Using variables in MongoDB update statement

Question

I am trying to use a variable as the field name in an update statement and it is not working at all, any suggestions?

for example:

COLLECTIONNAME.update(
    { _id: this._id },
    { $set: { VARIABLE1 : VARIABLE2 } }
);

actual code:

 'blur .editable' : function () {
      var target = event.currentTarget.value;
      var field = event.currentTarget.name;
      field = ' " ' + field + ' " ';
      Hostings.update( { _id: this._id },{ $set: { field : target } } );
    }

Jonathan Crowe · Accepted Answer · 2013-08-29T19:08:52.397

14

You can do it this way:

'blur .editable' : function () {
  var target = event.currentTarget.value;
  var field = event.currentTarget.name;

  var obj = {};
      obj[field] = target;
  Hostings.update( { _id: this._id },{ $set: obj } );
}

Javascrip objects can be accessed two ways:

object.attribute

or

object["attribute"]

if you use the second method you can access it with a variable

edited Aug 29 '13 at 19:08

answered Aug 29 '13 at 06:29

Jonathan Crowe

5,793
1
18
28

beautiful! I just had to remove this line: field = ' " ' + field + ' " '; and it worked perfectly. Thanks so much! – glasses Aug 29 '13 at 06:48
3

`Hostings.update( { _id: this._id },{ $set: { [field]: target } } );` Would also work – L. Norman Dec 10 '18 at 21:57
How does `[]`work internally? Does it enforce mongo to use the `key` from outside the anonymous function? Why is it not needed for the `value` ? – Timo Apr 15 '22 at 08:59

score 5 · Answer 2 · answered Apr 06 '20 at 02:41

5

As per L. Norman's comment, I find using the [] for the field value works instead

collection = "my_collection"
db.getCollection(collection).find({}).forEach(function(doc) {
    var new_field = "new_field";
    var new_value = "new_value";

    db.getCollection(collection).update({_id: doc._id}, 
        {$set: {[new_field] : new_value}}) 
})

answered Apr 06 '20 at 02:41

Yi Xiang Chong

744
11
9

This was the simplest solution that worked. Placing the field value in [ ] was the solution to the same issue I was having. – timv Sep 21 '21 at 23:52

score 1 · Answer 3 · answered Mar 04 '14 at 23:12

for your query
COLLECTIONNAME.update( { _id: this._id },{ $set: { VARIABLE1 : VARIABLE2 } } ); mongodb will take value of VARIABLE2 but it will consider "VARIABLE1" to be a field in the document.

For passing a variable whose value is a field name:

you will have to create a javascript object and use it as follows:

var obj={};
obj[VARIABLE1] = VARIABLE2; //where VARIABLE1 and VARIABLE2 are getting values from elsewhere earlier

If you want to have multiple fields this way, just add it to the same object:

obj[VARIABLE3]= VARIABLE4;

Then do update operation as:

db.collectionname.update( { _id: this._id },{ $set: obj } );

Using variables in MongoDB update statement

3 Answers3

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