Fix required field default rendering and --use-default nullable types

src/datamodel_code_generator/model/base.py

@@ -173,6 +173,7 @@ class DataModelFieldBase(_BaseModel):
     use_frozen_field: bool = False
     use_serialization_alias: bool = False
     use_default_factory_for_optional_nested_models: bool = False
+    use_default_with_required: bool = False
 
     if not TYPE_CHECKING:  # pragma: no branch
 

src/datamodel_code_generator/model/dataclass.py

@@ -39,7 +39,8 @@
 def has_field_assignment(field: DataModelFieldBase) -> bool:
     """Check if a dataclass field has a default value or field() assignment."""
     return bool(field.field) or not (
-        field.required or (field.represented_default == "None" and field.strip_default_none)
+        (field.required and not field.use_default_with_required)
+        or (field.represented_default == "None" and field.strip_default_none)
     )
 
 
@@ -172,7 +173,7 @@ def __str__(self) -> str:
         if self.default != UNDEFINED and self.default is not None:
             data["default"] = self.default
 
-        if self.required:
+        if self.required and not self.use_default_with_required:
             data = {
                 k: v
                 for k, v in data.items()

src/datamodel_code_generator/model/msgspec.py

@@ -70,7 +70,11 @@ def __str__(self) -> str:
 
 
 def _has_field_assignment(field: DataModelFieldBase) -> bool:
-    return not (field.required or (field.represented_default == "None" and field.strip_default_none))
+    return (
+        bool(field.field)
+        or field.use_default_with_required
+        or not (field.required or (field.represented_default == "None" and field.strip_default_none))
+    )
 
 
 DataModelFieldBaseT = TypeVar("DataModelFieldBaseT", bound=DataModelFieldBase)
@@ -311,7 +315,7 @@ def __str__(self) -> str:  # noqa: PLR0912
         elif self._not_required and "default_factory" not in data:
             data["default"] = None if self.nullable else UNSET
 
-        if self.required:
+        if self.required and not self.use_default_with_required:
             data = {
                 k: v
                 for k, v in data.items()

src/datamodel_code_generator/model/pydantic_base.py

@@ -202,7 +202,7 @@ def __str__(self) -> str:  # noqa: PLR0912
         field_arguments = sorted(f"{k}={v!r}" for k, v in data.items() if v is not None)
 
         if not field_arguments and not default_factory:
-            if self.nullable and self.required:
+            if self.nullable and self.required and not self.use_default_with_required:
                 return "Field(...)"  # Field() is for mypy
             return ""
 
@@ -211,7 +211,12 @@ def __str__(self) -> str:  # noqa: PLR0912
 
         if self.use_annotated:
             field_arguments = self._process_annotated_field_arguments(field_arguments)
-        elif self.required and not default_factory and not self.extras.get("validate_default"):
+        elif (
+            self.required
+            and not self.use_default_with_required
+            and not default_factory
+            and not self.extras.get("validate_default")
+        ):
             field_arguments = ["...", *field_arguments]
         elif not default_factory:
             default_repr = repr_set_sorted(self.default) if isinstance(self.default, set) else repr(self.default)

src/datamodel_code_generator/model/template/dataclass.jinja2

@@ -30,7 +30,7 @@ class {{ class_name }}:
     {{ field.name }}: {{ field.type_hint }} = {{ field.field }}
     {%- else %}
     {{ field.name }}: {{ field.type_hint }}
-    {%- if not (field.required or (field.represented_default == 'None' and field.strip_default_none))
+    {%- if not ((field.required and not field.use_default_with_required) or (field.represented_default == 'None' and field.strip_default_none))
             %} = {{ field.represented_default }}
     {%- endif -%}
     {%- endif %}

src/datamodel_code_generator/model/template/msgspec.jinja2

@@ -29,7 +29,7 @@ class {{ class_name }}:
     {%- else %}
     {{ field.name }}: {{ field.type_hint }}
     {%- endif %}
-    {%- if not field.field and (not field.required or field.data_type.is_optional or field.nullable)
+    {%- if not field.field and (not field.required or field.use_default_with_required or field.data_type.is_optional or field.nullable)
             %} = {{ field.represented_default }}
     {%- endif -%}
     {%- endif %}

src/datamodel_code_generator/model/template/pydantic_v2/BaseModel.jinja2

@@ -27,7 +27,7 @@ class {{ class_name }}({{ base_class }}):{% if comment is defined %}  # {{ comme
     {%- else %}
     {{ field.name }}: {{ field.type_hint }}
     {%- endif %}
-    {%- if not field.has_default_factory_in_field and not field.required and (field.represented_default != 'None' or not field.strip_default_none or field.data_type.is_optional)
+    {%- if not field.has_default_factory_in_field and (not field.required or field.use_default_with_required) and (field.represented_default != 'None' or not field.strip_default_none or field.data_type.is_optional)
             %} = {{ field.represented_default }}
     {%- endif -%}
     {%- endif %}

src/datamodel_code_generator/model/template/pydantic_v2/dataclass.jinja2

@@ -41,7 +41,7 @@ class {{ class_name }}:
     {%- else %}
     {{ field.name }}: {{ field.type_hint }}
     {%- endif %}
-    {%- if not field.has_default_factory_in_field and not field.required and (field.represented_default != 'None' or not field.strip_default_none or field.data_type.is_optional)
+    {%- if not field.has_default_factory_in_field and (not field.required or field.use_default_with_required) and (field.represented_default != 'None' or not field.strip_default_none or field.data_type.is_optional)
             %} = {{ field.represented_default }}
     {%- endif -%}
     {%- endif %}

src/datamodel_code_generator/parser/base.py

@@ -2180,6 +2180,8 @@ def __set_validate_default_on_fields(  # noqa: PLR6301
             if isinstance(model, Enum):
                 continue
             for model_field in model.fields:
+                if model_field.required and not model_field.use_default_with_required:
+                    continue
                 if model_field.default is None or model_field.default is UNDEFINED:
                     continue
                 if isinstance(model_field.default, Member):
@@ -2227,6 +2229,8 @@ def __override_required_field(
                 copied_original_field.data_type = data_type
                 copied_original_field.parent = model
                 copied_original_field.required = True
+                if self.apply_default_values_for_required_fields and copied_original_field.has_default:
+                    copied_original_field.use_default_with_required = True
                 model.fields.insert(index, copied_original_field)
                 model.fields.remove(model_field)
 

src/datamodel_code_generator/parser/graphql.py

@@ -372,8 +372,7 @@ def parse_field(
             class_name=class_name,
         )
 
-        if self.apply_default_values_for_required_fields and effective_has_default:
-            required = False
+        use_default_with_required = required and self.apply_default_values_for_required_fields and effective_has_default
 
         extras = {} if self.default_field_extras is None else self.default_field_extras.copy()
 
@@ -405,6 +404,7 @@ def parse_field(
             original_name=field_name,
             has_default=effective_has_default,
             use_serialization_alias=self.use_serialization_alias,
+            use_default_with_required=use_default_with_required,
         )
 
     def parse_object_like(

src/datamodel_code_generator/parser/jsonschema.py

@@ -1202,6 +1202,7 @@ def get_object_field(  # noqa: PLR0913
         original_field_name: str | None,
         effective_default: Any = None,
         effective_has_default: bool | None = None,
+        use_default_with_required: bool = False,
     ) -> DataModelFieldBase:
         """Create a data model field from a JSON Schema object field."""
         default_value = effective_default if effective_has_default is not None else field.default
@@ -1252,6 +1253,7 @@ def get_object_field(  # noqa: PLR0913
             use_frozen_field=self.use_frozen_field,
             use_serialization_alias=self.use_serialization_alias,
             use_default_factory_for_optional_nested_models=self.use_default_factory_for_optional_nested_models,
+            use_default_with_required=use_default_with_required,
         )
 
     def get_data_type(self, obj: JsonSchemaObject) -> DataType:
@@ -2478,22 +2480,22 @@ def _parse_object_common_part(  # noqa: PLR0912, PLR0913, PLR0915
                 return self.data_type(reference=base_classes[0])
         if required:
             for field in fields:
-                if self.force_optional_for_required_fields or (  # pragma: no cover
-                    self.apply_default_values_for_required_fields and field.has_default
-                ):
+                if self.force_optional_for_required_fields:  # pragma: no cover
                     continue  # pragma: no cover
                 if (field.original_name or field.name) in required:
                     field.required = True
+                    if self.apply_default_values_for_required_fields and field.has_default:
+                        field.use_default_with_required = True
         if obj.required:
             field_name_to_field = {f.original_name or f.name: f for f in fields}
             for required_ in obj.required:
                 if required_ in field_name_to_field:
                     field = field_name_to_field[required_]
-                    if self.force_optional_for_required_fields or (
-                        self.apply_default_values_for_required_fields and field.has_default
-                    ):
+                    if self.force_optional_for_required_fields:
                         continue
                     field.required = True
+                    if self.apply_default_values_for_required_fields and field.has_default:
+                        field.use_default_with_required = True
                 else:
                     fields.append(
                         self.data_model_field_type(required=True, original_name=required_, data_type=DataType())
@@ -2829,12 +2831,13 @@ def parse_object_fields(
                 class_name=class_name,
             )
 
-            if self.force_optional_for_required_fields or (
-                self.apply_default_values_for_required_fields and effective_has_default
-            ):
+            if self.force_optional_for_required_fields:
                 required: bool = False
             else:
                 required = original_field_name in requires
+            use_default_with_required = (
+                required and self.apply_default_values_for_required_fields and effective_has_default
+            )
             fields.append(
                 self.get_object_field(
                     field_name=field_name,
@@ -2845,6 +2848,7 @@ def parse_object_fields(
                     original_field_name=original_field_name,
                     effective_default=effective_default,
                     effective_has_default=effective_has_default,
+                    use_default_with_required=use_default_with_required,
                 )
             )
         return fields

src/datamodel_code_generator/parser/openapi.py

@@ -508,7 +508,7 @@ def _get_model_name(cls, path_name: str, method: str, suffix: str) -> str:
         camel_path_name = snake_to_upper_camel(normalized)
         return f"{camel_path_name}{method.capitalize()}{suffix}"
 
-    def parse_all_parameters(  # noqa: PLR0912, PLR0914, PLR0915
+    def parse_all_parameters(  # noqa: PLR0912, PLR0914
         self,
         name: str,
         parameters: list[ReferenceObject | ParameterObject],
@@ -551,8 +551,9 @@ def parse_all_parameters(  # noqa: PLR0912, PLR0914, PLR0915
                     class_name=reference.name,
                 )
                 effective_required = parameter.required
-                if self.apply_default_values_for_required_fields and effective_has_default:
-                    effective_required = False
+                use_default_with_required = (
+                    effective_required and self.apply_default_values_for_required_fields and effective_has_default
+                )
                 fields.append(
                     self.get_object_field(
                         field_name=field_name,
@@ -563,6 +564,7 @@ def parse_all_parameters(  # noqa: PLR0912, PLR0914, PLR0915
                         alias=alias,
                         effective_default=effective_default,
                         effective_has_default=effective_has_default,
+                        use_default_with_required=use_default_with_required,
                     )
                 )
             else:
@@ -600,8 +602,9 @@ def parse_all_parameters(  # noqa: PLR0912, PLR0914, PLR0915
                     class_name=reference.name,
                 )
                 effective_required = parameter.required
-                if self.apply_default_values_for_required_fields and effective_has_default:
-                    effective_required = False
+                use_default_with_required = (
+                    effective_required and self.apply_default_values_for_required_fields and effective_has_default
+                )
                 # Handle multiple aliases (Pydantic v2 AliasChoices)
                 single_alias: str | None = None
                 validation_aliases: list[str] | None = None
@@ -639,6 +642,7 @@ def parse_all_parameters(  # noqa: PLR0912, PLR0914, PLR0915
                         has_default=effective_has_default,
                         type_has_null=object_schema.type_has_null if object_schema else None,
                         use_serialization_alias=self.use_serialization_alias,
+                        use_default_with_required=use_default_with_required,
                     )
                 )
 

tests/data/expected/main/graphql/default_values_required_use_default.py

@@ -29,6 +29,6 @@
 
 class User(BaseModel):
     id: ID
-    name: String | None = 'default_user'
-    status: String | None = 'active'
+    name: String = 'default_user'
+    status: String = 'active'
     typename__: Literal['User'] | None = Field('User', alias='__typename')

tests/data/expected/main/graphql/pydantic_v2_empty_list_default.py

@@ -26,8 +26,8 @@ class Container(BaseModel):
 
 
 class PodSpec(BaseModel):
-    container_list: list[Container] = Field([], validate_default=True)
-    container_list_or_none: list[Container | None] = Field([], validate_default=True)
+    container_list: list[Container]
+    container_list_or_none: list[Container | None]
     container_or_none_list_or_none: list[Container | None] | None = Field(
         [], validate_default=True
     )

tests/data/expected/main/jsonschema/all_of_use_default.py

@@ -8,5 +8,5 @@
 
 
 class Item(BaseModel):
-    test: str | None = 'test123'
-    testarray: list[str] | None = Field(['test123'], min_length=1, title='test array')
+    test: str = 'test123'
+    testarray: list[str] = Field(['test123'], min_length=1, title='test array')

tests/data/expected/main/jsonschema/allof_inherited_required_use_default.py

@@ -0,0 +1,15 @@
+# generated by datamodel-codegen:
+#   filename:  allof_inherited_required_use_default.json
+#   timestamp: 2019-07-26T00:00:00+00:00
+
+from __future__ import annotations
+
+from pydantic import BaseModel
+
+
+class Base(BaseModel):
+    id: int | None = 1
+
+
+class Container(Base):
+    id: int = 1

tests/data/expected/main/jsonschema/allof_required_use_default.py

@@ -0,0 +1,16 @@
+# generated by datamodel-codegen:
+#   filename:  allof_required_use_default.json
+#   timestamp: 2019-07-26T00:00:00+00:00
+
+from __future__ import annotations
+
+from pydantic import BaseModel
+
+
+class Base(BaseModel):
+    id: int
+
+
+class Container(Base):
+    name: str = 'unnamed'
+    tag: str

tests/data/expected/main/jsonschema/force_optional_required.py

@@ -0,0 +1,16 @@
+# generated by datamodel-codegen:
+#   filename:  force_optional_required.json
+#   timestamp: 2019-07-26T00:00:00+00:00
+
+from __future__ import annotations
+
+from pydantic import BaseModel
+
+
+class Base(BaseModel):
+    id: int | None = None
+
+
+class Container(Base):
+    name: str | None = None
+    value: int | None = None

tests/data/expected/main/jsonschema/use_default_msgspec_field_ordering.py

@@ -0,0 +1,16 @@
+# generated by datamodel-codegen:
+#   filename:  allof_required_use_default.json
+#   timestamp: 2019-07-26T00:00:00+00:00
+
+from __future__ import annotations
+
+from msgspec import Struct
+
+
+class Base(Struct):
+    id: int
+
+
+class Container(Base):
+    tag: str
+    name: str = 'unnamed'

tests/data/expected/main/jsonschema/use_default_required_null_default.py

@@ -0,0 +1,13 @@
+# generated by datamodel-codegen:
+#   filename:  use_default_required_null_default.json
+#   timestamp: 2019-07-26T00:00:00+00:00
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+
+
+@dataclass
+class Container:
+    b: int
+    a: str | None = None

tests/data/expected/main/jsonschema/use_default_strict_nullable_required.py

@@ -0,0 +1,11 @@
+# generated by datamodel-codegen:
+#   filename:  use_default_strict_nullable_required.json
+#   timestamp: 2019-07-26T00:00:00+00:00
+
+from __future__ import annotations
+
+from pydantic import BaseModel
+
+
+class Container(BaseModel):
+    x: str | None = 'hello'

tests/data/expected/main/openapi/default_values_parameters_use_default.py

@@ -12,8 +12,8 @@ class Filter(BaseModel):
 
 
 class UsersGetParametersQuery(BaseModel):
-    status: str | None = 'active'
-    filter: Filter | None = Field({}, validate_default=True)
+    status: str = 'active'
+    filter: Filter = Field({}, validate_default=True)
 
 
 class User(BaseModel):