Fix required list fields ignoring empty default values (#2958)

* Fix required list fields ignoring empty default values

* Add parameterized test for pydantic v1/v2 default value handling

* Fix incorrect default value in test schema for FamilyPets

Author: koxudaxi

src/datamodel_code_generator/model/pydantic/base_model.py

@@ -220,7 +220,7 @@ def __str__(self) -> str:  # noqa: PLR0912
             elif isinstance(discriminator, dict):  # pragma: no cover
                 data["discriminator"] = discriminator["propertyName"]
 
-        if self.required:
+        if self.required and not self.has_default:
             default_factory = None
         elif self.default is not UNDEFINED and self.default is not None and "default_factory" not in data:
             default_factory = self._get_default_as_pydantic_model()
@@ -249,7 +249,7 @@ def __str__(self) -> str:  # noqa: PLR0912
 
         if self.use_annotated:
             field_arguments = self._process_annotated_field_arguments(field_arguments)
-        elif self.required:
+        elif self.required and not default_factory:
             field_arguments = ["...", *field_arguments]
         elif not default_factory:
             default_repr = repr_set_sorted(self.default) if isinstance(self.default, set) else repr(self.default)

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

@@ -25,11 +25,17 @@ class Pet(BaseModel):
 
 
 class Family(BaseModel):
-    __root__: list[ID] = ['abc', 'efg']
+    __root__: list[ID] = Field(
+        default_factory=lambda: [ID.parse_obj(v) for v in ['abc', 'efg']]
+    )
 
 
 class FamilyPets(BaseModel):
-    __root__: list[Pet] = ['taro', 'shiro']
+    __root__: list[Pet] = Field(
+        default_factory=lambda: [
+            Pet.parse_obj(v) for v in [{'name': 'taro'}, {'name': 'shiro'}]
+        ]
+    )
 
 
 class Person(BaseModel):

tests/data/expected/main/jsonschema/has_default_value_pydantic_v2.py

@@ -0,0 +1,48 @@
+# generated by datamodel-codegen:
+#   filename:  has_default_value.json
+#   timestamp: 2019-07-26T00:00:00+00:00
+
+from __future__ import annotations
+
+from enum import Enum
+
+from pydantic import BaseModel, Field, RootModel
+
+
+class TeamType(Enum):
+    Department = 'Department'
+    Division = 'Division'
+    BusinessUnit = 'BusinessUnit'
+    Organization = 'Organization'
+
+
+class ID(RootModel[str]):
+    root: str = 'abc'
+
+
+class Pet(BaseModel):
+    name: str | None = None
+
+
+class Family(RootModel[list[ID]]):
+    root: list[ID] = Field(
+        default_factory=lambda: [ID.model_validate(v) for v in ['abc', 'efg']]
+    )
+
+
+class FamilyPets(RootModel[list[Pet]]):
+    root: list[Pet] = Field(
+        default_factory=lambda: [
+            Pet.model_validate(v) for v in [{'name': 'taro'}, {'name': 'shiro'}]
+        ]
+    )
+
+
+class Person(BaseModel):
+    id: ID | None = Field(default_factory=lambda: ID('abc'))
+    user: Pet | None = None
+    firstName: str | None = Field(None, description="The person's first name.")
+    team: TeamType | None = 'Department'
+    anotherTeam: TeamType | None = 'Department'
+    Family_1: Family | None = Field(None, alias='Family')
+    FamilyPets_1: FamilyPets | None = Field(None, alias='FamilyPets')

tests/data/jsonschema/has_default_value.json

@@ -45,8 +45,8 @@
         "$ref": "#/definitions/Pet"
       },
       "default": [
-        "taro",
-        "shiro"
+        {"name": "taro"},
+        {"name": "shiro"}
       ]
     }
   },

tests/main/jsonschema/test_main_jsonschema.py

@@ -3254,14 +3254,26 @@ def test_jsonschema_use_title_as_name_nested_titles_pydantic(output_file: Path)
     )
 
 
-def test_main_jsonschema_has_default_value(output_file: Path) -> None:
+@pytest.mark.parametrize(
+    ("output_model", "expected_file"),
+    [
+        ("pydantic.BaseModel", "has_default_value.py"),
+        pytest.param(
+            "pydantic_v2.BaseModel",
+            "has_default_value_pydantic_v2.py",
+            marks=PYDANTIC_V2_SKIP,
+        ),
+    ],
+)
+def test_main_jsonschema_has_default_value(output_model: str, expected_file: str, output_file: Path) -> None:
     """Test default value handling."""
     run_main_and_assert(
         input_path=JSON_SCHEMA_DATA_PATH / "has_default_value.json",
         output_path=output_file,
         input_file_type="jsonschema",
         assert_func=assert_file_content,
-        expected_file="has_default_value.py",
+        expected_file=expected_file,
+        extra_args=["--output-model-type", output_model],
     )