第一次提交

app/db.py

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+"""数据库：async engine + session，SQLAlchemy 2.0 声明式基类。"""
+from datetime import datetime, timezone
+
+from sqlalchemy import event
+from sqlalchemy.ext.asyncio import (
+    AsyncSession,
+    async_sessionmaker,
+    create_async_engine,
+)
+from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_column
+
+from app.config import settings
+
+_is_sqlite = settings.database_url.startswith("sqlite")
+
+# SQLite 需要 check_same_thread=False 以配合异步
+engine = create_async_engine(
+    settings.database_url,
+    echo=settings.debug,
+    connect_args={"check_same_thread": False} if _is_sqlite else {},
+)
+
+if _is_sqlite:
+
+    @event.listens_for(engine.sync_engine, "connect")
+    def _sqlite_pragmas(dbapi_conn, _record):
+        """每个连接都要单独设置：WAL 让读写不再互斥，外键约束默认是关的。"""
+        cur = dbapi_conn.cursor()
+        cur.execute("PRAGMA journal_mode=WAL")
+        cur.execute("PRAGMA synchronous=NORMAL")
+        cur.execute("PRAGMA foreign_keys=ON")
+        # 写锁等待，避免并发写直接报 database is locked
+        cur.execute("PRAGMA busy_timeout=5000")
+        cur.close()
+
+SessionLocal = async_sessionmaker(engine, expire_on_commit=False, class_=AsyncSession)
+
+
+class Base(DeclarativeBase):
+    """所有 ORM 模型的基类。"""
+
+
+def _utcnow() -> datetime:
+    return datetime.now(timezone.utc)
+
+
+class TimestampMixin:
+    """通用时间戳字段。
+
+    用 Python 侧的 datetime（带微秒）而非 SQL 的 now()：SQLite 的
+    CURRENT_TIMESTAMP 只精确到秒，同一秒内的多条记录无法排出先后，
+    会让"取最近一次作答"这类查询出错。
+    """
+
+    created_at: Mapped[datetime] = mapped_column(default=_utcnow, nullable=False)
+    updated_at: Mapped[datetime] = mapped_column(
+        default=_utcnow, onupdate=_utcnow, nullable=False
+    )
+
+
+async def get_db():
+    """FastAPI 依赖：提供一个请求级 session。"""
+    async with SessionLocal() as session:
+        yield session