @classmethod
diff --git a/tests/test_networks.py b/tests/test_networks.py
@@ -2,7 +2,7 @@
 from typing import Any, Union
 
 import pytest
-from pydantic_core import PydanticCustomError, Url
+from pydantic_core import PydanticCustomError, PydanticSerializationError, Url
 from typing_extensions import Annotated
 
 from pydantic import (
@@ -1180,3 +1180,12 @@ class Model(BaseModel):
 
     with pytest.raises(ValidationError, match=r'Value should have at most 45 items after validation'):
         Model(postgres='postgres://user:pass@localhost:5432/foobarbazfoo')
+
+
+def test_unexpected_ser() -> None:
+    ta = TypeAdapter(HttpUrl)
+    with pytest.raises(
+        PydanticSerializationError,
+        match="Expected `<class 'pydantic.networks.HttpUrl'>` but got `<class 'str'>` with value `'http://example.com'`",
+    ):
+        ta.dump_python('http://example.com', warnings='error')
