MongoDb nested object selection [duplicate]

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 [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
– Luca Rasconi, Commented Feb 9, 2018 at 8:12
Already been asked and answered here: stackoverflow.com/questions/36229123/… — user9251303
– user9251303, Commented Feb 9, 2018 at 10:17

Spz Sot · Accepted Answer · 2018-02-09 08:34:00Z

0

Will be available

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

answered Feb 9, 2018 at 8:34

Spz Sot

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Comments

Mauro Piccotti · Accepted Answer · 2018-02-09 10:53:40Z

0

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.

edited Feb 9, 2018 at 10:53

answered Feb 9, 2018 at 8:22

Mauro Piccotti

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