Collection update returns the complete document when updating second level key

fabienhuet · August 18, 2016, 6:04pm

My collection structure :

[
	{
		_id: id,
		createdAt: date,
		name: string,
		subObject: {
			id: {
				name: string,
				type: string,
				coordinates: [ [] ], // big
			},
			id: {
				name: string,
				…
		}
	},
	{
		_id: id,
		…

When I update my collection that way :

	Collection.update( {
		_id: targetID,
	}, {
		$set: {
			[ `subObjects.${ id }.type` ]: type,
		},
	} );

Meteor send the complete updated object trough the socket.

Why not… except that subObject is a large collection of coordinates arrays. So the socket send me 1 to 5 mo each time I make an update depending of the target. This is not usable.

Is there a way to ask for atomic updates answers ?

in the socket, the request message is :

["{\"msg\":\"method\",\"method\":\"/collection/update\",\"params\":[{\"_id\":\"dJGDKXuJtWDrgDZgn\"},{\"$set\":{\"subObjects.xxx.type\":\"type_name\"}},{}],\"id\":\"3\"}"]

And the answer :

{"msg":"changed","collection":"geometries","id":"dJGDKXuJtWDrgDZgn","fields":{"subObjects":[{"XXX… and soooo much more

When I update a first level key in my collection object it returns only that key. Why not when I update a second level ?

I tried to make subObject an array instead of an object. Does not fix.

robfallows · August 19, 2016, 9:25am

This is an implementation feature of the diffing algorithm used:

github.com

meteor/meteor/blob/dce2b20ddbe45da48c37f26813fce8d0c72d8c88/packages/diff-sequence/diff.js#L204-L223


// General helper for diff-ing two objects.
// callbacks is an object like so:
// { leftOnly: function (key, leftValue) {...},
//   rightOnly: function (key, rightValue) {...},
//   both: function (key, leftValue, rightValue) {...},
// }
DiffSequence.diffObjects = function (left, right, callbacks) {
_.each(left, function (leftValue, key) {
  if (_.has(right, key))
    callbacks.both && callbacks.both(key, leftValue, right[key]);
  else
    callbacks.leftOnly && callbacks.leftOnly(key, leftValue);
});
if (callbacks.rightOnly) {
  _.each(right, function(rightValue, key) {
    if (!_.has(left, key))
      callbacks.rightOnly(key, rightValue);
  });
}
};

Changes are propagated at the top level only.

fabienhuet · August 20, 2016, 11:04am

Does that mean that the only solution I have is to put every keys of my sub object at the top level ?

robfallows · August 20, 2016, 4:58pm

No. It’s just that the entire top level object is marked as changed, even if only the tip of the object is changed.