Querying nested objects in mongodb

Question

I am trying to query a User collection with multiple nested objects, and I'm not sure how to properly use the projection operators (e.g. $) as they seem to work for arrays not objects.

Each user has a "booksRecords" object, with multiple book objects (e.g. hc_1_3, hc_1_4, etc). Each book object has a field called currLevel and I am trying to find kids that have at least one book object where currLevel: 'nursery'.

I tried doing User.find({'booksRecords.$.currLevel': 'nursery'}), but that doesn't seem to be working and I wonder what is the correct way to query nested objects?

I checked Querying nested in mongoDB, but it is different from my case as I'm querying nested objects.

[
  //first object
  {
    _id: "xxx",
    booksRecords: {
      hc_1_3: {
        markedRead: false,
        currLevel: "elementary"
      },
      hc_1_2: {
        markedRead: false,
        currLevel: "elementary"
      }
    }
  },
  //second object
  {
    _id: "xyz",
    booksRecords: {
      hc_1_3: {
        markedRead: false,
        currLevel: "elementary"
      },
      hc_1_2: {
        markedRead: false,
        currLevel: "nursery"
      }
    }
  }  
]

Alex Blex · Accepted Answer · 2016-03-08 18:55:51Z

1

$ projection applies to array only. You need to use $where to evaluate each document:

db.User.find( { $where: function() {
    for (var i=0 in this.booksRecords) {
        if (this.booksRecords[i].currLevel === 'nursery') {
            return true;
        }
    }
    return false;
} });

answered Mar 8, 2016 at 18:55

Alex Blex

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Comments

HaRLoFei · Accepted Answer · 2016-03-08 18:35:33Z

0

can you please this:

var userList = db.User.find();
var booksRecordsList={};

while(userList.hasNext()){
    var user = userList.next();
    for(var key in user.booksRecords){

        if ( !( key in booksRecordsList ) ) {
        booksRecordsList[key] = key;
        }
    }
};

db.User.find().forEach(function(doc){
    for (var booksRecord in booksRecordsList){
        var booksRecordItem = doc.booksRecords[booksRecord];
        if(booksRecordItem.currLevel == "nursery"){
            print(tojson(doc));
        }
    }
});

answered Mar 8, 2016 at 18:35

HaRLoFei

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