MongoDB：选择两个字段具有相同日期的所有元素

Question

I have a collection like this:

 {
     _id: ObjectId("53c4000f821bc31e3ec90140"),
     foo: "bar",
     created: ISODate("2014-07-09T02:15:49.000+02:00"),
     updated: ISODate("2014-07-09T02:15:49.000+02:00")
 },
 {
     _id: ObjectId("53c4000f821bc4dw3ec90140"),
     foo: "bar",
     created: ISODate("2014-07-09T02:15:49.000+02:00"),
     updated: ISODate("2014-07-09T02:19:49.000+02:00")
 },

Now I want to select all elements of the collection where created == updated . In this example the query should return only the first element.

I tried this: db.foo.find( {$where: "this.created == this.updated"}) but I get no results :-(

Answer 1

Object comparisons don't work like that in JavaScript. You need to compare a "value" and not the whole object:

 db.foo.find(function(){ return this.created.valueOf() == this.updated.valueOf() })

So the .valueOf() is the key here. And that is just a shorthand for $where when you have no other conditions.