# FastAPI 路径参数及校验

### Path 路径参数约束

**注意： 对于必需参数，我们没有顺序要求，有默认值的参数必须放在没有默认值的后面**

```python
from fastapi import FastAPI

app = FastAPI()


# 未约束路径参数内容
@app.get('/a/{name}')
async def name1(name):
    return {'name': name}


# 约束路径参数类型
@app.get('/b/{age}')
async def name(age:int):
    return {'age': age}


# 启动: uvicorn main:app --reload
```

```python
# 未约束
curl 127.0.0.1:8000/a/asdf
{"name":"asdf"}


# 约束错误返回
curl 127.0.0.1:8000/b/asdf
{"detail":[{"loc":["path","age"],"msg":"value is not a valid integer","type":"type_error.integer"}]}


# 约束 int 类型
curl 127.0.0.1:8000/b/1
{"age":1}
```

### 路径参数枚举

```python
class SexyEnum(str, Enum):
    ''' key = value '''
    boy = 1
    girl = 2

@app.get("/sexy/{value}")
async def sexy(value: SexyEnum):
    ''' 通过判断 value 值判断'''
    if value == SexyEnum.boy:
        return {'name': 'boy'}

    if value == SexyEnum.girl:
            return {'name': 'girl'}
```

```python
curl 127.0.0.1:8000/sexy/1
{"name":"boy"}

curl 127.0.0.1:8000/sexy/2
{"name":"girl"}

curl 127.0.0.1:8000/sexy/3
{"detail":[{"loc":["path","value"],"msg":"value is not a valid enumeration member; permitted: '1', '2'","type":"type_error.enum","ctx":{"enum_values":["1","2"]}}]}
```

### 路径参数校验

* 例如传ID， id 必须是 int 类型，并且不能为空，自定义标题为 user id

```python
from typing import Optional, List
from fastapi import FastAPI,Query,Path

app = FastAPI()

@app.get('/items/{id}')
async def items(id: int = Path(..., title='user id')):
    return {'id': id}
```

```python
curl 127.0.0.1:8000/items/1
{"id":1}
```

### \* 号作用

* `*`星号之后所有参数都应称为关键字参数， 必须传入

```python
（键-值对），也称为kwargs 。 即使它们没有默认值。
```

### 路径参数和请求参数结合

```python
from typing import Optional
from fastapi import FastAPI,Query,Path


app = FastAPI()


@app.get('/items/{id}')
async def items(*,
        id: int = Path(..., title='id'),
        q: str,       # 关键字参数，必须传入
    ):
    return {'id': id, 'q': q}
```