How to return documents in which two fields have the same value

Question

Is it possible to find only those documents in collections with the same value in two specified fields?

{
    _id:    'fewSFDewvfG20df', 
    start:  10,
    end:    10
}

As used herein startand endhave the same value, the document is selected.

I think of something like ...

Collection.find({ start: { $eq: end } })

... which will not work, as it endshould be a value.

Answer 1

You have two options. The first is to use an operator $where.

Collection.find( { $where: "this.start === this.end" } )

The second option is to use the aggregation structure and the operator $redact.

Collection.aggregate([
    { "$redact": { 
        "$cond": [
            { "$eq": [ "$start", "$end" ] },
            "$$KEEP",
            "$$PRUNE"
        ]
    }}
])

Which one is better?

$where JavaScript , $where . . considerations. $, BSON JavaScript $where, . , , . , .

$redact, $where, , , $redact, MongoDB. , $match.

$where , . , $where, . , .

Answer 2

, ,

Collection.find("this.start == this.end");