diff --git a/end_to_end_tests/golden-record/my_test_api_client/models/a_model.py b/end_to_end_tests/golden-record/my_test_api_client/models/a_model.py
index 5a9ba85ae..db3c56629 100644
--- a/end_to_end_tests/golden-record/my_test_api_client/models/a_model.py
+++ b/end_to_end_tests/golden-record/my_test_api_client/models/a_model.py
@@ -206,6 +206,7 @@ def to_dict(self) -> dict[str, Any]:
             not_required_nullable_model = self.not_required_nullable_model
 
         field_dict: dict[str, Any] = {}
+
         field_dict.update(
             {
                 "an_enum_value": an_enum_value,
diff --git a/end_to_end_tests/golden-record/my_test_api_client/models/body_upload_file_tests_upload_post.py b/end_to_end_tests/golden-record/my_test_api_client/models/body_upload_file_tests_upload_post.py
index f5db27451..5bc69e864 100644
--- a/end_to_end_tests/golden-record/my_test_api_client/models/body_upload_file_tests_upload_post.py
+++ b/end_to_end_tests/golden-record/my_test_api_client/models/body_upload_file_tests_upload_post.py
@@ -136,6 +136,7 @@ def to_dict(self) -> dict[str, Any]:
         field_dict: dict[str, Any] = {}
         for prop_name, prop in self.additional_properties.items():
             field_dict[prop_name] = prop.to_dict()
+
         field_dict.update(
             {
                 "some_file": some_file,
@@ -167,116 +168,88 @@ def to_dict(self) -> dict[str, Any]:
 
         return field_dict
 
-    def to_multipart(self) -> dict[str, Any]:
-        some_file = self.some_file.to_tuple()
+    def to_multipart(self) -> list[tuple[str, Any]]:
+        field_list: list[tuple[str, Any]] = []
 
-        some_required_number = (None, str(self.some_required_number).encode(), "text/plain")
+        field_list.append(("some_file", self.some_file.to_tuple()))
 
-        some_object = (None, json.dumps(self.some_object.to_dict()).encode(), "application/json")
+        field_list.append(("some_required_number", (None, str(self.some_required_number).encode(), "text/plain")))
 
-        some_nullable_object: tuple[None, bytes, str]
+        field_list.append(("some_object", (None, json.dumps(self.some_object.to_dict()).encode(), "application/json")))
 
         if isinstance(self.some_nullable_object, BodyUploadFileTestsUploadPostSomeNullableObject):
-            some_nullable_object = (None, json.dumps(self.some_nullable_object.to_dict()).encode(), "application/json")
+            field_list.append(
+                (
+                    "some_nullable_object",
+                    (None, json.dumps(self.some_nullable_object.to_dict()).encode(), "application/json"),
+                )
+            )
         else:
-            some_nullable_object = (None, str(self.some_nullable_object).encode(), "text/plain")
+            field_list.append(("some_nullable_object", (None, str(self.some_nullable_object).encode(), "text/plain")))
 
-        some_optional_file: Union[Unset, FileJsonType] = UNSET
         if not isinstance(self.some_optional_file, Unset):
-            some_optional_file = self.some_optional_file.to_tuple()
+            field_list.append(("some_optional_file", self.some_optional_file.to_tuple()))
 
-        some_string = (
-            self.some_string
-            if isinstance(self.some_string, Unset)
-            else (None, str(self.some_string).encode(), "text/plain")
-        )
+        if not isinstance(self.some_string, Unset):
+            field_list.append(("some_string", (None, str(self.some_string).encode(), "text/plain")))
 
-        a_datetime: Union[Unset, bytes] = UNSET
         if not isinstance(self.a_datetime, Unset):
-            a_datetime = self.a_datetime.isoformat().encode()
+            field_list.append(("a_datetime", self.a_datetime.isoformat().encode()))
 
-        a_date: Union[Unset, bytes] = UNSET
         if not isinstance(self.a_date, Unset):
-            a_date = self.a_date.isoformat().encode()
+            field_list.append(("a_date", self.a_date.isoformat().encode()))
 
-        some_number = (
-            self.some_number
-            if isinstance(self.some_number, Unset)
-            else (None, str(self.some_number).encode(), "text/plain")
-        )
+        if not isinstance(self.some_number, Unset):
+            field_list.append(("some_number", (None, str(self.some_number).encode(), "text/plain")))
 
-        some_nullable_number: Union[Unset, tuple[None, bytes, str]]
+        if not isinstance(self.some_nullable_number, Unset):
+            if isinstance(self.some_nullable_number, float):
+                field_list.append(
+                    ("some_nullable_number", (None, str(self.some_nullable_number).encode(), "text/plain"))
+                )
+            else:
+                field_list.append(
+                    ("some_nullable_number", (None, str(self.some_nullable_number).encode(), "text/plain"))
+                )
 
-        if isinstance(self.some_nullable_number, Unset):
-            some_nullable_number = UNSET
-        elif isinstance(self.some_nullable_number, float):
-            some_nullable_number = (None, str(self.some_nullable_number).encode(), "text/plain")
-        else:
-            some_nullable_number = (None, str(self.some_nullable_number).encode(), "text/plain")
-
-        some_int_array: Union[Unset, tuple[None, bytes, str]] = UNSET
         if not isinstance(self.some_int_array, Unset):
-            _temp_some_int_array = []
-            for some_int_array_item_data in self.some_int_array:
-                some_int_array_item: Union[None, int]
-                some_int_array_item = some_int_array_item_data
-                _temp_some_int_array.append(some_int_array_item)
-            some_int_array = (None, json.dumps(_temp_some_int_array).encode(), "application/json")
+            for some_int_array_item_element in self.some_int_array:
+                if isinstance(some_int_array_item_element, int):
+                    field_list.append(
+                        ("some_int_array", (None, str(some_int_array_item_element).encode(), "text/plain"))
+                    )
+                else:
+                    field_list.append(
+                        ("some_int_array", (None, str(some_int_array_item_element).encode(), "text/plain"))
+                    )
+
+        if not isinstance(self.some_array, Unset):
+            if isinstance(self.some_array, list):
+                for some_array_type_0_item_element in self.some_array:
+                    field_list.append(
+                        (
+                            "some_array",
+                            (None, json.dumps(some_array_type_0_item_element.to_dict()).encode(), "application/json"),
+                        )
+                    )
+            else:
+                field_list.append(("some_array", (None, str(self.some_array).encode(), "text/plain")))
 
-        some_array: Union[Unset, tuple[None, bytes, str]]
-
-        if isinstance(self.some_array, Unset):
-            some_array = UNSET
-        elif isinstance(self.some_array, list):
-            _temp_some_array = []
-            for some_array_type_0_item_data in self.some_array:
-                some_array_type_0_item = some_array_type_0_item_data.to_dict()
-                _temp_some_array.append(some_array_type_0_item)
-            some_array = (None, json.dumps(_temp_some_array).encode(), "application/json")
-        else:
-            some_array = (None, str(self.some_array).encode(), "text/plain")
-
-        some_optional_object: Union[Unset, tuple[None, bytes, str]] = UNSET
         if not isinstance(self.some_optional_object, Unset):
-            some_optional_object = (None, json.dumps(self.some_optional_object.to_dict()).encode(), "application/json")
+            field_list.append(
+                (
+                    "some_optional_object",
+                    (None, json.dumps(self.some_optional_object.to_dict()).encode(), "application/json"),
+                )
+            )
 
-        some_enum: Union[Unset, tuple[None, bytes, str]] = UNSET
         if not isinstance(self.some_enum, Unset):
-            some_enum = (None, str(self.some_enum.value).encode(), "text/plain")
+            field_list.append(("some_enum", (None, str(self.some_enum.value).encode(), "text/plain")))
 
-        field_dict: dict[str, Any] = {}
         for prop_name, prop in self.additional_properties.items():
-            field_dict[prop_name] = (None, json.dumps(prop.to_dict()).encode(), "application/json")
-        field_dict.update(
-            {
-                "some_file": some_file,
-                "some_required_number": some_required_number,
-                "some_object": some_object,
-                "some_nullable_object": some_nullable_object,
-            }
-        )
-        if some_optional_file is not UNSET:
-            field_dict["some_optional_file"] = some_optional_file
-        if some_string is not UNSET:
-            field_dict["some_string"] = some_string
-        if a_datetime is not UNSET:
-            field_dict["a_datetime"] = a_datetime
-        if a_date is not UNSET:
-            field_dict["a_date"] = a_date
-        if some_number is not UNSET:
-            field_dict["some_number"] = some_number
-        if some_nullable_number is not UNSET:
-            field_dict["some_nullable_number"] = some_nullable_number
-        if some_int_array is not UNSET:
-            field_dict["some_int_array"] = some_int_array
-        if some_array is not UNSET:
-            field_dict["some_array"] = some_array
-        if some_optional_object is not UNSET:
-            field_dict["some_optional_object"] = some_optional_object
-        if some_enum is not UNSET:
-            field_dict["some_enum"] = some_enum
+            field_list.append((prop_name, (None, json.dumps(prop.to_dict()).encode(), "application/json")))
 
-        return field_dict
+        return field_list
 
     @classmethod
     def from_dict(cls: type[T], src_dict: Mapping[str, Any]) -> T:
diff --git a/end_to_end_tests/golden-record/my_test_api_client/models/http_validation_error.py b/end_to_end_tests/golden-record/my_test_api_client/models/http_validation_error.py
index cfe0a9a0c..43009994a 100644
--- a/end_to_end_tests/golden-record/my_test_api_client/models/http_validation_error.py
+++ b/end_to_end_tests/golden-record/my_test_api_client/models/http_validation_error.py
@@ -30,6 +30,7 @@ def to_dict(self) -> dict[str, Any]:
                 detail.append(detail_item)
 
         field_dict: dict[str, Any] = {}
+
         field_dict.update({})
         if detail is not UNSET:
             field_dict["detail"] = detail
diff --git a/end_to_end_tests/golden-record/my_test_api_client/models/model_with_additional_properties_inlined.py b/end_to_end_tests/golden-record/my_test_api_client/models/model_with_additional_properties_inlined.py
index bcdbf868c..bb70f94a8 100644
--- a/end_to_end_tests/golden-record/my_test_api_client/models/model_with_additional_properties_inlined.py
+++ b/end_to_end_tests/golden-record/my_test_api_client/models/model_with_additional_properties_inlined.py
@@ -33,6 +33,7 @@ def to_dict(self) -> dict[str, Any]:
         field_dict: dict[str, Any] = {}
         for prop_name, prop in self.additional_properties.items():
             field_dict[prop_name] = prop.to_dict()
+
         field_dict.update({})
         if a_number is not UNSET:
             field_dict["a_number"] = a_number
diff --git a/end_to_end_tests/golden-record/my_test_api_client/models/model_with_union_property.py b/end_to_end_tests/golden-record/my_test_api_client/models/model_with_union_property.py
index d704baada..aa3019f97 100644
--- a/end_to_end_tests/golden-record/my_test_api_client/models/model_with_union_property.py
+++ b/end_to_end_tests/golden-record/my_test_api_client/models/model_with_union_property.py
@@ -29,6 +29,7 @@ def to_dict(self) -> dict[str, Any]:
             a_property = self.a_property.value
 
         field_dict: dict[str, Any] = {}
+
         field_dict.update({})
         if a_property is not UNSET:
             field_dict["a_property"] = a_property
diff --git a/end_to_end_tests/golden-record/my_test_api_client/models/model_with_union_property_inlined.py b/end_to_end_tests/golden-record/my_test_api_client/models/model_with_union_property_inlined.py
index 8011b7707..e2ebb7acd 100644
--- a/end_to_end_tests/golden-record/my_test_api_client/models/model_with_union_property_inlined.py
+++ b/end_to_end_tests/golden-record/my_test_api_client/models/model_with_union_property_inlined.py
@@ -34,6 +34,7 @@ def to_dict(self) -> dict[str, Any]:
             fruit = self.fruit.to_dict()
 
         field_dict: dict[str, Any] = {}
+
         field_dict.update({})
         if fruit is not UNSET:
             field_dict["fruit"] = fruit
diff --git a/end_to_end_tests/golden-record/my_test_api_client/models/post_bodies_multiple_files_body.py b/end_to_end_tests/golden-record/my_test_api_client/models/post_bodies_multiple_files_body.py
index 5f4aefccc..81707d241 100644
--- a/end_to_end_tests/golden-record/my_test_api_client/models/post_bodies_multiple_files_body.py
+++ b/end_to_end_tests/golden-record/my_test_api_client/models/post_bodies_multiple_files_body.py
@@ -30,18 +30,16 @@ def to_dict(self) -> dict[str, Any]:
 
         return field_dict
 
-    def to_multipart(self) -> dict[str, Any]:
-        a = self.a if isinstance(self.a, Unset) else (None, str(self.a).encode(), "text/plain")
+    def to_multipart(self) -> list[tuple[str, Any]]:
+        field_list: list[tuple[str, Any]] = []
 
-        field_dict: dict[str, Any] = {}
-        for prop_name, prop in self.additional_properties.items():
-            field_dict[prop_name] = (None, str(prop).encode(), "text/plain")
+        if not isinstance(self.a, Unset):
+            field_list.append(("a", (None, str(self.a).encode(), "text/plain")))
 
-        field_dict.update({})
-        if a is not UNSET:
-            field_dict["a"] = a
+        for prop_name, prop in self.additional_properties.items():
+            field_list.append((prop_name, (None, str(prop).encode(), "text/plain")))
 
-        return field_dict
+        return field_list
 
     @classmethod
     def from_dict(cls: type[T], src_dict: Mapping[str, Any]) -> T:
diff --git a/end_to_end_tests/golden-record/my_test_api_client/models/test_inline_objects_body.py b/end_to_end_tests/golden-record/my_test_api_client/models/test_inline_objects_body.py
index e03ada2ef..66b4b3dcc 100644
--- a/end_to_end_tests/golden-record/my_test_api_client/models/test_inline_objects_body.py
+++ b/end_to_end_tests/golden-record/my_test_api_client/models/test_inline_objects_body.py
@@ -21,6 +21,7 @@ def to_dict(self) -> dict[str, Any]:
         a_property = self.a_property
 
         field_dict: dict[str, Any] = {}
+
         field_dict.update({})
         if a_property is not UNSET:
             field_dict["a_property"] = a_property
diff --git a/end_to_end_tests/golden-record/my_test_api_client/models/test_inline_objects_response_200.py b/end_to_end_tests/golden-record/my_test_api_client/models/test_inline_objects_response_200.py
index 02d7888ea..37c3005c2 100644
--- a/end_to_end_tests/golden-record/my_test_api_client/models/test_inline_objects_response_200.py
+++ b/end_to_end_tests/golden-record/my_test_api_client/models/test_inline_objects_response_200.py
@@ -21,6 +21,7 @@ def to_dict(self) -> dict[str, Any]:
         a_property = self.a_property
 
         field_dict: dict[str, Any] = {}
+
         field_dict.update({})
         if a_property is not UNSET:
             field_dict["a_property"] = a_property
diff --git a/end_to_end_tests/golden-record/my_test_api_client/models/validation_error.py b/end_to_end_tests/golden-record/my_test_api_client/models/validation_error.py
index 3c8fc9d04..613e44d4e 100644
--- a/end_to_end_tests/golden-record/my_test_api_client/models/validation_error.py
+++ b/end_to_end_tests/golden-record/my_test_api_client/models/validation_error.py
@@ -27,6 +27,7 @@ def to_dict(self) -> dict[str, Any]:
         type_ = self.type_
 
         field_dict: dict[str, Any] = {}
+
         field_dict.update(
             {
                 "loc": loc,
diff --git a/end_to_end_tests/literal-enums-golden-record/my_enum_api_client/models/a_model.py b/end_to_end_tests/literal-enums-golden-record/my_enum_api_client/models/a_model.py
index 881286e74..5c3508cf5 100644
--- a/end_to_end_tests/literal-enums-golden-record/my_enum_api_client/models/a_model.py
+++ b/end_to_end_tests/literal-enums-golden-record/my_enum_api_client/models/a_model.py
@@ -52,6 +52,7 @@ def to_dict(self) -> dict[str, Any]:
                 nested_list_of_enums.append(nested_list_of_enums_item)
 
         field_dict: dict[str, Any] = {}
+
         field_dict.update(
             {
                 "an_enum_value": an_enum_value,
diff --git a/end_to_end_tests/literal-enums-golden-record/my_enum_api_client/models/post_user_list_body.py b/end_to_end_tests/literal-enums-golden-record/my_enum_api_client/models/post_user_list_body.py
index bfddb8c02..e582bd869 100644
--- a/end_to_end_tests/literal-enums-golden-record/my_enum_api_client/models/post_user_list_body.py
+++ b/end_to_end_tests/literal-enums-golden-record/my_enum_api_client/models/post_user_list_body.py
@@ -1,4 +1,3 @@
-import json
 from collections.abc import Mapping
 from typing import Any, TypeVar, Union, cast
 
@@ -94,79 +93,66 @@ def to_dict(self) -> dict[str, Any]:
 
         return field_dict
 
-    def to_multipart(self) -> dict[str, Any]:
-        an_enum_value: Union[Unset, tuple[None, bytes, str]] = UNSET
+    def to_multipart(self) -> list[tuple[str, Any]]:
+        field_list: list[tuple[str, Any]] = []
+
         if not isinstance(self.an_enum_value, Unset):
-            _temp_an_enum_value = []
-            for an_enum_value_item_data in self.an_enum_value:
-                an_enum_value_item: str = an_enum_value_item_data
-                _temp_an_enum_value.append(an_enum_value_item)
-            an_enum_value = (None, json.dumps(_temp_an_enum_value).encode(), "application/json")
+            for an_enum_value_item_element in self.an_enum_value:
+                field_list.append(("an_enum_value", (None, str(an_enum_value_item_element).encode(), "text/plain")))
 
-        an_enum_value_with_null: Union[Unset, tuple[None, bytes, str]] = UNSET
         if not isinstance(self.an_enum_value_with_null, Unset):
-            _temp_an_enum_value_with_null = []
-            for an_enum_value_with_null_item_data in self.an_enum_value_with_null:
-                an_enum_value_with_null_item: Union[None, str]
-                if isinstance(an_enum_value_with_null_item_data, str):
-                    an_enum_value_with_null_item = an_enum_value_with_null_item_data
+            for an_enum_value_with_null_item_element in self.an_enum_value_with_null:
+                if an_enum_value_with_null_item_element is None:
+                    field_list.append(
+                        (
+                            "an_enum_value_with_null",
+                            (None, str(an_enum_value_with_null_item_element).encode(), "text/plain"),
+                        )
+                    )
                 else:
-                    an_enum_value_with_null_item = an_enum_value_with_null_item_data
-                _temp_an_enum_value_with_null.append(an_enum_value_with_null_item)
-            an_enum_value_with_null = (None, json.dumps(_temp_an_enum_value_with_null).encode(), "application/json")
+                    field_list.append(
+                        (
+                            "an_enum_value_with_null",
+                            (None, str(an_enum_value_with_null_item_element).encode(), "text/plain"),
+                        )
+                    )
 
-        an_enum_value_with_only_null: Union[Unset, tuple[None, bytes, str]] = UNSET
         if not isinstance(self.an_enum_value_with_only_null, Unset):
-            _temp_an_enum_value_with_only_null = self.an_enum_value_with_only_null
-            an_enum_value_with_only_null = (
-                None,
-                json.dumps(_temp_an_enum_value_with_only_null).encode(),
-                "application/json",
-            )
+            for an_enum_value_with_only_null_item_element in self.an_enum_value_with_only_null:
+                field_list.append(
+                    (
+                        "an_enum_value_with_only_null",
+                        (None, str(an_enum_value_with_only_null_item_element).encode(), "text/plain"),
+                    )
+                )
 
-        an_allof_enum_with_overridden_default: Union[Unset, tuple[None, bytes, str]] = UNSET
         if not isinstance(self.an_allof_enum_with_overridden_default, Unset):
-            an_allof_enum_with_overridden_default = (
-                None,
-                str(self.an_allof_enum_with_overridden_default).encode(),
-                "text/plain",
+            field_list.append(
+                (
+                    "an_allof_enum_with_overridden_default",
+                    (None, str(self.an_allof_enum_with_overridden_default).encode(), "text/plain"),
+                )
             )
 
-        an_optional_allof_enum: Union[Unset, tuple[None, bytes, str]] = UNSET
         if not isinstance(self.an_optional_allof_enum, Unset):
-            an_optional_allof_enum = (None, str(self.an_optional_allof_enum).encode(), "text/plain")
+            field_list.append(
+                ("an_optional_allof_enum", (None, str(self.an_optional_allof_enum).encode(), "text/plain"))
+            )
 
-        nested_list_of_enums: Union[Unset, tuple[None, bytes, str]] = UNSET
         if not isinstance(self.nested_list_of_enums, Unset):
-            _temp_nested_list_of_enums = []
-            for nested_list_of_enums_item_data in self.nested_list_of_enums:
-                nested_list_of_enums_item = []
-                for nested_list_of_enums_item_item_data in nested_list_of_enums_item_data:
-                    nested_list_of_enums_item_item: str = nested_list_of_enums_item_item_data
-                    nested_list_of_enums_item.append(nested_list_of_enums_item_item)
-
-                _temp_nested_list_of_enums.append(nested_list_of_enums_item)
-            nested_list_of_enums = (None, json.dumps(_temp_nested_list_of_enums).encode(), "application/json")
+            for nested_list_of_enums_item_element in self.nested_list_of_enums:
+                for nested_list_of_enums_item_item_element in nested_list_of_enums_item_element:
+                    field_list.append(
+                        (
+                            "nested_list_of_enums",
+                            (None, str(nested_list_of_enums_item_item_element).encode(), "text/plain"),
+                        )
+                    )
 
-        field_dict: dict[str, Any] = {}
         for prop_name, prop in self.additional_properties.items():
-            field_dict[prop_name] = (None, str(prop).encode(), "text/plain")
-
-        field_dict.update({})
-        if an_enum_value is not UNSET:
-            field_dict["an_enum_value"] = an_enum_value
-        if an_enum_value_with_null is not UNSET:
-            field_dict["an_enum_value_with_null"] = an_enum_value_with_null
-        if an_enum_value_with_only_null is not UNSET:
-            field_dict["an_enum_value_with_only_null"] = an_enum_value_with_only_null
-        if an_allof_enum_with_overridden_default is not UNSET:
-            field_dict["an_allof_enum_with_overridden_default"] = an_allof_enum_with_overridden_default
-        if an_optional_allof_enum is not UNSET:
-            field_dict["an_optional_allof_enum"] = an_optional_allof_enum
-        if nested_list_of_enums is not UNSET:
-            field_dict["nested_list_of_enums"] = nested_list_of_enums
+            field_list.append((prop_name, (None, str(prop).encode(), "text/plain")))
 
-        return field_dict
+        return field_list
 
     @classmethod
     def from_dict(cls: type[T], src_dict: Mapping[str, Any]) -> T:
diff --git a/end_to_end_tests/test_end_to_end.py b/end_to_end_tests/test_end_to_end.py
index 5502297ff..c1e14550a 100644
--- a/end_to_end_tests/test_end_to_end.py
+++ b/end_to_end_tests/test_end_to_end.py
@@ -266,7 +266,7 @@ def test_generate_dir_already_exists():
 
 
 def test_update_integration_tests():
-    url = "https://raw.githubusercontent.com/openapi-generators/openapi-test-server/main/openapi.json"
+    url = "https://raw.githubusercontent.com/openapi-generators/openapi-test-server/main/openapi.yaml"
     source_path = Path(__file__).parent.parent / "integration-tests"
     temp_dir = Path.cwd() / "test_update_integration_tests"
     shutil.rmtree(temp_dir, ignore_errors=True)
diff --git a/integration-tests/integration_tests/models/__init__.py b/integration-tests/integration_tests/models/__init__.py
index 275cf6faa..3243b59b0 100644
--- a/integration-tests/integration_tests/models/__init__.py
+++ b/integration-tests/integration_tests/models/__init__.py
@@ -2,6 +2,7 @@
 
 from .post_body_multipart_body import PostBodyMultipartBody
 from .post_body_multipart_response_200 import PostBodyMultipartResponse200
+from .post_body_multipart_response_200_files_item import PostBodyMultipartResponse200FilesItem
 from .post_parameters_header_response_200 import PostParametersHeaderResponse200
 from .problem import Problem
 from .public_error import PublicError
@@ -9,6 +10,7 @@
 __all__ = (
     "PostBodyMultipartBody",
     "PostBodyMultipartResponse200",
+    "PostBodyMultipartResponse200FilesItem",
     "PostParametersHeaderResponse200",
     "Problem",
     "PublicError",
diff --git a/integration-tests/integration_tests/models/post_body_multipart_body.py b/integration-tests/integration_tests/models/post_body_multipart_body.py
index f2100a10e..528d862f1 100644
--- a/integration-tests/integration_tests/models/post_body_multipart_body.py
+++ b/integration-tests/integration_tests/models/post_body_multipart_body.py
@@ -1,11 +1,11 @@
 from collections.abc import Mapping
 from io import BytesIO
-from typing import Any, TypeVar, Union
+from typing import Any, TypeVar
 
 from attrs import define as _attrs_define
 from attrs import field as _attrs_field
 
-from ..types import UNSET, File, Unset
+from ..types import File
 
 T = TypeVar("T", bound="PostBodyMultipartBody")
 
@@ -15,20 +15,23 @@ class PostBodyMultipartBody:
     """
     Attributes:
         a_string (str):
-        file (File): For the sake of this test, include a file name and content type. The payload should also be valid
-            UTF-8.
-        description (Union[Unset, str]):
+        files (list[File]):
+        description (str):
     """
 
     a_string: str
-    file: File
-    description: Union[Unset, str] = UNSET
+    files: list[File]
+    description: str
     additional_properties: dict[str, Any] = _attrs_field(init=False, factory=dict)
 
     def to_dict(self) -> dict[str, Any]:
         a_string = self.a_string
 
-        file = self.file.to_tuple()
+        files = []
+        for files_item_data in self.files:
+            files_item = files_item_data.to_tuple()
+
+            files.append(files_item)
 
         description = self.description
 
@@ -37,52 +40,45 @@ def to_dict(self) -> dict[str, Any]:
         field_dict.update(
             {
                 "a_string": a_string,
-                "file": file,
+                "files": files,
+                "description": description,
             }
         )
-        if description is not UNSET:
-            field_dict["description"] = description
 
         return field_dict
 
-    def to_multipart(self) -> dict[str, Any]:
-        a_string = (None, str(self.a_string).encode(), "text/plain")
+    def to_multipart(self) -> list[tuple[str, Any]]:
+        field_list: list[tuple[str, Any]] = []
 
-        file = self.file.to_tuple()
+        field_list.append(("a_string", (None, str(self.a_string).encode(), "text/plain")))
 
-        description = (
-            self.description
-            if isinstance(self.description, Unset)
-            else (None, str(self.description).encode(), "text/plain")
-        )
+        for files_item_element in self.files:
+            field_list.append(("files", files_item_element.to_tuple()))
 
-        field_dict: dict[str, Any] = {}
-        for prop_name, prop in self.additional_properties.items():
-            field_dict[prop_name] = (None, str(prop).encode(), "text/plain")
+        field_list.append(("description", (None, str(self.description).encode(), "text/plain")))
 
-        field_dict.update(
-            {
-                "a_string": a_string,
-                "file": file,
-            }
-        )
-        if description is not UNSET:
-            field_dict["description"] = description
+        for prop_name, prop in self.additional_properties.items():
+            field_list.append((prop_name, (None, str(prop).encode(), "text/plain")))
 
-        return field_dict
+        return field_list
 
     @classmethod
     def from_dict(cls: type[T], src_dict: Mapping[str, Any]) -> T:
         d = dict(src_dict)
         a_string = d.pop("a_string")
 
-        file = File(payload=BytesIO(d.pop("file")))
+        files = []
+        _files = d.pop("files")
+        for files_item_data in _files:
+            files_item = File(payload=BytesIO(files_item_data))
+
+            files.append(files_item)
 
-        description = d.pop("description", UNSET)
+        description = d.pop("description")
 
         post_body_multipart_body = cls(
             a_string=a_string,
-            file=file,
+            files=files,
             description=description,
         )
 
diff --git a/integration-tests/integration_tests/models/post_body_multipart_response_200.py b/integration-tests/integration_tests/models/post_body_multipart_response_200.py
index 9b4862f0b..08c170dd1 100644
--- a/integration-tests/integration_tests/models/post_body_multipart_response_200.py
+++ b/integration-tests/integration_tests/models/post_body_multipart_response_200.py
@@ -1,9 +1,13 @@
 from collections.abc import Mapping
-from typing import Any, TypeVar
+from typing import TYPE_CHECKING, Any, TypeVar
 
 from attrs import define as _attrs_define
 from attrs import field as _attrs_field
 
+if TYPE_CHECKING:
+    from ..models.post_body_multipart_response_200_files_item import PostBodyMultipartResponse200FilesItem
+
+
 T = TypeVar("T", bound="PostBodyMultipartResponse200")
 
 
@@ -12,39 +16,32 @@ class PostBodyMultipartResponse200:
     """
     Attributes:
         a_string (str): Echo of the 'a_string' input parameter from the form.
-        file_data (str): Echo of content of the 'file' input parameter from the form.
         description (str): Echo of the 'description' input parameter from the form.
-        file_name (str): The name of the file uploaded.
-        file_content_type (str): The content type of the file uploaded.
+        files (list['PostBodyMultipartResponse200FilesItem']):
     """
 
     a_string: str
-    file_data: str
     description: str
-    file_name: str
-    file_content_type: str
+    files: list["PostBodyMultipartResponse200FilesItem"]
     additional_properties: dict[str, Any] = _attrs_field(init=False, factory=dict)
 
     def to_dict(self) -> dict[str, Any]:
         a_string = self.a_string
 
-        file_data = self.file_data
-
         description = self.description
 
-        file_name = self.file_name
-
-        file_content_type = self.file_content_type
+        files = []
+        for files_item_data in self.files:
+            files_item = files_item_data.to_dict()
+            files.append(files_item)
 
         field_dict: dict[str, Any] = {}
         field_dict.update(self.additional_properties)
         field_dict.update(
             {
                 "a_string": a_string,
-                "file_data": file_data,
                 "description": description,
-                "file_name": file_name,
-                "file_content_type": file_content_type,
+                "files": files,
             }
         )
 
@@ -52,23 +49,24 @@ def to_dict(self) -> dict[str, Any]:
 
     @classmethod
     def from_dict(cls: type[T], src_dict: Mapping[str, Any]) -> T:
+        from ..models.post_body_multipart_response_200_files_item import PostBodyMultipartResponse200FilesItem
+
         d = dict(src_dict)
         a_string = d.pop("a_string")
 
-        file_data = d.pop("file_data")
-
         description = d.pop("description")
 
-        file_name = d.pop("file_name")
+        files = []
+        _files = d.pop("files")
+        for files_item_data in _files:
+            files_item = PostBodyMultipartResponse200FilesItem.from_dict(files_item_data)
 
-        file_content_type = d.pop("file_content_type")
+            files.append(files_item)
 
         post_body_multipart_response_200 = cls(
             a_string=a_string,
-            file_data=file_data,
             description=description,
-            file_name=file_name,
-            file_content_type=file_content_type,
+            files=files,
         )
 
         post_body_multipart_response_200.additional_properties = d
diff --git a/integration-tests/integration_tests/models/post_body_multipart_response_200_files_item.py b/integration-tests/integration_tests/models/post_body_multipart_response_200_files_item.py
new file mode 100644
index 000000000..e30f77566
--- /dev/null
+++ b/integration-tests/integration_tests/models/post_body_multipart_response_200_files_item.py
@@ -0,0 +1,77 @@
+from collections.abc import Mapping
+from typing import Any, TypeVar, Union
+
+from attrs import define as _attrs_define
+from attrs import field as _attrs_field
+
+from ..types import UNSET, Unset
+
+T = TypeVar("T", bound="PostBodyMultipartResponse200FilesItem")
+
+
+@_attrs_define
+class PostBodyMultipartResponse200FilesItem:
+    """
+    Attributes:
+        data (Union[Unset, str]): Echo of content of the 'file' input parameter from the form.
+        name (Union[Unset, str]): The name of the file uploaded.
+        content_type (Union[Unset, str]): The content type of the file uploaded.
+    """
+
+    data: Union[Unset, str] = UNSET
+    name: Union[Unset, str] = UNSET
+    content_type: Union[Unset, str] = UNSET
+    additional_properties: dict[str, Any] = _attrs_field(init=False, factory=dict)
+
+    def to_dict(self) -> dict[str, Any]:
+        data = self.data
+
+        name = self.name
+
+        content_type = self.content_type
+
+        field_dict: dict[str, Any] = {}
+        field_dict.update(self.additional_properties)
+        field_dict.update({})
+        if data is not UNSET:
+            field_dict["data"] = data
+        if name is not UNSET:
+            field_dict["name"] = name
+        if content_type is not UNSET:
+            field_dict["content_type"] = content_type
+
+        return field_dict
+
+    @classmethod
+    def from_dict(cls: type[T], src_dict: Mapping[str, Any]) -> T:
+        d = dict(src_dict)
+        data = d.pop("data", UNSET)
+
+        name = d.pop("name", UNSET)
+
+        content_type = d.pop("content_type", UNSET)
+
+        post_body_multipart_response_200_files_item = cls(
+            data=data,
+            name=name,
+            content_type=content_type,
+        )
+
+        post_body_multipart_response_200_files_item.additional_properties = d
+        return post_body_multipart_response_200_files_item
+
+    @property
+    def additional_keys(self) -> list[str]:
+        return list(self.additional_properties.keys())
+
+    def __getitem__(self, key: str) -> Any:
+        return self.additional_properties[key]
+
+    def __setitem__(self, key: str, value: Any) -> None:
+        self.additional_properties[key] = value
+
+    def __delitem__(self, key: str) -> None:
+        del self.additional_properties[key]
+
+    def __contains__(self, key: str) -> bool:
+        return key in self.additional_properties
diff --git a/integration-tests/pyproject.toml b/integration-tests/pyproject.toml
index 536a55b32..43f1884d7 100644
--- a/integration-tests/pyproject.toml
+++ b/integration-tests/pyproject.toml
@@ -1,6 +1,6 @@
 [project]
 name = "integration-tests"
-version = "0.0.1"
+version = "0.1.0"
 description = "A client library for accessing OpenAPI Test Server"
 authors = []
 readme = "README.md"
diff --git a/integration-tests/tests/test_api/test_body/test_post_body_multipart.py b/integration-tests/tests/test_api/test_body/test_post_body_multipart.py
index 54498ebc5..6934b01ee 100644
--- a/integration-tests/tests/test_api/test_body/test_post_body_multipart.py
+++ b/integration-tests/tests/test_api/test_body/test_post_body_multipart.py
@@ -9,23 +9,29 @@
 from integration_tests.models.post_body_multipart_response_200 import PostBodyMultipartResponse200
 from integration_tests.types import File
 
+files = [
+    File(
+        payload=BytesIO(b"some file content"),
+        file_name="cool_stuff.txt",
+        mime_type="application/openapi-python-client",
+    ),
+    File(
+        payload=BytesIO(b"more file content"),
+        file_name=None,
+        mime_type=None,
+    ),
+]
+
 
 def test(client: Client) -> None:
     a_string = "a test string"
-    payload = b"some file content"
-    file_name = "cool_stuff.txt"
-    mime_type = "application/openapi-python-client"
     description = "super descriptive thing"
 
     response = post_body_multipart.sync_detailed(
         client=client,
         body=PostBodyMultipartBody(
             a_string=a_string,
-            file=File(
-                payload=BytesIO(payload),
-                file_name=file_name,
-                mime_type=mime_type,
-            ),
+            files=files,
             description=description,
         ),
     )
@@ -35,17 +41,16 @@ def test(client: Client) -> None:
         raise AssertionError(f"Received status {response.status_code} from test server with payload: {content!r}")
 
     assert content.a_string == a_string
-    assert content.file_name == file_name
-    assert content.file_content_type == mime_type
-    assert content.file_data.encode() == payload
     assert content.description == description
+    for i, file in enumerate(content.files):
+        files[i].payload.seek(0)
+        assert file.data == files[i].payload.read().decode()
+        assert file.name == files[i].file_name
+        assert file.content_type == files[i].mime_type
 
 
 def test_custom_hooks() -> None:
     a_string = "a test string"
-    payload = b"some file content"
-    file_name = "cool_stuff.txt"
-    mime_type = "application/openapi-python-client"
     description = "super descriptive thing"
 
     request_hook_called = False
@@ -67,11 +72,7 @@ def log_response(*_: Any, **__: Any) -> None:
         client=client,
         body=PostBodyMultipartBody(
             a_string=a_string,
-            file=File(
-                payload=BytesIO(payload),
-                file_name=file_name,
-                mime_type=mime_type,
-            ),
+            files=files,
             description=description,
         ),
     )
@@ -82,9 +83,6 @@ def log_response(*_: Any, **__: Any) -> None:
 
 def test_context_manager(client: Client) -> None:
     a_string = "a test string"
-    payload = b"some file content"
-    file_name = "cool_stuff.txt"
-    mime_type = "application/openapi-python-client"
     description = "super descriptive thing"
 
     with client as client:
@@ -92,11 +90,7 @@ def test_context_manager(client: Client) -> None:
             client=client,
             body=PostBodyMultipartBody(
                 a_string=a_string,
-                file=File(
-                    payload=BytesIO(payload),
-                    file_name=file_name,
-                    mime_type=mime_type,
-                ),
+                files=files,
                 description=description,
             ),
         )
@@ -104,11 +98,7 @@ def test_context_manager(client: Client) -> None:
             client=client,
             body=PostBodyMultipartBody(
                 a_string=a_string,
-                file=File(
-                    payload=BytesIO(payload),
-                    file_name=file_name,
-                    mime_type=mime_type,
-                ),
+                files=files,
                 description=description,
             ),
         )
@@ -118,11 +108,7 @@ def test_context_manager(client: Client) -> None:
             client=client,
             body=PostBodyMultipartBody(
                 a_string=a_string,
-                file=File(
-                    payload=BytesIO(payload),
-                    file_name=file_name,
-                    mime_type=mime_type,
-                ),
+                files=files,
                 description=description,
             ),
         )
@@ -131,30 +117,17 @@ def test_context_manager(client: Client) -> None:
     if not isinstance(content, PostBodyMultipartResponse200):
         raise AssertionError(f"Received status {response.status_code} from test server with payload: {content!r}")
 
-    assert content.a_string == a_string
-    assert content.file_name == file_name
-    assert content.file_content_type == mime_type
-    assert content.file_data.encode() == payload
-    assert content.description == description
-
 
 @pytest.mark.asyncio
 async def test_async(client: Client) -> None:
     a_string = "a test string"
-    payload = b"some file content"
-    file_name = "cool_stuff.txt"
-    mime_type = "application/openapi-python-client"
     description = "super descriptive thing"
 
     response = await post_body_multipart.asyncio_detailed(
         client=client,
         body=PostBodyMultipartBody(
             a_string=a_string,
-            file=File(
-                payload=BytesIO(payload),
-                file_name=file_name,
-                mime_type=mime_type,
-            ),
+            files=files,
             description=description,
         ),
     )
@@ -164,18 +137,17 @@ async def test_async(client: Client) -> None:
         raise AssertionError(f"Received status {response.status_code} from test server with payload: {content!r}")
 
     assert content.a_string == a_string
-    assert content.file_name == file_name
-    assert content.file_content_type == mime_type
-    assert content.file_data.encode() == payload
     assert content.description == description
+    for i, file in enumerate(content.files):
+        files[i].payload.seek(0)
+        assert file.data == files[i].payload.read().decode()
+        assert file.name == files[i].file_name
+        assert file.content_type == files[i].mime_type
 
 
 @pytest.mark.asyncio
 async def test_async_context_manager(client: Client) -> None:
     a_string = "a test string"
-    payload = b"some file content"
-    file_name = "cool_stuff.txt"
-    mime_type = "application/openapi-python-client"
     description = "super descriptive thing"
 
     async with client as client:
@@ -183,11 +155,7 @@ async def test_async_context_manager(client: Client) -> None:
             client=client,
             body=PostBodyMultipartBody(
                 a_string=a_string,
-                file=File(
-                    payload=BytesIO(payload),
-                    file_name=file_name,
-                    mime_type=mime_type,
-                ),
+                files=files,
                 description=description,
             ),
         )
@@ -195,11 +163,7 @@ async def test_async_context_manager(client: Client) -> None:
             client=client,
             body=PostBodyMultipartBody(
                 a_string=a_string,
-                file=File(
-                    payload=BytesIO(payload),
-                    file_name=file_name,
-                    mime_type=mime_type,
-                ),
+                files=files,
                 description=description,
             ),
         )
@@ -209,11 +173,7 @@ async def test_async_context_manager(client: Client) -> None:
             client=client,
             body=PostBodyMultipartBody(
                 a_string=a_string,
-                file=File(
-                    payload=BytesIO(payload),
-                    file_name=file_name,
-                    mime_type=mime_type,
-                ),
+                files=files,
                 description=description,
             ),
         )
@@ -223,7 +183,9 @@ async def test_async_context_manager(client: Client) -> None:
         raise AssertionError(f"Received status {response.status_code} from test server with payload: {content!r}")
 
     assert content.a_string == a_string
-    assert content.file_name == file_name
-    assert content.file_content_type == mime_type
-    assert content.file_data.encode() == payload
     assert content.description == description
+    for i, file in enumerate(content.files):
+        files[i].payload.seek(0)
+        assert file.data == files[i].payload.read().decode()
+        assert file.name == files[i].file_name
+        assert file.content_type == files[i].mime_type
diff --git a/openapi_python_client/templates/model.py.jinja b/openapi_python_client/templates/model.py.jinja
index eed2ea3a0..2f48654ec 100644
--- a/openapi_python_client/templates/model.py.jinja
+++ b/openapi_python_client/templates/model.py.jinja
@@ -82,32 +82,45 @@ class {{ class_name }}:
     additional_properties: dict[str, {{ additional_property_type }}] = _attrs_field(init=False, factory=dict)
     {% endif %}
 
-{% macro _to_dict(multipart=False) %}
-{% for property in model.required_properties + model.optional_properties %}
+{% macro _transform_property(property, content) %}
 {% import "property_templates/" + property.template as prop_template %}
-{% if multipart %}
-{{ prop_template.transform_multipart(property, "self." + property.python_name, property.python_name) }}
-{% elif prop_template.transform %}
-{{ prop_template.transform(property=property, source="self." + property.python_name, destination=property.python_name) }}
+{%- if prop_template.transform -%}
+{{ prop_template.transform(property=property, source=content, destination=property.python_name) }}
+{%- else -%}
+{{ property.python_name }} = {{ content }}
+{%- endif -%}
+{% endmacro %}
+
+{% macro multipart(property, source, destination) %}
+{% import "property_templates/" + property.template as prop_template %}
+{% if not property.required %}
+if not isinstance({{source}}, Unset):
+    {{ prop_template.multipart(property, source, destination) | indent(4) }}
 {% else %}
-{{ property.python_name }} = self.{{ property.python_name }}
+{{ prop_template.multipart(property, source, destination) }}
 {% endif %}
+{% endmacro %}
 
-{% endfor %}
-
+{% macro _prepare_field_dict() %}
 field_dict: dict[str, Any] = {}
 {% if model.additional_properties %}
 {% import "property_templates/" + model.additional_properties.template as prop_template %}
-{% if multipart %}
-for prop_name, prop in self.additional_properties.items():
-    {{ prop_template.transform_multipart(model.additional_properties, "prop", "field_dict[prop_name]") | indent(4) }}
-{% elif prop_template.transform %}
+{% if prop_template.transform %}
 for prop_name, prop in self.additional_properties.items():
     {{ prop_template.transform(model.additional_properties, "prop", "field_dict[prop_name]", declare_type=false) | indent(4) }}
 {% else %}
 field_dict.update(self.additional_properties)
-{% endif %}
-{% endif %}
+{%- endif -%}
+{%- endif -%}
+{% endmacro %}
+
+{% macro _to_dict() %}
+{% for property in model.required_properties + model.optional_properties -%}
+{{ _transform_property(property, "self." + property.python_name) }}
+
+{% endfor %}
+
+{{ _prepare_field_dict() }}
 {% if model.required_properties | length > 0 or model.optional_properties | length > 0 %}
 field_dict.update({
     {% for property in model.required_properties + model.optional_properties %}
@@ -134,8 +147,22 @@ return field_dict
         {{ _to_dict() | indent(8) }}
 
 {% if model.is_multipart_body %}
-    def to_multipart(self) -> dict[str, Any]:
-        {{ _to_dict(multipart=True) | indent(8) }}
+    def to_multipart(self) -> list[tuple[str, Any]]:
+        field_list: list[tuple[str, Any]] = []
+
+        {% for property in model.required_properties + model.optional_properties %}
+        {% set destination = "\"" + property.name + "\"" %}
+        {{ multipart(property, "self." + property.python_name, destination) | indent(8) }}
+
+        {% endfor %}
+
+        {% if model.additional_properties %}
+        for prop_name, prop in self.additional_properties.items():
+            {{ multipart(model.additional_properties, "prop", "prop_name") | indent(4) }}
+        {% endif %}
+
+        return field_list
+
 {% endif %}
 
     @classmethod
diff --git a/openapi_python_client/templates/property_templates/any_property.py.jinja b/openapi_python_client/templates/property_templates/any_property.py.jinja
index 25a16516a..0eff2d50e 100644
--- a/openapi_python_client/templates/property_templates/any_property.py.jinja
+++ b/openapi_python_client/templates/property_templates/any_property.py.jinja
@@ -1,7 +1,3 @@
-{% macro transform_multipart(property, source, destination) %}
-{% if not property.required %}
-{{ destination }} = {{source}} if isinstance({{source}}, Unset) else (None, str({{source}}).encode(), "text/plain")
-{% else %}
-{{ destination }} =  (None, str({{ source }}).encode(), "text/plain")
-{% endif %}
+{% macro multipart(property, source, destination) %}
+field_list.append(({{ destination }}, (None, str({{source}}).encode(), "text/plain")))
 {% endmacro %}
\ No newline at end of file
diff --git a/openapi_python_client/templates/property_templates/boolean_property.py.jinja b/openapi_python_client/templates/property_templates/boolean_property.py.jinja
index 52fda08e1..b9a837e9c 100644
--- a/openapi_python_client/templates/property_templates/boolean_property.py.jinja
+++ b/openapi_python_client/templates/property_templates/boolean_property.py.jinja
@@ -2,10 +2,6 @@
 "true" if {{ source }} else "false"
 {% endmacro %}
 
-{% macro transform_multipart(property, source, destination) %}
-{% if not property.required %}
-{{ destination }} = {{source}} if isinstance({{source}}, Unset) else (None, str({{source}}).encode(), "text/plain")
-{% else %}
-{{ destination }} =  (None, str({{ source }}).encode(), "text/plain")
-{% endif %}
+{% macro multipart(property, source, destination) %}
+field_list.append(({{ destination }}, (None, str({{source}}).encode(), "text/plain")))
 {% endmacro %}
diff --git a/openapi_python_client/templates/property_templates/const_property.py.jinja b/openapi_python_client/templates/property_templates/const_property.py.jinja
index fa635b5b9..8ad5bbff9 100644
--- a/openapi_python_client/templates/property_templates/const_property.py.jinja
+++ b/openapi_python_client/templates/property_templates/const_property.py.jinja
@@ -3,3 +3,7 @@
 if {{ property.python_name }} != {{ property.value.python_code }}{% if not property.required %}and not isinstance({{ property.python_name }}, Unset){% endif %}:
     raise ValueError(f"{{ property.name }} must match const {{ property.value.python_code }}, got '{{'{' + property.python_name + '}' }}'")
 {%- endmacro %}
+
+{% macro multipart(property, source, destination) %}
+field_list.append(({{ destination }}, source))
+{% endmacro %}
diff --git a/openapi_python_client/templates/property_templates/date_property.py.jinja b/openapi_python_client/templates/property_templates/date_property.py.jinja
index b5da665f7..bf88444fe 100644
--- a/openapi_python_client/templates/property_templates/date_property.py.jinja
+++ b/openapi_python_client/templates/property_templates/date_property.py.jinja
@@ -26,14 +26,7 @@ if not isinstance({{ source }}, Unset):
 {%- endif %}
 {% endmacro %}
 
-{% macro transform_multipart(property, source, destination) %}
+{% macro multipart(property, source, destination) %}
 {% set transformed = source + ".isoformat().encode()" %}
-{% if property.required %}
-{{ destination }} = {{ transformed }}
-{%- else %}
-{% set type_annotation = property.get_type_string(json=True) | replace("str", "bytes") %}
-{{ destination }}: {{ type_annotation }} = UNSET
-if not isinstance({{ source }}, Unset):
-    {{ destination }} = {{ transformed }}
-{%- endif %}
+field_list.append(({{ destination }}, {{ transformed }}))
 {% endmacro %}
diff --git a/openapi_python_client/templates/property_templates/datetime_property.py.jinja b/openapi_python_client/templates/property_templates/datetime_property.py.jinja
index 32e3f2ee6..29c38bc97 100644
--- a/openapi_python_client/templates/property_templates/datetime_property.py.jinja
+++ b/openapi_python_client/templates/property_templates/datetime_property.py.jinja
@@ -26,14 +26,7 @@ if not isinstance({{ source }}, Unset):
 {%- endif %}
 {% endmacro %}
 
-{% macro transform_multipart(property, source, destination) %}
+{% macro multipart(property, source, destination) %}
 {% set transformed = source + ".isoformat().encode()" %}
-{% if property.required %}
-{{ destination }} = {{ transformed }}
-{%- else %}
-{% set type_annotation = property.get_type_string(json=True) | replace("str", "bytes") %}
-{{ destination }}: {{ type_annotation }} = UNSET
-if not isinstance({{ source }}, Unset):
-    {{ destination }} = {{ transformed }}
-{%- endif %}
+field_list.append(({{ destination }}, {{ transformed }}))
 {% endmacro %}
diff --git a/openapi_python_client/templates/property_templates/enum_property.py.jinja b/openapi_python_client/templates/property_templates/enum_property.py.jinja
index c46538eac..aac89aeac 100644
--- a/openapi_python_client/templates/property_templates/enum_property.py.jinja
+++ b/openapi_python_client/templates/property_templates/enum_property.py.jinja
@@ -22,16 +22,9 @@ if not isinstance({{ source }}, Unset):
 {% endif %}
 {% endmacro %}
 
-{% macro transform_multipart(property, source, destination) %}
+{% macro multipart(property, source, destination) %}
 {% set transformed = "(None, str(" + source + ".value" + ").encode(), \"text/plain\")" %}
-{% set type_string = "Union[Unset, tuple[None, bytes, str]]" %}
-{% if property.required %}
-{{ destination }} = {{ transformed }}
-{%- else %}
-{{ destination }}: {{ type_string }} = UNSET
-if not isinstance({{ source }}, Unset):
-    {{ destination }} = {{ transformed }}
-{% endif %}
+field_list.append(({{ destination }}, {{ transformed }}))
 {% endmacro %}
 
 {% macro transform_header(source) %}
diff --git a/openapi_python_client/templates/property_templates/file_property.py.jinja b/openapi_python_client/templates/property_templates/file_property.py.jinja
index 8d27ae617..275650db3 100644
--- a/openapi_python_client/templates/property_templates/file_property.py.jinja
+++ b/openapi_python_client/templates/property_templates/file_property.py.jinja
@@ -22,12 +22,6 @@ if not isinstance({{ source }}, Unset):
 {% endif %}
 {% endmacro %}
 
-{% macro transform_multipart(property, source, destination) %}
-{% if property.required %}
-{{ destination }} = {{ source }}.to_tuple()
-{% else %}
-{{ destination }}: {{ property.get_type_string(json=True) }} = UNSET
-if not isinstance({{ source }}, Unset):
-    {{ destination }} = {{ source }}.to_tuple()
-{% endif %}
+{% macro multipart(property, source, destination) %}
+field_list.append(({{ destination }}, {{ source }}.to_tuple()))
 {% endmacro %}
diff --git a/openapi_python_client/templates/property_templates/float_property.py.jinja b/openapi_python_client/templates/property_templates/float_property.py.jinja
index 12ffb0fb4..0729c82fb 100644
--- a/openapi_python_client/templates/property_templates/float_property.py.jinja
+++ b/openapi_python_client/templates/property_templates/float_property.py.jinja
@@ -2,10 +2,6 @@
 str({{ source }})
 {% endmacro %}
 
-{% macro transform_multipart(property, source, destination) %}
-{% if not property.required %}
-{{ destination }} = {{source}} if isinstance({{source}}, Unset) else (None, str({{source}}).encode(), "text/plain")
-{% else %}
-{{ destination }} =  (None, str({{ source }}).encode(), "text/plain")
-{% endif %}
+{% macro multipart(property, source, destination) %}
+field_list.append(({{ destination }}, (None, str({{source}}).encode(), "text/plain")))
 {% endmacro %}
diff --git a/openapi_python_client/templates/property_templates/int_property.py.jinja b/openapi_python_client/templates/property_templates/int_property.py.jinja
index 12ffb0fb4..0729c82fb 100644
--- a/openapi_python_client/templates/property_templates/int_property.py.jinja
+++ b/openapi_python_client/templates/property_templates/int_property.py.jinja
@@ -2,10 +2,6 @@
 str({{ source }})
 {% endmacro %}
 
-{% macro transform_multipart(property, source, destination) %}
-{% if not property.required %}
-{{ destination }} = {{source}} if isinstance({{source}}, Unset) else (None, str({{source}}).encode(), "text/plain")
-{% else %}
-{{ destination }} =  (None, str({{ source }}).encode(), "text/plain")
-{% endif %}
+{% macro multipart(property, source, destination) %}
+field_list.append(({{ destination }}, (None, str({{source}}).encode(), "text/plain")))
 {% endmacro %}
diff --git a/openapi_python_client/templates/property_templates/list_property.py.jinja b/openapi_python_client/templates/property_templates/list_property.py.jinja
index 94a9c6d65..fc68cb2ec 100644
--- a/openapi_python_client/templates/property_templates/list_property.py.jinja
+++ b/openapi_python_client/templates/property_templates/list_property.py.jinja
@@ -17,12 +17,8 @@ for {{ inner_source }} in (_{{ property.python_name }} or []):
 {% endif %}
 {% endmacro %}
 
-{% macro _transform(property, source, destination, multipart, transform_method) %}
+{% macro _transform(property, source, destination, transform_method) %}
 {% set inner_property = property.inner_property %}
-{% if multipart %}
-{% set multipart_destination = destination %}
-{% set destination = "_temp_" + destination %}
-{% endif %}
 {% import "property_templates/" + inner_property.template as inner_template %}
 {% if inner_template.transform %}
 {% set inner_source = inner_property.python_name + "_data" %}
@@ -33,9 +29,6 @@ for {{ inner_source }} in {{ source }}:
 {% else %}
 {{ destination }} = {{ source }}
 {% endif %}
-{% if multipart %}
-{{ multipart_destination }} = (None, json.dumps({{ destination }}).encode(), 'application/json')
-{% endif %}
 {% endmacro %}
 
 {% macro check_type_for_construct(property, source) %}isinstance({{ source }}, list){% endmacro %}
@@ -44,34 +37,30 @@ for {{ inner_source }} in {{ source }}:
 {% set inner_property = property.inner_property %}
 {% set type_string = property.get_type_string(json=True) %}
 {% if property.required %}
-{{ _transform(property, source, destination, False, "to_dict") }}
+{{ _transform(property, source, destination, "to_dict") }}
 {% else %}
 {{ destination }}{% if declare_type %}: {{ type_string }}{% endif %} = UNSET
 if not isinstance({{ source }}, Unset):
-    {{ _transform(property, source, destination, False, "to_dict") | indent(4)}}
+    {{ _transform(property, source, destination, "to_dict") | indent(4)}}
 {% endif %}
 {% endmacro %}
 
-{% macro transform_multipart(property, source, destination) %}
+{% macro transform_multipart_body(property, source, destination) %}
 {% set inner_property = property.inner_property %}
-{% set type_string = "Union[Unset, tuple[None, bytes, str]]" %}
+{% set type_string = property.get_type_string(json=True) %}
 {% if property.required %}
-{{ _transform(property, source, destination, True, "to_dict") }}
+{{ _transform(property, source, destination, "to_multipart") }}
 {% else %}
 {{ destination }}: {{ type_string }} = UNSET
 if not isinstance({{ source }}, Unset):
-    {{ _transform(property, source, destination, True, "to_dict") | indent(4)}}
+    {{ _transform(property, source, destination, "to_multipart") | indent(4)}}
 {% endif %}
 {% endmacro %}
 
-{% macro transform_multipart_body(property, source, destination) %}
+{% macro multipart(property, source, destination) %}
 {% set inner_property = property.inner_property %}
-{% set type_string = property.get_type_string(json=True) %}
-{% if property.required %}
-{{ _transform(property, source, destination, False, "to_multipart") }}
-{% else %}
-{{ destination }}: {{ type_string }} = UNSET
-if not isinstance({{ source }}, Unset):
-    {{ _transform(property, source, destination, False, "to_multipart") | indent(4)}}
-{% endif %}
+{% import "property_templates/" + inner_property.template as inner_template %}
+{% set inner_source = inner_property.python_name + "_element" %}
+for {{ inner_source }} in {{ source }}:
+    {{ inner_template.multipart(inner_property, inner_source, destination) | indent(4) }}
 {% endmacro %}
diff --git a/openapi_python_client/templates/property_templates/literal_enum_property.py.jinja b/openapi_python_client/templates/property_templates/literal_enum_property.py.jinja
index 1506284d7..442d102ea 100644
--- a/openapi_python_client/templates/property_templates/literal_enum_property.py.jinja
+++ b/openapi_python_client/templates/property_templates/literal_enum_property.py.jinja
@@ -21,16 +21,9 @@ if not isinstance({{ source }}, Unset):
 {% endif %}
 {% endmacro %}
 
-{% macro transform_multipart(property, source, destination) %}
+{% macro multipart(property, source, destination) %}
 {% set transformed = "(None, str(" + source + ").encode(), \"text/plain\")" %}
-{% set type_string = "Union[Unset, tuple[None, bytes, str]]" %}
-{% if property.required %}
-{{ destination }} = {{ transformed }}
-{%- else %}
-{{ destination }}: {{ type_string }} = UNSET
-if not isinstance({{ source }}, Unset):
-    {{ destination }} = {{ transformed }}
-{% endif %}
+field_list.append(({{ destination }}, {{ transformed }}))
 {% endmacro %}
 
 {% macro transform_header(source) %}
diff --git a/openapi_python_client/templates/property_templates/model_property.py.jinja b/openapi_python_client/templates/property_templates/model_property.py.jinja
index 308b7478b..fbc517b43 100644
--- a/openapi_python_client/templates/property_templates/model_property.py.jinja
+++ b/openapi_python_client/templates/property_templates/model_property.py.jinja
@@ -34,14 +34,7 @@ if not isinstance({{ source }}, Unset):
 {%- endif %}
 {% endmacro %}
 
-{% macro transform_multipart(property, source, destination) %}
+{% macro multipart(property, source, destination) %}
 {% set transformed = "(None, json.dumps(" + source + ".to_dict()" + ").encode(), 'application/json')" %}
-{% set type_string = property.get_type_string(multipart=True) %}
-{% if property.required %}
-{{ destination }} = {{ transformed }}
-{%- else %}
-{{ destination }}: {{ type_string }} = UNSET
-if not isinstance({{ source }}, Unset):
-    {{ destination }} = {{ transformed }}
-{%- endif %}
+field_list.append(({{ destination }}, {{ transformed }}))
 {% endmacro %}
diff --git a/openapi_python_client/templates/property_templates/union_property.py.jinja b/openapi_python_client/templates/property_templates/union_property.py.jinja
index dbf7ee9dc..5f76702f9 100644
--- a/openapi_python_client/templates/property_templates/union_property.py.jinja
+++ b/openapi_python_client/templates/property_templates/union_property.py.jinja
@@ -75,25 +75,28 @@ else:
 {% endmacro %}
 
 
-{% macro transform_multipart(property, source, destination) %}
-{% set ns = namespace(has_if = false) %}
-{{ destination }}: {{ property.get_type_string(json=False, multipart=True) }}
-
-{% if not property.required %}
-if isinstance({{ source }}, Unset):
-    {{ destination }} = UNSET
-    {% set ns.has_if = true %}
+{% macro instance_check(inner_property, source) %}
+{% if inner_property.get_instance_type_string() == "None" %}
+if {{ source }} is None:
+{% else %}
+if isinstance({{ source }}, {{ inner_property.get_instance_type_string() }}):
 {% endif %}
+{% endmacro %}
+
+{% macro multipart(property, source, destination) %}
+{% set ns = namespace(has_if = false) %}
 {% for inner_property in property.inner_properties %}
 {% if not ns.has_if %}
-if isinstance({{ source }}, {{ inner_property.get_instance_type_string() }}):
+{{ instance_check(inner_property, source) }}
 {% set ns.has_if = true %}
 {% elif not loop.last %}
-elif isinstance({{ source }}, {{ inner_property.get_instance_type_string() }}):
+
+el{{ instance_check(inner_property, source) }}
 {% else %}
+
 else:
 {% endif %}
 {% import "property_templates/" + inner_property.template as inner_template %}
-    {{ inner_template.transform_multipart(inner_property, source, destination) | indent(4) | trim }}
-{% endfor %}
+    {{ inner_template.multipart(inner_property, source, destination) | indent(4) | trim }}
+{%- endfor -%}
 {% endmacro %}
diff --git a/openapi_python_client/templates/property_templates/uuid_property.py.jinja b/openapi_python_client/templates/property_templates/uuid_property.py.jinja
index 1f91c1e3a..922cf0f89 100644
--- a/openapi_python_client/templates/property_templates/uuid_property.py.jinja
+++ b/openapi_python_client/templates/property_templates/uuid_property.py.jinja
@@ -26,13 +26,6 @@ if not isinstance({{ source }}, Unset):
 {%- endif %}
 {% endmacro %}
 
-{% macro transform_multipart(property, source, destination) %}
-{% if property.required %}
-{{ destination }} = str({{ source }})
-{%- else %}
-{% set type_annotation = property.get_type_string(json=True) | replace("str", "bytes") %}
-{{ destination }}: {{ type_annotation }} = UNSET
-if not isinstance({{ source }}, Unset):
-    {{ destination }} = str({{ source }})
-{%- endif %}
+{% macro multipart(property, source, destination) %}
+field_list.append(({{ destination }},str({{ source }})))
 {% endmacro %}
diff --git a/pyproject.toml b/pyproject.toml
index ac668fd78..c2a704086 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -129,7 +129,7 @@ composite = ["test --cov openapi_python_client tests --cov-report=term-missing"]
 
 [tool.pdm.scripts.regen_integration]
 shell = """
-openapi-python-client generate --overwrite --url https://raw.githubusercontent.com/openapi-generators/openapi-test-server/main/openapi.json --config integration-tests/config.yaml --meta pdm --output-path integration-tests \
+openapi-python-client generate --overwrite --url https://raw.githubusercontent.com/openapi-generators/openapi-test-server/main/openapi.yaml --config integration-tests/config.yaml --meta pdm --output-path integration-tests \
 """
 
 [build-system]