options «Object»
[options.ref] «string|function» if ref is not nullish, this becomes a populated virtual
[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.match=null] «Object|Function» add an extra match condition to populate()
[options.limit=null] «Number» add a default limit to the populate() query
[options.skip=null] «Number» add a default skip to the populate() query
[options.perDocumentLimit=null] «Number» For legacy reasons, limit 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.

Example:

const fullname = schema.virtual('fullname');
fullname instanceof mongoose.VirtualType // true

VirtualType.prototype.applyGetters()

Parameters

value «Object»
doc «Document» The document this virtual is attached to

Returns:

«any» the value after applying all getters

Applies getters to value.

VirtualType.prototype.applySetters()

Parameters

value «Object»
doc «Document»

Returns:

«any» the value after applying all setters

Applies setters to value.

VirtualType.prototype.get()

Parameters

VirtualType, «Function(Any|» Document)} fn

Returns:

«VirtualType» this

Adds a custom getter to this virtual.

Mongoose calls the getter function with the below 3 parameters.

value: 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.

Example:

const virtual = schema.virtual('fullname');
virtual.get(function(value, virtual, doc) {
  return this.name.first + ' ' + this.name.last;
});

VirtualType.prototype.set()

Parameters

VirtualType, «Function(Any|» Document)} fn

Returns:

«VirtualType» this

Adds a custom setter to this virtual.

Mongoose calls the setter function with the below 3 parameters.

value: the value being set
virtual: the virtual object you‘re calling .set() on
doc: the document this virtual is attached to. Equivalent to this.

Example:

const virtual = schema.virtual('fullname');
virtual.set(function(value, virtual, doc) {
  const parts = value.split(' ');
  this.name.first = parts[0];
  this.name.last = parts[1];
});

const Model = mongoose.model('Test', schema);
const doc = new Model();
// Calls the setter with `value = 'Jean-Luc Picard'`
doc.fullname = 'Jean-Luc Picard';
doc.name.first; // 'Jean-Luc'
doc.name.last; // 'Picard'