feat: bootstrap dodo phase one

backend/db.py

@@ -0,0 +1,41 @@
+from collections.abc import AsyncIterator
+
+from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine
+from sqlalchemy.orm import DeclarativeBase
+
+from .config import get_settings
+
+
+class Base(DeclarativeBase):
+    pass
+
+
+_engine = None
+_session_factory = None
+
+
+def get_engine():
+    global _engine, _session_factory
+    if _engine is None:
+        _engine = create_async_engine(get_settings().database_url, pool_pre_ping=True)
+        _session_factory = async_sessionmaker(_engine, expire_on_commit=False)
+    return _engine
+
+
+def reset_engine() -> None:
+    global _engine, _session_factory
+    _engine = None
+    _session_factory = None
+
+
+async def get_db() -> AsyncIterator[AsyncSession]:
+    get_engine()
+    assert _session_factory is not None
+    async with _session_factory() as session:
+        yield session
+
+
+async def create_schema() -> None:
+    from . import models  # noqa: F401
+    async with get_engine().begin() as conn:
+        await conn.run_sync(Base.metadata.create_all)