Raise ValidationError for unhashable discriminator values

changes/4773-kurtmckee.md

@@ -0,0 +1 @@
+Raise `ValidationError`, not `ConfigError`, when a discriminator value is unhashable.

pydantic/fields.py

@@ -1117,15 +1117,18 @@ def _validate_discriminated_union(
             except (AttributeError, TypeError):
                 return v, ErrorWrapper(MissingDiscriminator(discriminator_key=self.discriminator_key), loc)
 
-        try:
-            sub_field = self.sub_fields_mapping[discriminator_value]  # type: ignore[index]
-        except TypeError:
+        if self.sub_fields_mapping is None:
             assert cls is not None
             raise ConfigError(
                 f'field "{self.name}" not yet prepared so type is still a ForwardRef, '
                 f'you might need to call {cls.__name__}.update_forward_refs().'
             )
-        except KeyError:
+
+        try:
+            sub_field = self.sub_fields_mapping[discriminator_value]  # type: ignore[index]
+        except (KeyError, TypeError):
+            # KeyError: `discriminator_value` is not in the dictionary.
+            # TypeError: `discriminator_value` is unhashable.
             assert self.sub_fields_mapping is not None
             return v, ErrorWrapper(
                 InvalidDiscriminator(

tests/test_discrimated_union.py

@@ -423,3 +423,21 @@ class Container(GenericModel, Generic[T]):
 
     # coercion is done properly
     assert Container[str].parse_obj({'result': {'type': 'Success', 'data': 1}}).result.data == '1'
+
+
+def test_discriminator_with_unhashable_type():
+    """Verify an unhashable discriminator value raises a ValidationError."""
+
+    class Model1(BaseModel):
+        target: Literal['t1']
+        a: int
+
+    class Model2(BaseModel):
+        target: Literal['t2']
+        b: int
+
+    class Foo(BaseModel):
+        foo: Union[Model1, Model2] = Field(discriminator='target')
+
+    with pytest.raises(ValidationError, match=re.escape("No match for discriminator 'target' and value {}")):
+        Foo(**{'foo': {'target': {}}})