'can't convert from BSON type long to Date'

分类：uniCloud

uniCloud

            db.collection('kehu').where({  
                user_id:uniCloud.getCurrentUserInfo().uid  
            }).field('dateToString(create_date, "%Y-%m-%d") as yearMonthDayUTC').get().then(res=>{  
                console.log(res);  
            })

报错如图，这样都能报错，是为什么？'can't convert from BSON type long to Date'