It is not possible to set retainKeyOrder option on Model#save()

[bsrykt]

For some cases I want to keep the key order of the data on insert. However this is not possible as Document#toObject() bypasses custom schema options when saving document:

  // When internally saving this document we always pass options,
  // bypassing the custom schema options.
  if (!(options && 'Object' == options.constructor.name)) {
    options = this.schema.options.toObject
      ? clone(this.schema.options.toObject)
      : {};
  }

I think it would be better to make it optional.

[flenter]

We also ran into this problem. The order of keys is especially important when querying on subdocuments (mixed type).

"Equality matches within subdocuments select documents if the subdocument matches exactly the specified subdocument, including the field order."
source: mongodb docs on read operations

Maybe it is a good idea for cloning that the order of keys is always preserved instead of the current implementation (reversing the order of keys to increase cloning speed)?

[alancasagrande]

Same problem as @flenter.

Not sure why reversing is the default implementation and whether there is a reason to not make it optional on saving.

[aheckmann]

JavaScript does not guarantee key order. even in the mongodb shell there's no guarantee let alone when working across languages. key order should not be relied upon.

[pirelenito]

Hi @aheckmann, I agree with you, JavaScript object key order cannot be relied upon, but unfortunately, according to the MongoDB documentation, they do take into account the order of the attributes you pass while querying.

I can't prove this, as I didn't find any reliable reference for the case, but V8 implementation seems to preserve the ordering.

That given, and the available option to retainKeyOrder while cloning the attributes for persistency, I thought a reasonable solution would be to allow defining a schema that "retainKeyOrder" like:

  var Checkin = new Schema({
        date      : Date
      , location  : {
            lat: Number
          , lng: Number
        }
    }, { retainKeyOrder: true });

The default behavior would still be false. But being able to set this, allows us to perform reliably the queries that we need to make our system works.

Do you think that is reasonable? I could make the changes and a provide you with a pull request for evaluation.

Thanks a lot!

[aheckmann]

Sounds reasonable. I'll take a PR with that option disabled.