Add support for setting strict_nullable from CLI

README.md

@@ -60,6 +60,8 @@ Options:
   --specify-tags TEXT
   -c, --custom-visitor PATH
   --disable-timestamp
+  --strict-nullable               Respect explicit OpenAPI nullable flags when
+                                  generating models.
   --include-request-argument      Auto-inject a FastAPI Request parameter into
                                   operations when not present.
   -d, --output-model-type [pydantic_v2.BaseModel|pydantic_v2.dataclass|dataclasses.dataclass|typing.TypedDict|msgspec.Struct]

docs/cli-reference.md

@@ -18,6 +18,8 @@ Options:
   --specify-tags TEXT
   -c, --custom-visitor PATH
   --disable-timestamp
+  --strict-nullable               Respect explicit OpenAPI nullable flags when
+                                  generating models.
   --include-request-argument      Auto-inject a FastAPI Request parameter into
                                   operations when not present.
   -d, --output-model-type [pydantic_v2.BaseModel|pydantic_v2.dataclass|dataclasses.dataclass|typing.TypedDict|msgspec.Struct]
@@ -99,6 +101,14 @@ Omit the generated timestamp header from output files.
 
 Input schema: `openapi/disable_timestamp/simple.yaml`
 
+### --strict-nullable
+
+Respect explicit OpenAPI nullable flags when generating models.
+
+`fastapi-codegen --input openapi/default_template/nullable_test.yaml --output app --strict-nullable`
+
+Input schema: `openapi/default_template/nullable_test.yaml`
+
 ### --generate-routers
 
 Generate modular router files from tagged OpenAPI operations.

docs/index.md

@@ -57,6 +57,8 @@ Options:
   --specify-tags TEXT
   -c, --custom-visitor PATH
   --disable-timestamp
+  --strict-nullable               Respect explicit OpenAPI nullable flags when
+                                  generating models.
   --include-request-argument      Auto-inject a FastAPI Request parameter into
                                   operations when not present.
   -d, --output-model-type [pydantic_v2.BaseModel|pydantic_v2.dataclass|dataclasses.dataclass|typing.TypedDict|msgspec.Struct]

docs/llms-full.txt

@@ -59,6 +59,8 @@ Options:
   --specify-tags TEXT
   -c, --custom-visitor PATH
   --disable-timestamp
+  --strict-nullable               Respect explicit OpenAPI nullable flags when
+                                  generating models.
   --include-request-argument      Auto-inject a FastAPI Request parameter into
                                   operations when not present.
   -d, --output-model-type [pydantic_v2.BaseModel|pydantic_v2.dataclass|dataclasses.dataclass|typing.TypedDict|msgspec.Struct]
@@ -342,6 +344,8 @@ Options:
   --specify-tags TEXT
   -c, --custom-visitor PATH
   --disable-timestamp
+  --strict-nullable               Respect explicit OpenAPI nullable flags when
+                                  generating models.
   --include-request-argument      Auto-inject a FastAPI Request parameter into
                                   operations when not present.
   -d, --output-model-type [pydantic_v2.BaseModel|pydantic_v2.dataclass|dataclasses.dataclass|typing.TypedDict|msgspec.Struct]
@@ -423,6 +427,14 @@ Omit the generated timestamp header from output files.
 
 Input schema: `openapi/disable_timestamp/simple.yaml`
 
+### --strict-nullable
+
+Respect explicit OpenAPI nullable flags when generating models.
+
+`fastapi-codegen --input openapi/default_template/nullable_test.yaml --output app --strict-nullable`
+
+Input schema: `openapi/default_template/nullable_test.yaml`
+
 ### --generate-routers
 
 Generate modular router files from tagged OpenAPI operations.
@@ -515,15 +527,15 @@ Run `tox run -e schema-docs` after changing supported inputs or model backends.
 
 | Format | Status | Evidence | Notes |
 |--------|--------|----------|-------|
-| OpenAPI YAML | tested | `tests/data/openapi/**/*.yaml` (23 fixtures) | Primary fixture format exercised under `tests/data/openapi/**/*.yaml`. |
+| OpenAPI YAML | tested | `tests/data/openapi/**/*.yaml` (24 fixtures) | Primary fixture format exercised under `tests/data/openapi/**/*.yaml`. |
 | OpenAPI JSON | tested | `tests/main/test_main.py::test_generate_from_json_input` | Covered by the JSON conversion CLI test in `tests/main/test_main.py`. |
 | Remote HTTP `$ref` targets | tested | `tests/main/test_main.py::test_generate_remote_ref` | Covered by the remote `$ref` generation test against a live HTTP server. |
 
 ## Fixture Suites
 
 | Suite | Fixtures | Example files | Notes |
 |-------|----------|---------------|-------|
-| Default template | 16 | `body_and_parameters.yaml`, `content_in_parameters.yaml`, `content_in_parameters_inline.yaml` | Core single-file generation scenarios exercised by the main CLI tests. |
+| Default template | 17 | `body_and_parameters.yaml`, `content_in_parameters.yaml`, `content_in_parameters_inline.yaml` | Core single-file generation scenarios exercised by the main CLI tests. |
 | Coverage fixtures | 3 | `callbacks.yaml`, `callbacks_with_operation_id.yaml`, `non_200_responses.yaml` | Focused fixtures for callbacks, non-200 responses, and other regression edges. |
 | Custom template overrides | 1 | `custom_security.yaml` | Template override coverage for `--template-dir`. |
 | Timestamp suppression | 1 | `simple.yaml` | Fixtures that exercise `--disable-timestamp`. |

docs/supported_formats.md

@@ -7,15 +7,15 @@ Run `tox run -e schema-docs` after changing supported inputs or model backends.
 
 | Format | Status | Evidence | Notes |
 |--------|--------|----------|-------|
-| OpenAPI YAML | tested | `tests/data/openapi/**/*.yaml` (23 fixtures) | Primary fixture format exercised under `tests/data/openapi/**/*.yaml`. |
+| OpenAPI YAML | tested | `tests/data/openapi/**/*.yaml` (24 fixtures) | Primary fixture format exercised under `tests/data/openapi/**/*.yaml`. |
 | OpenAPI JSON | tested | `tests/main/test_main.py::test_generate_from_json_input` | Covered by the JSON conversion CLI test in `tests/main/test_main.py`. |
 | Remote HTTP `$ref` targets | tested | `tests/main/test_main.py::test_generate_remote_ref` | Covered by the remote `$ref` generation test against a live HTTP server. |
 
 ## Fixture Suites
 
 | Suite | Fixtures | Example files | Notes |
 |-------|----------|---------------|-------|
-| Default template | 16 | `body_and_parameters.yaml`, `content_in_parameters.yaml`, `content_in_parameters_inline.yaml` | Core single-file generation scenarios exercised by the main CLI tests. |
+| Default template | 17 | `body_and_parameters.yaml`, `content_in_parameters.yaml`, `content_in_parameters_inline.yaml` | Core single-file generation scenarios exercised by the main CLI tests. |
 | Coverage fixtures | 3 | `callbacks.yaml`, `callbacks_with_operation_id.yaml`, `non_200_responses.yaml` | Focused fixtures for callbacks, non-200 responses, and other regression edges. |
 | Custom template overrides | 1 | `custom_security.yaml` | Template override coverage for `--template-dir`. |
 | Timestamp suppression | 1 | `simple.yaml` | Fixtures that exercise `--disable-timestamp`. |

fastapi_code_generator/_types/generate_config_dict.py

@@ -30,5 +30,6 @@ class GenerateConfigDict(TypedDict):
     ]
     python_version: NotRequired[Literal['3.10', '3.11', '3.12', '3.13', '3.14']]
     specify_tags: NotRequired[str | None]
+    strict_nullable: NotRequired[bool]
     template_dir: NotRequired[str | None]
     use_annotated: NotRequired[bool]

fastapi_code_generator/cli.py

@@ -90,6 +90,11 @@ def main(
         None, "--custom-visitor", "-c"
     ),
     disable_timestamp: bool = typer.Option(False, "--disable-timestamp"),
+    strict_nullable: bool = typer.Option(
+        False,
+        "--strict-nullable",
+        help="Respect explicit OpenAPI nullable flags when generating models.",
+    ),
     include_request_argument: bool = typer.Option(
         False,
         "--include-request-argument",
@@ -137,6 +142,7 @@ def main(
         enum_field_as_literal=enum_field_as_literal or None,
         custom_visitors=custom_visitors,
         disable_timestamp=disable_timestamp,
+        strict_nullable=strict_nullable,
         include_request_argument=include_request_argument,
         generate_routers=generate_routers,
         specify_tags=specify_tags,
@@ -176,6 +182,7 @@ def generate_code(
     enum_field_as_literal: Optional[LiteralType] = None,
     custom_visitors: Optional[List[Path]] = None,
     disable_timestamp: bool = False,
+    strict_nullable: bool = False,
     include_request_argument: bool = False,
     generate_routers: Optional[bool] = None,
     specify_tags: Optional[str] = None,
@@ -209,6 +216,7 @@ def generate_code(
         dump_resolve_reference_action=data_model_types.dump_resolve_reference_action,
         custom_template_dir=model_template_dir,
         target_python_version=python_version,
+        strict_nullable=strict_nullable,
         include_request_argument=include_request_argument,
         use_annotated=use_annotated,
     )

fastapi_code_generator/config.py

@@ -150,6 +150,11 @@ class GenerateConfig(BaseModel):
         description="Omit timestamp headers from generated files.",
         json_schema_extra=cast(Any, _cli_metadata("--disable-timestamp")),
     )
+    strict_nullable: bool = Field(
+        default=False,
+        description="Respect explicit OpenAPI nullable flags when generating models.",
+        json_schema_extra=cast(Any, _cli_metadata("--strict-nullable")),
+    )
     include_request_argument: bool = Field(
         default=False,
         description=(

fastapi_code_generator/prompt_data.py

@@ -121,6 +121,17 @@
             'type': 'boolean',
             'choices': [],
         },
+        {
+            'name': 'strict_nullable',
+            'cli_flags': ['--strict-nullable'],
+            'description': 'Respect explicit OpenAPI nullable flags when '
+            'generating models.',
+            'required': False,
+            'default': False,
+            'multiple': False,
+            'type': 'boolean',
+            'choices': [],
+        },
         {
             'name': 'include_request_argument',
             'cli_flags': ['--include-request-argument'],
@@ -261,6 +272,19 @@
             ],
             'input_schema': 'openapi/disable_timestamp/simple.yaml',
         },
+        {
+            'options': ['--strict-nullable'],
+            'description': 'Respect explicit OpenAPI nullable flags when '
+            'generating models.',
+            'cli_args': [
+                '--input',
+                'openapi/default_template/nullable_test.yaml',
+                '--output',
+                'app',
+                '--strict-nullable',
+            ],
+            'input_schema': 'openapi/default_template/nullable_test.yaml',
+        },
         {
             'options': ['--generate-routers'],
             'description': 'Generate modular router files from tagged OpenAPI '
@@ -461,7 +485,7 @@
     '\n'
     '| Format | Status | Evidence | Notes |\n'
     '|--------|--------|----------|-------|\n'
-    '| OpenAPI YAML | tested | `tests/data/openapi/**/*.yaml` (23 '
+    '| OpenAPI YAML | tested | `tests/data/openapi/**/*.yaml` (24 '
     'fixtures) | Primary fixture format exercised under '
     '`tests/data/openapi/**/*.yaml`. |\n'
     '| OpenAPI JSON | tested | '
@@ -477,7 +501,7 @@
     '\n'
     '| Suite | Fixtures | Example files | Notes |\n'
     '|-------|----------|---------------|-------|\n'
-    '| Default template | 16 | `body_and_parameters.yaml`, '
+    '| Default template | 17 | `body_and_parameters.yaml`, '
     '`content_in_parameters.yaml`, '
     '`content_in_parameters_inline.yaml` | Core single-file '
     'generation scenarios exercised by the main CLI tests. |\n'

tests/data/expected/openapi/default_template/nullable_test/main.py

@@ -0,0 +1,24 @@
+# generated by fastapi-codegen:
+#   filename:  nullable_test.yaml
+#   timestamp: 2020-06-19T00:00:00+00:00
+
+from __future__ import annotations
+
+from fastapi import FastAPI
+
+from .models import User
+
+app = FastAPI(
+    version='1.0.0',
+    title='Nullable Test API',
+    description='API for testing nullable field behavior',
+    servers=[{'url': 'http://api.example.com/v1'}],
+)
+
+
+@app.get('/users', response_model=User)
+def get_user_details() -> User:
+    """
+    Get user details
+    """
+    pass

tests/data/expected/openapi/default_template/nullable_test/models.py

@@ -0,0 +1,21 @@
+# generated by fastapi-codegen:
+#   filename:  nullable_test.yaml
+#   timestamp: 2020-06-19T00:00:00+00:00
+
+from __future__ import annotations
+
+from typing import Optional
+
+from pydantic import BaseModel, Field
+
+
+class User(BaseModel):
+    id: int
+    username: str
+    email: Optional[str] = Field(
+        None, description="User's email address (explicitly nullable)"
+    )
+    phone: str = Field(..., description="User's phone number (explicitly non-nullable)")
+    nickname: Optional[str] = Field(
+        None, description="User's nickname (optional, not nullable under strict mode)"
+    )

tests/data/expected/openapi/default_template/nullable_test_strict/main.py

@@ -0,0 +1,24 @@
+# generated by fastapi-codegen:
+#   filename:  nullable_test.yaml
+#   timestamp: 2020-06-19T00:00:00+00:00
+
+from __future__ import annotations
+
+from fastapi import FastAPI
+
+from .models import User
+
+app = FastAPI(
+    version='1.0.0',
+    title='Nullable Test API',
+    description='API for testing nullable field behavior',
+    servers=[{'url': 'http://api.example.com/v1'}],
+)
+
+
+@app.get('/users', response_model=User)
+def get_user_details() -> User:
+    """
+    Get user details
+    """
+    pass

tests/data/expected/openapi/default_template/nullable_test_strict/models.py

@@ -0,0 +1,21 @@
+# generated by fastapi-codegen:
+#   filename:  nullable_test.yaml
+#   timestamp: 2020-06-19T00:00:00+00:00
+
+from __future__ import annotations
+
+from typing import Optional
+
+from pydantic import BaseModel, Field
+
+
+class User(BaseModel):
+    id: int
+    username: str
+    email: Optional[str] = Field(
+        None, description="User's email address (explicitly nullable)"
+    )
+    phone: str = Field(..., description="User's phone number (explicitly non-nullable)")
+    nickname: Optional[str] = Field(
+        None, description="User's nickname (optional, not nullable under strict mode)"
+    )

tests/data/openapi/default_template/nullable_test.yaml

@@ -0,0 +1,44 @@
+openapi: "3.0.0"
+info:
+  version: 1.0.0
+  title: Nullable Test API
+  description: API for testing nullable field behavior
+servers:
+  - url: http://api.example.com/v1
+paths:
+  /users:
+    get:
+      summary: Get user details
+      operationId: getUserDetails
+      responses:
+        "200":
+          description: User details
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/User"
+components:
+  schemas:
+    User:
+      type: object
+      required:
+        - id
+        - phone
+        - username
+      properties:
+        id:
+          type: integer
+          format: int64
+        username:
+          type: string
+        email:
+          type: string
+          nullable: true
+          description: User's email address (explicitly nullable)
+        phone:
+          type: string
+          nullable: false
+          description: User's phone number (explicitly non-nullable)
+        nickname:
+          type: string
+          description: User's nickname (optional, not nullable under strict mode)

tests/main/test_main.py

@@ -431,6 +431,33 @@ def test_disable_timestamp(oas_file: Path, output_dir: Path) -> None:
     )
 
 
+@pytest.mark.cli_doc(
+    options=["--strict-nullable"],
+    option_description="Respect explicit OpenAPI nullable flags when generating models.",
+    cli_args=[
+        "--input",
+        "openapi/default_template/nullable_test.yaml",
+        "--output",
+        "app",
+        "--strict-nullable",
+    ],
+    input_schema="openapi/default_template/nullable_test.yaml",
+    golden_output="openapi/default_template/nullable_test_strict/models.py",
+)
+@freeze_time("2020-06-19")
+def test_generate_with_strict_nullable(output_dir: Path) -> None:
+    run_cli_and_assert(
+        input_path=DATA_PATH
+        / OPEN_API_DEFAULT_TEMPLATE_DIR_NAME
+        / "nullable_test.yaml",
+        output_path=output_dir,
+        expected_path=EXPECTED_OPENAPI_PATH
+        / "default_template"
+        / "nullable_test_strict",
+        extra_args=["--strict-nullable"],
+    )
+
+
 @pytest.mark.cli_doc(
     options=["--generate-routers"],
     option_description="Generate modular router files from tagged OpenAPI operations.",