How to remove a field from mongodb collection on update?

Question

How to remove a field from mongodb collection on update?

I know how to remove field from collection:

db.example.update({},{$unset: {field_to_del:1}},false,true)

But I want to delete all document fields where the length is zero when updating document.

javascript
node.js
mongodb

Answer 1

I think you could approach this one of two ways:

1) Know in your app which fields have been removed and remove them on update as you do in your question.

2) Script it as a batch job. This probably does what you need: It forcibly removes any empty field (that is, empty string value) in any document in a collection (collection 'so' in this case)

var updateEmptyField = function(o){ 
   for (var f in o){ 
      if (o[f] === ''){ 
         eval ("db.so.update({},{$unset: {" + f + ":1}},false,true);");
      }
   }
}

db.so.find().forEach(updateEmptyField);

You need to use eval here to use the variable holding the field name.