How to add property to object in array(containing object)?

Question

I am trying to update(add if not present) a property to each object in array in mongodb document. For example

My document :

{
     "_id" : "1",
     student : [
               {
                  "name" : "rajesh",
                   "rollno" : 1
               },
              {
                   name" : "rajesh2",
                   "rollno" : 2
              },
              {
                   name" : "rajesh3",
                   "rollno" : 3,
                   class : 6
             }
       ]
  }

I want to add property 'class' to all the object in student array. How can I do this in mongodb.

What value is class supposed to have?

Joachim Isaksson
– Joachim Isaksson

2014-04-16 11:29:06 +00:00
Commented Apr 16, 2014 at 11:29 — Joachim Isaksson
– Joachim Isaksson, Commented Apr 16, 2014 at 11:29
suppose class value is 7

rajeshpanwar
– rajeshpanwar

2014-04-16 11:30:35 +00:00
Commented Apr 16, 2014 at 11:30 — rajeshpanwar
– rajeshpanwar, Commented Apr 16, 2014 at 11:30

Steve Pitchers · Accepted Answer · 2016-02-17 11:10:08Z

9

Yes and no.

Provided you know the index of the items in the array this is relatively simple:

db.collection.update(
    { "_id": 1 },
    { "$set": {
        "student.0.class": 4,
        "student.1.class": 5,
        "student.2.class": 6
    }}
)

But if you actually wanted to update all of the array values for an unknown length this would not be possible just in single update, so you need to actually retrieve the document and modify the whole array first:

db.collection.find({ _id: 1}).forEach(function(doc) {
    for (var i=0; i < doc.student.length; i++) {
        doc.student[i] = newValue;
    }
    db.collection.update(
        { _id: doc._id },
        { "$set": { "student": doc.student } }
    );    
})

Or some approach basically along those lines.

Know the limitations and code around them appropriately.

edited Feb 17, 2016 at 11:10

Steve Pitchers

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answered Apr 16, 2014 at 11:30

Neil Lunn

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2 Comments

rajeshpanwar Over a year ago

No, this is only example. The number of object in student is unknown.

Neil Lunn Over a year ago

@rajeshpanwar I was adding more information while you commented. Consider the the options and decide on which approach is best for you. You can either read the document and determine the length to construct the first form, or just do the second form.

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