```JSON
{
    "name": "Foo",
    "description": "An optional description",
    "price": 45.2,
    "tax": 3.5
}
```

Da `description` und `tax` optional sind (mit `None` als Defaultwert), wäre folgendes JSON „`object`“ auch gültig:

```JSON
{
    "name": "Foo",
    "price": 45.2
}
```

与声明查询参数一样，包含默认值的模型属性是可选的，否则就是必选的。默认值为 `None` 的模型属性也是可选的。

例如，上述模型声明如下 JSON **对象**（即 Python **字典**）：

```JSON
{
    "name": "Foo",
    "description": "An optional description",
    "price": 45.2,
    "tax": 3.5
}
```

……由于 `description` 和 `tax` 是可选的（默认值为 `None`），下面的 JSON **对象**也有效：

```JSON
{
    "name": "Foo",
    "price": 45.2
}
```

## 声明请求体参数

from typing import Union

from fastapi import FastAPI, Path
from pydantic import BaseModel

app = FastAPI()


class Item(BaseModel):
    name: str
    description: Union[str, None] = None
    price: float
    tax: Union[float, None] = None


@app.put("/items/{item_id}")
async def update_item(
    *,
    item_id: int = Path(title="The ID of the item to get", ge=0, le=1000),
    q: Union[str, None] = None,

                "get": {
                    "summary": "Read Main",
                    "operationId": "read_main_app_get",
                    "responses": {
                        "200": {
                            "description": "Successful Response",
                            "content": {"application/json": {"schema": {}}},
                        }
                    },
                }
            }
        },

    <artifactId>maven</artifactId>
    <version>4.0.0-alpha-1-SNAPSHOT</version>
  </parent>

  <artifactId>maven-model</artifactId>

  <name>Maven Model</name>
  <description>Model for Maven POM (Project Object Model)</description>

  <dependencies>
    <dependency>
      <groupId>org.apache.maven</groupId>
      <artifactId>maven-api-model</artifactId>
      <version>4.0.0-alpha-1-SNAPSHOT</version>

from typing import Union

from fastapi import FastAPI
from pydantic import BaseModel


class Item(BaseModel):
    name: str
    description: Union[str, None] = None
    price: float
    tax: Union[float, None] = None


app = FastAPI()


@app.put("/items/{item_id}")
async def update_item(item_id: int, item: Item, q: Union[str, None] = None):
    result = {"item_id": item_id, **item.model_dump()}
    if q:

from fastapi import Body, FastAPI
from pydantic import BaseModel

app = FastAPI()


class Item(BaseModel):
    name: str
    description: str | None = None
    price: float
    tax: float | None = None


class User(BaseModel):
    username: str
    full_name: str | None = None


@app.put("/items/{item_id}")
async def update_item(item_id: int, item: Item, user: User, importance: int = Body()):

        // Verify subcommand
        assertEquals(SmbComTransaction.NET_SERVER_ENUM2 & 0xFF, (dst[0] & 0xFF) | ((dst[1] & 0xFF) << 8));

        // Verify description
        byte[] descr = NetServerEnum2.DESCR[0].getBytes("ASCII");
        byte[] writtenDescr = new byte[descr.length];
        System.arraycopy(dst, 2, writtenDescr, 0, descr.length);

from typing import Union

from fastapi import Body, FastAPI
from pydantic import BaseModel

app = FastAPI()


class Item(BaseModel):
    name: str
    description: Union[str, None] = None
    price: float
    tax: Union[float, None] = None


class User(BaseModel):
    username: str
    full_name: Union[str, None] = None


@app.put("/items/{item_id}")
async def update_item(
    *,
    item_id: int,

def test_openapi():
    response = client.get("/openapi.json")
    assert response.status_code == 200, response.text
    openapi_schema = response.json()

    assert openapi_schema["components"]["schemas"]["MyModel"]["description"] == (
        "A model with a form feed character in the title.\n"