fix bugs (#662)

### What problem does this PR solve?

Fix import error for task_service.py

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

api/apps/document_app.py

 from api.settings import RetCode
 from api.utils.api_utils import get_json_result
 from rag.utils.minio_conn import MINIO
-from rag.utils.redis_conn import REDIS_CONN
 from api.utils.file_utils import filename_type, thumbnail
-from rag.settings import SVR_QUEUE_NAME
 
 
 @manager.route('/upload', methods=['POST'])

api/db/services/task_service.py

 from api.db.services.document_service import DocumentService
 from api.utils import current_timestamp, get_uuid
 from deepdoc.parser.excel_parser import RAGFlowExcelParser
-from rag.settings import MINIO, SVR_QUEUE_NAME
+from rag.settings import SVR_QUEUE_NAME
+from rag.utils.minio_conn import MINIO
 from rag.utils.redis_conn import REDIS_CONN
 
 
 class TaskService(CommonService):
     model = Task
 
+    @classmethod
+    @DB.connection_context()
     def get_tasks(cls, task_id):
         fields = [
             cls.model.id,