If a class is needed, instead create a regular function dependency that returns a class instance.

Do this:

```python
from dataclasses import dataclass
from typing import Annotated

from fastapi import Depends, FastAPI

app = FastAPI()


@dataclass
class DatabasePaginator:
    offset: int = 0
    limit: int = 100
    q: str | None = None

    def get_page(self) -> dict:

You can also use `dataclasses` in the `response_model` parameter:

{* ../../docs_src/dataclasses_/tutorial002_py310.py hl[1,6:12,18] *}

The dataclass will be automatically converted to a Pydantic dataclass.

This way, its schema will show up in the API docs user interface:

<img src="/img/tutorial/dataclasses/image01.png">

from dataclasses import field  # (1)

from fastapi import FastAPI
from pydantic.dataclasses import dataclass  # (2)


@dataclass
class Item:
    name: str
    description: str | None = None


@dataclass
class Author:
    name: str
    items: list[Item] = field(default_factory=list)  # (3)


app = FastAPI()


@app.post("/authors/{author_id}/items/", response_model=Author)  # (4)

from dataclasses import dataclass

from fastapi import FastAPI


@dataclass
class Item:
    name: str
    price: float
    description: str | None = None
    tax: float | None = None


app = FastAPI()


@app.post("/items/")
async def create_item(item: Item):

from dataclasses import dataclass, field

from fastapi import FastAPI


@dataclass
class Item:
    name: str
    price: float
    tags: list[str] = field(default_factory=list)
    description: str | None = None
    tax: float | None = None


app = FastAPI()


@app.get("/items/next", response_model=Item)
async def read_next_item():
    return {
        "name": "Island In The Moon",
        "price": 12.99,

from __future__ import annotations

import uuid
from dataclasses import dataclass, field

from dirty_equals import IsUUID
from fastapi import FastAPI
from fastapi.testclient import TestClient
from inline_snapshot import snapshot


@dataclass
class Item:
    id: uuid.UUID
    name: str
    price: float
    tags: list[str] = field(default_factory=list)
    description: str | None = None
    tax: float | None = None

import inspect
import sys
from collections.abc import Callable
from dataclasses import dataclass, field
from functools import cached_property, partial
from typing import Any, Literal

from fastapi._compat import ModelField
from fastapi.security.base import SecurityBase
from fastapi.types import DependencyCacheKey

if sys.version_info >= (3, 13):  # pragma: no cover
    from inspect import iscoroutinefunction
else:  # pragma: no cover

import warnings
from collections import deque
from dataclasses import dataclass
from datetime import datetime, timezone
from decimal import Decimal
from enum import Enum
from math import isinf, isnan
from pathlib import PurePath, PurePosixPath, PureWindowsPath
from typing import TypedDict

import pytest
from fastapi._compat import Undefined
from fastapi.encoders import jsonable_encoder
from fastapi.exceptions import PydanticV1NotSupportedError

3. Dataclass `Author` содержит список dataclass `Item`.

4. Dataclass `Author` используется в параметре `response_model`.

5. Вы можете использовать и другие стандартные аннотации типов вместе с dataclasses в качестве тела запроса.

    В этом случае это список dataclass `Item`.

6. Здесь мы возвращаем словарь, содержащий `items`, который является списком dataclass.

1. 依然として標準の `dataclasses` から `field` をインポートします。

2. `pydantic.dataclasses` は `dataclasses` のドロップイン置換です。

3. `Author` dataclass は `Item` dataclass のリストを含みます。

4. `Author` dataclass を `response_model` パラメータとして使用しています。

5. リクエストボディとしての dataclass と併せて、他の標準の型注釈を使用できます。

    この例では、`Item` dataclass のリストです。

6. ここでは、dataclass のリストである `items` を含む辞書を返しています。

    FastAPI はデータを JSON に <dfn title="送信可能な形式にデータを変換すること">シリアライズ</dfn> できます。