。 {[CastError：投射日期在路径“createdAt”处的值“[object Object]”失败）

Question

我有这段代码：Reviews.find({createdAt : {"$lt" : app.locals.lastDate}})我想动态地将$lt更改为$gt。

app.post("/scroll", function(req, res){ 
    console.log("req.body...", req.body); 
    var sortCreate = req.body.older == true ? "createdAt" : "-createdAt" 
    var greaterOrLess = req.body.older == true ? "$gt" : "$lt"; 
    greaterOrLess = greaterOrLess.toString() 
    console.log("greaterOrLess;;;", greaterOrLess) 
    console.log("inside scroll app.locals.lastDate", app.locals.lastDate) 
    Reviews.find({createdAt : {"$lt" : app.locals.lastDate}}) 
    .limit(10) 
    .sort(sortCreate).exec() 

的问题是，当我改变Reviews.find({createdAt : {"$lt" : app.locals.lastDate}})

到

Reviews.find({createdAt : {greaterOrLess : app.locals.lastDate}})

我得到错误：

{ [CastError: Cast to date failed for value "[object Object]" at path "createdAt 
"] 
    message: 'Cast to date failed for value "[object Object]" at path "createdAt"' 
, 
    name: 'CastError', 
    kind: 'date', 
    value: { greaterOrLess: Sun Aug 07 2016 19:25:48 GMT-0700 (Pacific Daylight Ti 
me) }, 
    path: 'createdAt', 
    reason: undefined } 

这一部分：console.log("greaterOrLess;;;", greaterOrLess)打印出$gt或$lt当我想要那么为什么我不能使用greaterOrLess变量？它看起来像一个字符串，所以我不知道为什么变量操作符不工作。

Answer 1

在对象中不能有动态键。相反，你可以这样做：

var greaterOrLess = req.body.older == true ? {"$gt" : app.locals.lastDate} : {"$lt" : app.locals.lastDate}; 
Reviews.find({createdAt : greaterOrLess})