mongodb find fields inside an array

Question

I'm trying to learn mongodb, my database looks like this:

    {
        "_id" : ObjectId("625c95836be34e3c73c37316"),
        "cuisine" : "Chinese",
        "grades" : [
            {
                "date" : ISODate("2014-02-25T00:00:00Z"),
                "grade" : "A",
                "score" : 112
            },
            {
                "date" : ISODate("2013-08-14T00:00:00Z"),
                "grade" : "C",
                "score" : 28
            },
            {
                "date" : ISODate("2012-07-18T00:00:00Z"),
                "grade" : "A",
                "score" : 13
            },
            {
                "date" : ISODate("2012-03-09T00:00:00Z"),
                "grade" : "A",
                "score" : 13
            },
            {
                "date" : ISODate("2011-10-27T00:00:00Z"),
                "grade" : "A",
                "score" : 12
            },
            {
                "date" : ISODate("2011-05-19T00:00:00Z"),
                "grade" : "A",
                "score" : 13
            }
        ],
        "name" : "janette"
    },
    {
        "_id" : ObjectId("625c95836be34e3c73c37317"),
        "cuisine" : "Chinese",
        "grades" : [
            {
                "date" : ISODate("2014-01-07T00:00:00Z"),
                "grade" : "A",
                "score" : 17
            },
            {
                "date" : ISODate("2013-05-09T00:00:00Z"),
                "grade" : "B",
                "score" : 107
            }
        ],
        "name" : "Annie'S Kitchen"
    }

each object has an array that owns the same fields. If I try:

db.restaurants.find({"grades.score":{ $gt: 80, $lt: 100 }});

it will catch both but should catch none. Also I want to be able to check:

db.restaurants.find("grades.score":{$gt: 70},"grades.grade":{/^A$/} });

I need to check the fields only with the fields in the same position on the array.

I don't know how to explain it better, sorry, and thanks for the help.

Answer 1

You can use $map to project an auxiliary boolean array and use $allElementsTrue or $anyElementTrue to filter it.

db.restaurants.aggregate([
  {
    "$match": {
      $expr: {
        "$allElementsTrue": {
          "$map": {
            "input": "$grades",
            "as": "g",
            "in": {
              $and: [
                {
                  $gt: [
                    "$$g.score",
                    80
                  ]
                },
                {
                  $lt: [
                    "$$g.score",
                    100
                  ]
                }
              ]
            }
          }
        }
      }
    }
  }
])

Here are the Mongo playgrounds for your first and second query .