Check existence of unknown field in array

Question

i have this data from a MongoDB database, i want to return all the objects from the array "Books" and how to query for a specific book inside this array ?

{
  "_id": {
    "$oid": "5b193757fb6fc05a6fe42330"
  },
  "Books": [
    {
      "Me Talk Pretty One Day ": {
        "_id": 312
      }
    },
    {
      "One Hundred Years of Solitude ": {
        "_id": 123
      }
    }
  ]
}

Do you want to return specific book or whole array? please post your sample output — Ashh, Jun 09 '18 at 18:25
I had to use another type of query, it seems that placing the query as find( query, projection ) doesn't work anymore, i had to do find(query).project(projection) — Bruno Cerk, Jun 15 '18 at 03:53

Ashh · Accepted Answer · 2018-06-09T19:55:56.070

1

If you want to retrive specific book from the array you can try this

db.collection.find({
  Books: {
    $elemMatch: {
      "Me Talk Pretty One Day": {
        $exists: true
      }
    }
  }
},
{
  Books: {
    $elemMatch: {
      "Me Talk Pretty One Day": {
        $exists: true
      }
    }
  }
})

edited Jun 09 '18 at 19:55

answered Jun 09 '18 at 19:19

Ashh

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Check existence of unknown field in array

1 Answers1