nonebot2/website/docs/best-practice/database/developer/dependency.md

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---
sidebar_position: 3
description: 依赖注入
---
# 依赖注入
`nonebot-plugin-orm` 提供了强大且灵活的依赖注入,可以方便地帮助你获取数据库会话和查询数据。
## 数据库会话
### AsyncSession
新数据库会话,常用于有独立的数据库操作逻辑的插件。
```python {13,26}
from nonebot import on_message
from nonebot.params import Depends
from nonebot_plugin_orm import AsyncSession, Model, async_scoped_session
from sqlalchemy.orm import Mapped, mapped_column
message = on_message()
class Message(Model):
id: Mapped[int] = mapped_column(primary_key=True, autoincrement=True)
async def get_message(session: AsyncSession) -> Message:
# 等价于 session = get_session()
async with session:
msg = Message()
session.add(msg)
await session.commit()
await session.refresh(msg)
return msg
@message.handle()
async def _(session: async_scoped_session, msg: Message = Depends(get_message)):
await session.rollback() # 无法回退 get_message() 中的更改
await message.send(str(msg.id)) # msg 被存储msg.id 递增
```
### async_scoped_session
数据库作用域会话,常用于事件响应器和有与响应逻辑相关的数据库操作逻辑的插件。
```python {1326}
from nonebot import on_message
from nonebot.params import Depends
from nonebot_plugin_orm import Model, async_scoped_session
from sqlalchemy.orm import Mapped, mapped_column
message = on_message()
class Message(Model):
id: Mapped[int] = mapped_column(primary_key=True, autoincrement=True)
async def get_message(session: async_scoped_session) -> Message:
# 等价于 session = get_scoped_session()
msg = Message()
session.add(msg)
await session.flush()
await session.refresh(msg)
return msg
@message.handle()
async def _(session: async_scoped_session, msg: Message = Depends(get_message)):
await session.rollback() # 可以回退 get_message() 中的更改
await message.send(str(msg.id)) # msg 没有被存储msg.id 不变
```
## 查询数据
### Model
支持类作为依赖。
```python
from typing import Annotated
from nonebot.params import Depends
from nonebot_plugin_orm import Model
from sqlalchemy.orm import Mapped, mapped_column
def get_id() -> int: ...
class Message(Model):
id: Annotated[Mapped[int], Depends(get_id)] = mapped_column(
primary_key=True, autoincrement=True
)
async def _(msg: Message):
# 等价于 msg = (
# await (await session.stream(select(Message).where(Message.id == get_id())))
# .scalars()
# .one_or_none()
# )
...
```
### SQLDepends
参数为一个 SQL 语句决定依赖注入的内容SQL 语句中可以使用子依赖。
```python {11-13}
from nonebot.params import Depends
from nonebot_plugin_orm import Model, SQLDepends
from sqlalchemy import select
def get_id() -> int: ...
async def _(
model: Model = SQLDepends(select(Model).where(Model.id == Depends(get_id))),
): ...
```
参数可以是任意 SQL 语句,但不建议使用 `select` 以外的语句,因为语句可能没有返回值(`returning` 除外),而且代码不清晰。
### 类型标注
类型标注决定依赖注入的数据结构,主要影响以下几个层面:
- 迭代器(`session.execute()`)或异步迭代器(`session.stream()`
- 标量(`session.execute().scalars()`)或元组(`session.execute()`
- 一个(`session.execute().one_or_none()`,注意 `None` 时可能触发 [重载](../../../appendices/overload#重载))或全部(`session.execute()` / `session.execute().all()`
- 连续(`session().execute()`)或分块(`session.execute().partitions()`
具体如下(可以使用父类型作为类型标注):
- ```python
async def _(rows_partitions: AsyncIterator[Sequence[Tuple[Model, ...]]]):
# 等价于 rows_partitions = await (await session.stream(sql).partitions())
async for partition in rows_partitions:
for row in partition:
print(row[0], row[1], ...)
```
- ```python
async def _(model_partitions: AsyncIterator[Sequence[Model]]):
# 等价于 model_partitions = await (await session.stream(sql).scalars().partitions())
async for partition in model_partitions:
for model in partition:
print(model)
```
- ```python
async def _(row_partitions: Iterator[Sequence[Tuple[Model, ...]]]):
# 等价于 row_partitions = await session.execute(sql).partitions()
for partition in rows_partitions:
for row in partition:
print(row[0], row[1], ...)
```
- ```python
async def _(model_partitions: Iterator[Sequence[Model]]):
# 等价于 model_partitions = await (await session.execute(sql).scalars().partitions())
for partition in model_partitions:
for model in partition:
print(model)
```
- ```python
async def _(rows: sa_async.AsyncResult[Tuple[Model, ...]]):
# 等价于 rows = await session.stream(sql)
async for row in rows:
print(row[0], row[1], ...)
```
- ```python
async def _(models: sa_async.AsyncScalarResult[Model]):
# 等价于 models = await session.stream(sql).scalars()
async for model in models:
print(model)
```
- ```python
async def _(rows: sa.Result[Tuple[Model, ...]]):
# 等价于 rows = await session.execute(sql)
for row in rows:
print(row[0], row[1], ...)
```
- ```python
async def _(models: sa.ScalarResult[Model]):
# 等价于 models = await session.execute(sql).scalars()
for model in models:
print(model)
```
- ```python
async def _(rows: Sequence[Tuple[Model, ...]]):
# 等价于 rows = await (await session.stream(sql).all())
for row in rows:
print(row[0], row[1], ...)
```
- ```python
async def _(models: Sequence[Model]):
# 等价于 models = await (await session.stream(sql).scalars().all())
for model in models:
print(model)
```
- ```python
async def _(row: Tuple[Model, ...]):
# 等价于 row = await (await session.stream(sql).one_or_none())
print(row[0], row[1], ...)
```
- ```python
async def _(model: Model):
# 等价于 model = await (await session.stream(sql).scalars().one_or_none())
print(model)
```