how to use document fields in query in mongodb

Question

I want to choose documents where from < now and to > (now + delay), where from, to and delay is document fields. Now is my variable. something like that

{
  from: {$gte: now},
  to: {$lte: now + $delay}
}

Himanshu Sharma · Accepted Answer · 2019-09-09 12:35:15Z

1

The following query can get us the expected output:

db.collection.find({
    "from":{
        $gte: now
    },
    $expr:{
        $lte:["$to", { $sum: ["$delay", now] }]
    }
}).pretty()

var now = 2;

Data set:

{
    "_id" : ObjectId("5d7645ab14e02904fe680e12"),
    "from" : 2,
    "to" : 4,
    "delay" : 2
}
{
    "_id" : ObjectId("5d7645ab14e02904fe680e13"),
    "from" : 2,
    "to" : 10,
    "delay" : 2
}
{
    "_id" : ObjectId("5d7645ab14e02904fe680e14"),
    "from" : 6,
    "to" : 10,
    "delay" : 2
}

Output:

{
    "_id" : ObjectId("5d7645ab14e02904fe680e12"),
    "from" : 2,
    "to" : 4,
    "delay" : 2
}

answered Sep 9, 2019 at 12:35

Himanshu Sharma

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1 Comment

Егор Лебедев Over a year ago

Cool, but seems like I got lower version of mongodb where $expr is not supported

OzW · Accepted Answer · 2019-09-10 13:30:34Z

0

If you cannot use $expr you might consider $where.

NOTE: $where has a performance cost.

Example:

db.collection.find({
    $where: function () {
        return this.to > (now + this.delay);
    }
});

this refers to the current document. You can also you obj to reference it.

answered Sep 10, 2019 at 13:30

OzW

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