Multiple $where queries in MongoDB

Question

I tried to put following query together, but it is not working:

db.sss.find({
    \"pos\": { \"$gte\": 200000, \"$lt\": 2000000 },
    \"$where\": \"(this.chr.le         


        

Answer 1

I guess somewhat you mixed the syntax between JavaScript and MongoDB.
$where executed by JavaScript engine on server side, so your $where statements must conform the syntax of JavaScipt. For example, this.chr.no == 5 is actually this.chr[index].no == 5 as you expected; and a variable is impossibly equal to two different values at the same time. The following codes for your reference:

var judge = function () {
    var unexpect = "X";
    var letter1 = unexpect, letter2 = unexpect;
    for (var i in this.chr) {
        var chr = this.chr[i];
        if (chr.no == 5) {
            letter1 = chr.letter;
        } else if (chr.no == 6) {
            letter2 = chr.letter;
        }
    }
    if (letter1 != letter2 && letter1 != unexpect && letter2 != unexpect) {
        return true;
    }
    return false;
};

db.sss.find({
    "pos": { "$gte": 200000, "$lt": 2000000 },
    "$and" : [{"chr.no" : 5}, {"chr.no" : 6}],    // narrow range further
    "$where": judge
}, {"x_type":1, "sub_name":1, "name":1, "pos":1, "s_type":1, _id:0});

Answer 2

I assume that you have a problem with your $where logic. The way you described it:

(this.chr.letter != "X" && this.chr.no == 5) &&
(this.chr.letter != "X" && this.chr.no == 6) &&
(this.chr.letter != this.chr.letter)

Will return you nothing because this.chr.no can no be 5 and 6 at the same time. Most probably you wanted to have || in between of your brackets.