MongoDB empty string value vs null value

Question

In MongoDB production, if a value of a key is empty or not provided (optional), should I use empty string value or should I use null for value.

1) Is there any pros vs c

Answer 1

i would say that null indicates absence of the value and empty string indicates that the value is there, but its empty. While reading the data you can distinguish between blank values and non-existing values. Still it depends upon your use-case

Answer 2

I think the best way is undefined as I would suggest not including this key altogether. Mongo doesn't work as SQL, where you have to have at least null in every column. If you don't have value, simply don't include the key. Then if you make query for all documents, where this key doesn't exists it will work correctly, otherwise not. Also if you don't use the key you save a little bit of disk space. Do this is the correct way in Mongo.

function deleteEmpty (v) {
   if(v==null){
     return undefined;
   }
   return v;
}

var UserSchema = new Schema({
email: { type: String, set: deleteEmpty } 
});

Answer 3

This question has been answered at least 4 times by me and a Google search will get you a lot of information.

You must take into consideration what removing the key means. If your document will eventually use that schema in most of its defined state, within the application, then you could be seeing a lot of movement of the document, this neuts the benefit of no having these keys: space. Those couple of bytes you will save in space will be rendered useless and you will get a swiss cheese effect.

However if you do not use these fields at all then having those few extra bytes with millions of documents in your working set could cause real problems that need not be there (if you for some reason want to shove that many documents into your working set), as for the space issue, MongoDB fundamentally has a space issue and I have not really known omitting a couple of keys to do anything to help that.