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

The above condition above I tried to explain below:

• chr.no = 5 and chr.no = 6
• chr.letter between two objects/dicts in chr are not the same and no X, and
• the document must be in range 200000 - 2000000

The example output could look like this:

• {"x_type":"7", "sub_name":"B01", "name":"A", "pos":828288, "s_type":1}
• {"x_type":"9", "sub_name":"B01", "name":"A", "pos":871963, "s_type":3}

Document "x_type":"8" meet not the range condition. Document "x_type":"10" is not valid, because chr.no = 6 has chr.letter = X. And document "x_type":"14" is not valid, because chr.no = 5 and chr.no = 6 both have the same chr.letter = G

The database contains following documents:

{
  "_id":ObjectId("5441b57bb6d08aa98ee8d34f"),
  "name":"A",
  "pos":828288,
  "s_type":1,
  "sub_name":"B01",
  "type":"Test",
  "x_type":7,
  "chr":[
      {
        "letter":"C",
        "no":4
      },
      {
        "letter":"C",
        "no":5
      },
      {
        "letter":"T",
        "no":6
      }
  ]
}{
  "_id":ObjectId("5441b57cb6d08aa98ee8d350"),
  "name":"A",
  "pos":171878,
  "s_type":3,
  "sub_name":"B01",
  "type":"Test",
  "x_type":8,
  "chr":[
      {
        "letter":"C",
        "no":5
      },
      {
        "letter":"T",
        "no":6
      }
  ]
}{
  "_id":ObjectId("5441b57cb6d08aa98ee8d351"),
  "name":"A",
  "pos":871963,
  "s_type":3,
  "sub_name":"B01",
  "type":"Test",
  "x_type":9,
  "chr":[
      {
        "letter":"A",
        "no":5
      },
      {
        "letter":"G",
        "no":6
      }
  ]
}{
  "_id":ObjectId("5441b57cb6d08aa98ee8d352"),
  "name":"A",
  "pos":1932523,
  "s_type":1,
  "sub_name":"B01",
  "type":"Test",
  "x_type":10,
  "chr":[
      {
        "letter":"T",
        "no":4
      },
      {
        "letter":"A",
        "no":5
      },
      {
        "letter":"X",
        "no":6
      }
  ]
}{
  "_id":ObjectId("5441b57cb6d08aa98ee8d353"),
  "name":"A",
  "pos":667214,
  "s_type":1,
  "sub_name":"B01",
  "type":"Test",
  "x_type":14,
  "chr":[
      {
        "letter":"T",
        "no":4
      },
      {
        "letter":"G",
        "no":5
      },
      {
        "letter":"G",
        "no":6
      }
  ]
}

I created the above database with the below script:

from pymongo import MongoClient
from collections import defaultdict


db = MongoClient().test
sDB = db.sss

r = [["Test", "A", "B01", 828288,  1,    7, 'C', 4],
    ["Test", "A", "B01", 828288,  1,    7, 'C', 5],
    ["Test", "A", "B01", 828288,  1,    7, 'T', 6],
    ["Test", "A", "B01", 171878,  3,    8, 'C', 5],
    ["Test", "A", "B01", 171878,  3,    8, 'T', 6],
    ["Test", "A", "B01", 871963,  3,    9, 'A', 5],
    ["Test", "A", "B01", 871963,  3,    9, 'G', 6],
    ["Test", "A", "B01", 1932523, 1,   10, 'T', 4],
    ["Test", "A", "B01", 1932523, 1,   10, 'A', 5],
    ["Test", "A", "B01", 1932523, 1,   10, 'X', 6],
    ["Test", "A", "B01", 667214,  1,   14, 'T', 4],
    ["Test", "A", "B01", 667214,  1,   14, 'G', 5],
    ["Test", "A", "B01", 667214,  1,   14, 'G', 6]]

for i in r:
    sDB.update({'type': i[0],
          'name': i[1],
          'sub_name': i[2],
          'pos': i[3],
          's_type': i[4],
          'x_type': i[5]},
          {"$push": {
              "chr":{
                  "letter":i[6],
                  "no": i[7]} }},
          True)

How is it possible to fix the above query?

Answer 1

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.

Answer 2

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});