Commit eb3d7ae3

@@ -66,7 +66,7 @@ from ._compat import (
 from ._constants import RAW_RESPONSE_HEADER
 
 if TYPE_CHECKING:
-    from pydantic_core.core_schema import ModelField, LiteralSchema, ModelFieldsSchema
+    from pydantic_core.core_schema import ModelField, ModelSchema, LiteralSchema, ModelFieldsSchema
 
 __all__ = ["BaseModel", "GenericModel"]
 
@@ -671,15 +671,18 @@ def _build_discriminated_union_meta(*, union: type, meta_annotations: tuple[Any,
 
 def _extract_field_schema_pv2(model: type[BaseModel], field_name: str) -> ModelField | None:
     schema = model.__pydantic_core_schema__
+    if schema["type"] == "definitions":
+        schema = schema["schema"]
+
     if schema["type"] != "model":
         return None
 
+    schema = cast("ModelSchema", schema)
     fields_schema = schema["schema"]
     if fields_schema["type"] != "model-fields":
         return None
 
     fields_schema = cast("ModelFieldsSchema", fields_schema)
-
     field = fields_schema["fields"].get(field_name)
     if not field:
         return None

@@ -854,3 +854,35 @@ def test_field_named_cls() -> None:
     m = construct_type(value={"cls": "foo"}, type_=Model)
     assert isinstance(m, Model)
     assert isinstance(m.cls, str)
+
+
+def test_discriminated_union_case() -> None:
+    class A(BaseModel):
+        type: Literal["a"]
+
+        data: bool
+
+    class B(BaseModel):
+        type: Literal["b"]
+
+        data: List[Union[A, object]]
+
+    class ModelA(BaseModel):
+        type: Literal["modelA"]
+
+        data: int
+
+    class ModelB(BaseModel):
+        type: Literal["modelB"]
+
+        required: str
+
+        data: Union[A, B]
+
+    # when constructing ModelA | ModelB, value data doesn't match ModelB exactly - missing `required`
+    m = construct_type(
+        value={"type": "modelB", "data": {"type": "a", "data": True}},
+        type_=cast(Any, Annotated[Union[ModelA, ModelB], PropertyInfo(discriminator="type")]),
+    )
+
+    assert isinstance(m, ModelB)