mongodb query for finding distinct value in array

Question

Created a collection for the array “test”

({a:"foo", b:[10,20,30]}) 
({a:"foo", b:[15,25,35]}) 
({a:"foo", b:[10,40,50]}) 
({a:"bar", b:[10,60,70]})

MongoDB query to find all documents which has the a distinct values and b value as “10”.

I have tried this

db.test.find({b: {$elemMatch : {$in : [10] }}})

{ "_id" : ObjectId("5bda7ea8aabd746c974b5faa"), "a" : "foo", "b" : [ 10, 20, 30 ] }
{ "_id" : ObjectId("5bda7f74aabd746c974b5fac"), "a" : "foo", "b" : [ 10, 40, 50 ] }
{ "_id" : ObjectId("5bda7f74aabd746c974b5fad"), "a" : "bar", "b" : [ 10, 60, 70 ] }

this is giving output of second one, how to get distinct value of a?

Pang · Accepted Answer · 2018-11-01 06:35:40Z

1

I got my answer.

db.test.distinct( "a" , {b: {$elemMatch : {$in : [10] }}})

Output:

[ "foo", "bar" ]

edited Nov 1, 2018 at 6:35

Pang

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answered Nov 1, 2018 at 6:10

Pallavi

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Comments

Ayush Gupta · Accepted Answer · 2018-11-01 05:38:52Z

0

db.collection.aggregate([{
    $unwind: "$b"
  },
  {
    $group: {
      _id: "$b",
      a_vals: {
        $addToSet: "$a"
      },
      count: {
        $sum: 1
      }
    }
  },
  {
    $match: {
      count: {
        $gt: 1
      }
    }
  }
]);

Playground link: https://mongoplayground.net/p/qR2mTqXPs3o

answered Nov 1, 2018 at 5:38

Ayush Gupta

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