MongoDB, retrieve specific field in array of objects

Question

In my collection I have an array of objects. I'd like to share only a subset of those objects, but I can't find out how to do this?

Here are a few things I tried:

db.collections.find({},
  { fields: {
    'myField': 1, // works
    'myArray': 1, // works
    'myArray.$': 1, // doesn't work
    'myArray.$.myNestedField': 1, // doesn't work
    'myArray.0.myNestedField': 1, // doesn't work
  }
};

That's absolutely correct! Didn't make sense to me to do that. — Florian Bienefelt
– Florian Bienefelt, Commented Jan 12, 2017 at 1:01

s7vr · Accepted Answer · 2017-01-12 01:49:51Z

2

myArray.myNestedField':1 for projecting nested fields from the array.

I'll briefly explain all the variants you have.

'myField': 1 -- Projecting a field value
'myArray': 1 -- Projecting a array as a whole - (Can be scalar, embedded and sub document)

The below variants works only with positional operator($) in the query preceding the projections and projects only the first element matching the query.

'myArray.$': 1
'myArray.$.myNestedField': 1

This is not a valid projection operation.

'myArray.0.myNestedField': 1

More here on how to query & project documents

answered Jan 12, 2017 at 1:49

s7vr

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