MongoDb nested object selection

Question

I have the multiple nested objects and lists, like below

{
 "_id": "5a76be26ca96e22f08af2a19",
 "testId": "123",
 "testName": "summerTest",
 "subjects": [
   {
     "subjectName": "Maths",
     "testDetails": [
     {
      "testNumber": "0001",
      "startTime": "2/18/18 13:30",
      "endTime": "2/18/18 13:30",
      "testDuriation": "01:00:00",
      "questions": [
        {...}
     ]
    },
     {
      "testNumber": "0002",
      "startTime": "2/18/18 13:30",
      "endTime": "2/18/18 13:30",
      "testDuriation": "01:00:00",
      "questions": [
        {...}
     ]
    }
  ]
}

i want to select testNumber 0002 only. using mongoclient in my express js.

collection.find({ "testId": "123", "subjects.subjectName": "Maths", "subjects.testDetails.testNumber": "0002" }).toArray(function (err, data) {}..

But it will return entire TestId 123 document anyone help me. Thanks

from [https://docs.mongodb.com/manual/reference/method/db.collection.find/] (find): Selects documents in a collection or view and returns a cursor to the selected documents. You should use project after find — Luca Rasconi, Feb 09 '18 at 08:12
Already been asked and answered here: https://stackoverflow.com/questions/36229123/return-only-matched-sub-document-elements-within-a-nested-array — , Feb 09 '18 at 10:17

Mauro Piccotti · Answer 1 · 2018-02-09T10:53:40.093

With a find you always return a whole document, so you need to add a projection to only show what you need.

By the way in your find filter there is an error, because if you want to filter only collections with a particular subjects.subjectName and subjects.testDetails.testNumber you need to use $elemMatch (https://docs.mongodb.com/manual/reference/operator/query/elemMatch/). If you don't do this it will return all document where in the subjects array there is one element with the first property and another one with the second property.

score 0 · Answer 2 · answered Feb 09 '18 at 08:34

0

Will be available

db.collection.aggregate([
          {$unwind : '$subjects'},
          {$project : {'_id': 0 , 'array' : '$subjects.testDetails'}},
          {$unwind : '$array'},
          {$match: {'array.testNumber' : '0002' }}
])

answered Feb 09 '18 at 08:34

Spz Sot

3
3

MongoDb nested object selection

2 Answers2