MongoDb: Difference between $push/$addtoset

Question

I read the documentation in the MongoDb and I used a simple proves and I only look that: Push is sorting the array but addtoSet isn\'t it.

For me visual

Answer 1

$push - adds items in the order in which they were received. Also you can add same items several times.

$addToSet - adds just unique items, but order of items is not guaranteed.

If you need to add unique items in order, you can group and add elements via $addToSet, then $unwind the array with elements, $sort by items, and then do $group again with $push items.