Getting first element of embedded array in mongoDB using Node JS driver

Question

Let's say I have the following document stored in a mongoDB collection 'people':

{ 
      _id: 489324,
     name: "Ryan Jones"
   skills: [ "fishing", "programming" ]
}

I am trying to retrieve Ryan Jones's first skill in the array (skills[0]).

This seems like a dead simple operation but I can't seem to do it using the Node JS driver. I can retrieve just the skills array easily:

db.collection('people').findOne({ name:"Ryan Jones"},{ projection: { skills:1 }})

...but I don't want to transfer the whole array over the wire. I just want to get "fishing".

I have tried using slice and arrayElemAt within projection but I get a MongoError. How can I achieve this using the NodeJS driver? Does it require a more complex aggregation operation instead of findOne?

Shubham Dixit · Accepted Answer · 2020-04-25 12:25:43Z

1

You can achieve that with aggregation , with $arrayElemAt something like this

db.collection('people').aggregate([
  {
    $match: {
      name: "Ryan Jones"
    }
  },
  {
    $project: {
      name: 1,
      skills: {
        $arrayElemAt: [
          "$skills",
          0
        ]
      },

    }
  }
])

See demo here

answered Apr 25, 2020 at 12:25

Shubham Dixit

9,2685 gold badges32 silver badges50 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

ddriver1 Over a year ago

Thanks, this aggregation also works and after timing operations vs the findOne method Valijon proposed there is no difference in speed.

Valijon · Accepted Answer · 2020-04-25 12:27:16Z

1

Try this one:

db.collection('people').findOne({
  name: "Ryan Jones"
},
{
  skills: {
    $slice: 1
  }
})

MongoTemplate with .find

answered Apr 25, 2020 at 12:27

Valijon

13.2k4 gold badges40 silver badges74 bronze badges

1 Comment

ddriver1 Over a year ago

I managed to get this to work by wrapping it in { projection : ... } which is needed for the NodeJS driver. However, the default behaviour is to then project the other fields in the document so I had to manually set them to not project, i.e._id:0, name:0

Collectives™ on Stack Overflow

Getting first element of embedded array in mongoDB using Node JS driver

2 Answers 2

1 Comment

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related