パスパラメーター、クエリパラメーター、リクエストボディ

パスパラメータの検証

from fastapi import FastAPI, Path
app = FastAPI()

@app.get("/items/{item_id}")
def get_item(item_id: int = Path(ge=1, le=1000)):
    return {"item_id": item_id}

# GET /items/0  → 422 (must be >= 1)

クエリパラメータの検証

from fastapi import FastAPI, Query
app = FastAPI()

@app.get("/search")
def search(
    q: str = Query(min_length=2, max_length=50),
    page: int = Query(default=1, ge=1),
):
    return {"q": q, "page": page}

オプションのクエリパラメータ

from fastapi import FastAPI
app = FastAPI()

@app.get("/users")
def list_users(
    dept: str | None = None,
    active: bool = True
):
    return {"dept": dept, "active": active}

# GET /users → dept=None, active=True
# GET /users?dept=HR&active=false

1 つのクエリパラメータに対する複数の値

from fastapi import FastAPI, Query
from typing import Annotated
app = FastAPI()

@app.get("/filter")
def filter_items(tags: Annotated[list[str], Query()] = []):
    return {"tags": tags}

# GET /filter?tags=python&tags=web

ネストしたリクエストボディ

from fastapi import FastAPI
from pydantic import BaseModel
app = FastAPI()

class Address(BaseModel):
    street: str
    city: str

class User(BaseModel):
    name: str
    address: Address

@app.post("/users")
def create_user(user: User):
    return user.model_dump()

Pydantic のフィールド制約

from pydantic import BaseModel, Field

class Product(BaseModel):
    name: str = Field(min_length=1, max_length=100)
    price: float = Field(gt=0)
    quantity: int = Field(ge=0, default=0, description="Items in stock")

リクエストボディ・パス・クエリの組み合わせ

from fastapi import FastAPI
from pydantic import BaseModel
app = FastAPI()

class ItemUpdate(BaseModel):
    name: str
    price: float

@app.put("/shops/{shop_id}/items/{item_id}")
def update_item(
    shop_id: int,
    item_id: int,
    item: ItemUpdate,
    notify: bool = False,
):
    return {"shop": shop_id, "item": item_id,
            "data": item.model_dump(), "notify": notify}

ファイルのアップロード

from fastapi import FastAPI, UploadFile, File
app = FastAPI()

@app.post("/upload")
async def upload(file: UploadFile = File(...)):
    content = await file.read()
    return {"filename": file.filename, "size": len(content)}

フォームデータ

# pip install python-multipart
from fastapi import FastAPI, Form
app = FastAPI()

@app.post("/login")
def login(username: str = Form(...), password: str = Form(...)):
    return {"username": username}

リクエスト検証のまとめ

# Auto-validated:
# - Path params: type coercion, Path() constraints
# - Query params: Query() constraints, type coercion
# - Request body: Pydantic model validation
# - All errors → HTTP 422 Unprocessable Entity
# - No manual validation needed

エイリアスと非推奨化

from fastapi import FastAPI, Query
app = FastAPI()

@app.get("/items")
def get_items(
    q: str | None = Query(default=None, alias="search-query"),
    old: str | None = Query(default=None, deprecated=True),
):
    return {"q": q, "old": old}

# GET /items?search-query=python

確認問題

復習