Is array index position in MongoDB document guaranteed to be maintained for $push operations?

[Mayank Jain]

Hi,

I checked the MongoDB docs but couldn't find the answer to this question.

Is the array index position guaranteed to remain same if you only do $push operations on it?

Example query

db.example.findAndModify({query: { name: "test"},

                         update: { $push: { "mapping.s": "free" }},

                         upsert: true,

                         new: true})

Can the application use the index of the array reliably in this case when fetching the whole doc based on its name?

I am using MongoDB 3.2.x version

Thanks.

[Mayank Jain]

Any updates?

[Rhys Campbell]

From the manual...

"The $position modifier specifies the location in the array at which the $push operator insert elements. Without the $position modifier, the $push operator inserts elements to the end of the array. See $push modifiers for more information."

https://docs.mongodb.org/manual/reference/operator/update/position/#up._S_position

I would say that this means order will be preserved in insert order if you don;t use the $position modifier. There's always the option of using the $position modifier with an index if you wish to be explicit. 

[Mayank Jain]

I thought the same but just wanted to make sure since it does not say this explicitly.

Thanks.