3. 通过 loader_filters 改变loader 查询条件

存在一种情况， 我们希望dataloader 中可以添加一些额外的过滤条件，比如我们希望过滤掉标记为deleted 的 comments 和 feedbacks. 或者在某些情况下，查找标为deleted的记录

dataloader filter 参数可以做到

class CommentLoader(DataLoader):
   deleted: bool
   async def batch_load_fn(task_ids):
      async with db.async_session() as session:
            res = await session.execute(select(Comment)
                  .where(Commend.deleted.is_(self.deleted))
                  .where(Comment.task_id.in_(task_ids)))
            rows = res.scalars().all()
            return build_list(rows, task_ids, lambda x: x.task_id)

class FeedbackLoader(DataLoader):
   deleted: bool
   async def batch_load_fn(comment_ids):
      async with db.async_session() as session:
            res = await session.execute(select(Feedback)
               .where(feedback.deleted.is_(self.deleted))
               .where(Feedback.comment_id.in_(comment_ids)))
            rows = res.scalars().all()
            return build_list(rows, comment_ids, lambda x: x.comment_id)

class Task(Base):
   __tablename__ = "task"

   id: Mapped[int] = mapped_column(primary_key=True)
   name: Mapped[str]

class Comment(Base):
   __tablename__ = "comment"

   id: Mapped[int] = mapped_column(primary_key=True)
   task_id: Mapped[int] = mapped_column()
   content: Mapped[str]
   deleted: Mapped[bool]

class Feedback(Base):
   __tablename__ = "feedback"

   id: Mapped[int] = mapped_column(primary_key=True)
   comment_id: Mapped[int] = mapped_column()
   content: Mapped[str]
   deleted: Mapped[bool]

class FeedbackSchema(BaseModel):
   id: int
   comment_id: int
   content: str

   class Config:
      orm_mode = True

class CommentSchema(BaseModel):
   id: int
   task_id: int
   content: str
   feedbacks: List[FeedbackSchema] = []
   def resolve_feedbacks(self, feedback_loader=LoaderDepend(feedback_batch_load_fn)):
      return feedback_loader.load(self.id)

   class Config:
      orm_mode = True

class TaskSchema(BaseModel):
   id: int
   name: str

   comments: List[CommentSchema] = []
   def resolve_comments(self, comment_loader=LoaderDepend(comment_batch_load_fn)):
      return comment_loader.load(self.id)

   class Config:
      orm_mode = True

@app.get('/tasks', response_model=List[TaskSchema])
async def get_tasks(private:bool= Query(default=True),
                  session: AsyncSession = Depends(db.get_session)):
   tasks = (await session.execute(select(Task))).scalars().all()
   loder_filters = {
      CommentLoader: {
         'deleted': False
      },
      FeedbackLoader: {
         'deleted': False
      },
   }

   tasks = await Resolver(loader_filters=loader_filters).resolve(tasks)
   return tasks