Does $project operator modify fields permanently or just for showing the result?

[Rym_Bouchetara]

Hello,
I was wondering if when we use project to edit fields, are they edited as a “view” just in the query or are they edited permanently in the database ?

[steevej (Steeve Juneau)]

This part is correct:

@Rym_Bouchetara

they edited as a “view” just in the query

The database is not modified.

[Rym_Bouchetara]

How about add fields ? Does it add in the database ?

[Santiago_Miranda]

Nope. To write out of the pipeline to a database see $out or $merge

You can also export the result of a query straight from mongoexport or mongodump, which is great.

[Prasad_Saya]

@Rym_Bouchetara, you can use $addFields (or its alias $set) aggreagtion stage in an Update with an Aggregation operation and update the data to the database.