Model - Model.populate() - 《Mongoose ODM v5.11.15 Documentation》

options «Object|String» Either the paths to populate or an object specifying all parameters
[options.retainNullValues=false] «boolean» By default, Mongoose removes null and undefined values from populated arrays. Use this option to make retain null and undefined array entries.
[options.clone=false] «boolean» When you do , blog posts with the same author will share 1 copy of an author doc. Enable this option to make Mongoose clone populated docs before assigning them.
[options.match=null] «Object|Function» Add an additional filter to the populate query. Can be a filter object containing MongoDB query syntax, or a function that returns a filter object.
[options.skipInvalidIds=false] «Boolean» By default, Mongoose throws a cast error if localField and foreignField schemas don’t line up. If you enable this option, Mongoose will instead filter out any localField properties that cannot be casted to foreignField‘s schema type.
[callback(err,doc)] «Function» Optional callback, executed upon completion. Receives err and the .

Populates document references.

path: space delimited path(s) to populate
select: optional fields to select
match: optional query conditions to match
model: optional name of the model to use for population
justOne: optional boolean, if true Mongoose will always set path to an array. Inferred from schema by default.

Model.populate()