Virtualtype

options «Object»
[options.ref] «string|function» if is not nullish, this becomes a
[options.localField] «string|function» the local field to populate on if this is a populated virtual.
[options.foreignField] «string|function» the foreign field to populate on if this is a populated virtual.
[options.justOne=false] «boolean» by default, a populated virtual is an array. If you set justOne, the populated virtual will be a single doc or null.
[options.getters=false] «boolean» if you set this to true, Mongoose will call any custom getters you defined on this virtual
[options.count=false] «boolean» if you set this to true, populate() will set this virtual to the number of populated documents, as opposed to the documents themselves, using Query#countDocuments()
[options.skip=null] «Number» add a default skip to the populate() query
[options.perDocumentLimit=null] «Number» For legacy reasons, with populate() may give incorrect results because it only executes a single query for every document being populated. If you set perDocumentLimit, Mongoose will ensure correct limit per document by executing a separate query for each document to populate(). For example, .find().populate({ path: 'test', perDocumentLimit: 2 }) will execute 2 additional queries if .find() returns 2 documents.
[options.options=null] «Object» Additional options like limit and lean.

VirtualType constructor

This is what mongoose uses to define virtual attributes via Schema.prototype.virtual.

Applies getters to value.

Applies setters to value.

Adds a custom getter to this virtual.

Mongoose calls the getter function with the below 3 parameters.

: the value returned by the previous getter. If there is only one getter, value will be undefined.
virtual: the virtual object you called .get() on
doc: the document this virtual is attached to. Equivalent to this.

Mongoose calls the setter function with the below 3 parameters.