UnmappedInstanceError: Class 'flask_sqlalchemy.BaseQuery' is not mapped

UnmappedInstanceError: Class 'flask_sqlalchemy.BaseQuery' is not mapped(Flask)

这个错误是因为db.session.add()添加的参数必须为对应的对象。不然会报错

例如：
错误

valuation_id = request.args.get('valuation_id')
    valuation_sys = Valuation_sys.query.filter_by(id=valuation_id)
    if valuation_sys is not None:
        valuation_sys.delete_flag = 1
        db.session.add(valuation_sys)
        return jsonify({'code': '200', 'msg': 'delete success'})
    else:
        
        return jsonify({'code': '10000', 'msg': 'valuation id is not exist'})

正确

valuation_id = request.args.get('valuation_id')
    valuation_sys = Valuation_sys.query.filter_by(id=valuation_id).first()
    if valuation_sys is not None:
        valuation_sys.delete_flag = 1
        db.session.add(valuation_sys)
        return jsonify({'code': '200', 'msg': 'delete success'})
    else:
        
        return jsonify({'code': '10000', 'msg': 'valuation id is not exist'})