62 lines
2.7 KiB
Python
62 lines
2.7 KiB
Python
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"""统一编号服务 —— 原子取号，替代各处分散扫描式生成（§3.3 编号约定）。
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取号基于 bre_sequence（name/current_seq）表 + PostgreSQL 事务级 advisory lock：
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pg_advisory_xact_lock 在事务内串行化同名取号，锁随事务提交/回滚自动释放，
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与 CRUD 同事务提交 ⇒ 并发请求不重复、失败自动回滚不留空号。
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存量数据迁移：首次使用某序列名时由 seed_fn（服务端传入）从既有记录推算
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起始号（原扫描逻辑），此后全部走原子递增，不再扫描。
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"""
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from typing import Any, Awaitable, Callable
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from sqlalchemy import select, text
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from sqlalchemy.ext.asyncio import AsyncSession
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from app.api.v1.module_bre.sequence.model import SequenceModel
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class NumberGenService:
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"""原子序号发生器。实例化于 HTTP/服务层，随当前事务取号。"""
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def __init__(self, db: AsyncSession) -> None:
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self.db = db
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@staticmethod
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async def _acquire_lock(db: AsyncSession, name: str) -> None:
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from app.config.setting import settings
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if settings.DATABASE_TYPE != "postgres":
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return # sqlite 测试库无 advisory lock，退化为普通自增（单进程无并发竞争）
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# hashtextextended 对文本做稳定 64 位哈希，同名序列恒映射同一把锁
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await db.execute(text("SELECT pg_advisory_xact_lock(hashtextextended(:n, 0))"), {"n": name})
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async def next_seq(
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self,
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name: str,
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*,
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start: int = 1,
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seed_fn: Callable[[], Awaitable[int | None]] | None = None,
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) -> int:
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"""原子取号。返回本序列名下一个应使用的序号。
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name: 序列名（如 "combination:2026" / "tree:3"），按编号维度天然分片；
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start: 新序列的默认起始值；
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seed_fn: 仅当序列行尚不存在时调用，从存量数据推算起始号（兼容既有数据迁移）。
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"""
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await self._acquire_lock(self.db, name)
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row = await self.db.scalar(select(SequenceModel).where(SequenceModel.name == name))
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if row is None:
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init = await seed_fn() if seed_fn is not None else start
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if init is None or init < 1:
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init = start
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self.db.add(SequenceModel(name=name, current_seq=init))
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await self.db.flush()
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return init
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row.current_seq += 1
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await self.db.flush()
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return int(row.current_seq)
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async def exists(self, name: str) -> bool:
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"""序列行是否已初始化（供服务端判断是否需要 seed_fn 兜底）。"""
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return (await self.db.scalar(select(SequenceModel.id).where(SequenceModel.name == name))) is not None
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