from datetime import datetimefrom fastapi import FastAPI, Depends
from sqlalchemy import DateTime, func, String, Float, select
from sqlalchemy.ext.asyncio import create_async_engine, async_sessionmaker, AsyncSession
from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_columnapp = FastAPI()# 1. 创建异步引擎
ASYNC_DATABASE_URL = "mysql+aiomysql://root:123456@localhost:3306/FastAPI_first?charset=utf8"
async_engine = create_async_engine(ASYNC_DATABASE_URL,echo=True, # 可选，输出 SQL 日志pool_size=10, # 设置连接池活跃的连接数max_overflow=20 # 允许额外的连接数
)# 2. 定义模型类： 基类 + 表对应的模型类
# 基类：创建时间、更新时间；书籍表：id、书名、作者、价格、出版社
class Base(DeclarativeBase):create_time: Mapped[datetime] = mapped_column(DateTime, insert_default=func.now(), default=func.now, comment="创建时间")update_time: Mapped[datetime] = mapped_column(DateTime, insert_default=func.now(), default=func.now, onupdate=func.now(), comment="修改时间")class Book(Base):__tablename__ = "book"id: Mapped[int] = mapped_column(primary_key=True, comment="书籍id")bookname: Mapped[str] = mapped_column(String(255), comment="书名")author: Mapped[str] = mapped_column(String(255), comment="作者")price: Mapped[float] = mapped_column(Float, comment="价格")publisher: Mapped[str] = mapped_column(String(255), comment="出版社")# 3. 建表：定义函数建表 → FastAPI 启动的时候调用建表的函数
async def create_tables():# 获取异步引擎，创建事务 - 建表async with async_engine.begin() as conn:await conn.run_sync(Base.metadata.create_all) # Base 模型类的元数据创建@app.on_event("startup")
async def startup_event():await create_tables()@app.get("/")
async def root():return {"message": "Hello World"}AsyncSessionLocal = async_sessionmaker(bind=async_engine, # 绑定数据库引擎class_=AsyncSession, # 指定会话类expire_on_commit=False # 提交后会话不过期，不会重新查询数据库
)# 依赖项
async def get_database():async with AsyncSessionLocal() as session:try:yield session # 返回数据库会话给路由处理函数await session.commit() # 提交事务except Exception:await session.rollback() # 有异常，回滚raisefinally:await session.close() # 关闭会话@app.get("/book/books")
async def get_book_list(db: AsyncSession = Depends(get_database)):# result = await db.execute(select(Book)) # 查询 → 返回一个 ORM 对象# book = result.scalars().all() # 获取所有# book = result.scalars().first() # 获取第一个book = await db.get(Book, 5) # 获取单条数据 → 根据主键return book
