FastAPI与SQLAlchemy同步数据库集成

# 安装必要库（运行环境要求Python3.7+）
# pip install fastapi sqlalchemy pydantic uvicorn

from sqlalchemy import create_engine, Column, Integer, String, DateTime
from sqlalchemy.ext.declarative import declarative_base
from datetime import datetime

# 创建基类（相当于所有模型的DNA）
Base = declarative_base()


class User(Base):
    __tablename__ = 'users'  # 数据库表名

    id = Column(Integer, primary_key=True, index=True)
    username = Column(String(50), unique=True, nullable=False)
    email = Column(String(100), index=True)
    created_at = Column(DateTime, default=datetime.utcnow)

    def __repr__(self):
        return f"<User {self.username}>"

# 创建数据库引擎（同步模式）
DATABASE_URL = "sqlite:///./test.db"
engine = create_engine(
    DATABASE_URL,
    connect_args={"check_same_thread": False}  # 仅SQLite需要
)

# 创建所有表结构（相当于根据蓝图盖房子）
Base.metadata.create_all(bind=engine)

from sqlalchemy.orm import sessionmaker

# 创建会话工厂（相当于银行窗口）
SessionLocal = sessionmaker(
    autocommit=False,
    autoflush=False,
    bind=engine
)


# 依赖项注入（FastAPI最佳实践）
def get_db():
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()

from fastapi import FastAPI, Depends, HTTPException
from pydantic import BaseModel
from typing import Optional

app = FastAPI()


# Pydantic模型（数据验证层）
class UserCreate(BaseModel):
    username: str
    email: Optional[str] = None


class UserResponse(UserCreate):
    id: int
    created_at: datetime


# 创建用户端点
@app.post("/users/", response_model=UserResponse)
def create_user(user: UserCreate, db: Session = Depends(get_db)):
    # 检查用户名是否重复
    db_user = db.query(User).filter(User.username == user.username).first()
    if db_user:
        raise HTTPException(status_code=400, detail="Username already registered")

    # 创建ORM对象
    db_user = User(**user.dict())
    db.add(db_user)
    db.commit()
    db.refresh(db_user)
    return db_user

@app.get("/users/{user_id}", response_model=UserResponse)
def read_user(user_id: int, db: Session = Depends(get_db)):
    user = db.query(User).filter(User.id == user_id).first()
    if not user:
        raise HTTPException(status_code=404, detail="User not found")
    return user

from sqlalchemy import Index


class Product(Base):
    __tablename__ = 'products'
    id = Column(Integer, primary_key=True)
    name = Column(String(100))
    category = Column(String(50))
    price = Column(Integer)


# 创建复合索引（名称+类别）
__table_args__ = (
    Index('idx_name_category', 'name', 'category'),
)

def transfer_funds(sender_id, receiver_id, amount, db):
    try:
        sender = db.query(User).get(sender_id)
        receiver = db.query(User).get(receiver_id)

        if sender.balance < amount:
            raise ValueError("Insufficient balance")

        sender.balance -= amount
        receiver.balance += amount

        db.commit()
    except:
        db.rollback()
        raise