database-repository-patternlisted

# Database Repository Pattern ## Overview Async SQL with protocol-based repositories. Domain models are plain dataclasses (not ORM entities). Infrastructure-layer implementations handle ORM mapping — domain code never sees it. ## Repository Pattern ```python # Domain layer — pure protocol (in contracts) class UserRepositoryProtocol(Protocol): async def find(self, user_id: str) -> Result[User, NotFoundError]: ... async def save(self, user: User) -> Result[User, DomainError]: ... async def delete(self, user_id: str) -> Result[None, DomainError]: ... # Infrastructure layer — concrete implementation class SqlUserRepository: def __init__(self, db: DatabaseProviderProtocol): self.db = db async def find(self, user_id: str) -> Result[User, NotFoundError]: async with self.db.scoped_context() as conn: row = await conn.fetch_row("SELECT * FROM users WHERE id = $1", user_id) if not row: return Err(UserNotFoundError(user_id)) return Ok(User(id=row["id"], name=row["name"], email=row["email"])) # DI binding container.singleton(UserRepositoryProtocol, SqlUserRepository) ``` ## Domain Models ```python from lexigram.domain import DomainModel @dataclass(frozen=True) class User(DomainModel): id: str name: str email: str ``` `DomainModel` is a mixin providing serialization helpers; it applies `@dataclass(init=False)` automatically when a subclass lacks one (frozen only if you declare it)