refactor: update migration paths and improve database operation handling

backend/app/db/queryset.py

@@ -0,0 +1,43 @@
+from __future__ import annotations
+
+from dataclasses import dataclass, replace
+from typing import Any, Generic, TypeVar
+
+from sqlmodel import select
+from sqlmodel.ext.asyncio.session import AsyncSession
+from sqlmodel.sql.expression import SelectOfScalar
+
+ModelT = TypeVar("ModelT")
+
+
+@dataclass(frozen=True)
+class QuerySet(Generic[ModelT]):
+    statement: SelectOfScalar[ModelT]
+
+    def filter(self, *criteria: Any) -> QuerySet[ModelT]:
+        return replace(self, statement=self.statement.where(*criteria))
+
+    def order_by(self, *ordering: Any) -> QuerySet[ModelT]:
+        return replace(self, statement=self.statement.order_by(*ordering))
+
+    def limit(self, value: int) -> QuerySet[ModelT]:
+        return replace(self, statement=self.statement.limit(value))
+
+    def offset(self, value: int) -> QuerySet[ModelT]:
+        return replace(self, statement=self.statement.offset(value))
+
+    async def all(self, session: AsyncSession) -> list[ModelT]:
+        return list(await session.exec(self.statement))
+
+    async def first(self, session: AsyncSession) -> ModelT | None:
+        return (await session.exec(self.statement)).first()
+
+    async def one_or_none(self, session: AsyncSession) -> ModelT | None:
+        return (await session.exec(self.statement)).one_or_none()
+
+    async def exists(self, session: AsyncSession) -> bool:
+        return await self.limit(1).first(session) is not None
+
+
+def qs(model: type[ModelT]) -> QuerySet[ModelT]:
+    return QuerySet(select(model))