How to Create Virtuals in Mongoose: Simple Guide

In Mongoose, you create a virtual property using schema.virtual('name') and define a getter function with .get(). Virtuals let you add fields that are computed dynamically and not saved in the database.

Syntax

To create a virtual in Mongoose, use schema.virtual('virtualName') to define the virtual field. Then use .get(function() { ... }) to specify how to compute its value.

This virtual field will not be saved in the database but will appear when you convert documents to JSON or objects.

javascript

const mongoose = require('mongoose');

const schema = new mongoose.Schema({
  firstName: String,
  lastName: String
});

schema.virtual('fullName').get(function() {
  return this.firstName + ' ' + this.lastName;
});

Example

This example shows how to create a virtual property fullName that combines firstName and lastName. The virtual is accessible like a normal property but is not stored in MongoDB.

javascript

const mongoose = require('mongoose');

const userSchema = new mongoose.Schema({
  firstName: String,
  lastName: String
});

userSchema.virtual('fullName').get(function() {
  return this.firstName + ' ' + this.lastName;
});

const User = mongoose.model('User', userSchema);

const user = new User({ firstName: 'Jane', lastName: 'Doe' });

console.log(user.fullName);

Output

Jane Doe

Common Pitfalls

• Virtuals are not saved to the database, so they won't appear if you query raw MongoDB.
• By default, virtuals do not show up in toJSON() or toObject() outputs unless you enable them in the schema options.
• Trying to set a virtual property without a setter will not change the underlying data.

javascript

const mongoose = require('mongoose');

const schema = new mongoose.Schema({
  firstName: String,
  lastName: String
}, { toJSON: { virtuals: true }, toObject: { virtuals: true } });

schema.virtual('fullName').get(function() {
  return this.firstName + ' ' + this.lastName;
});

// Without the toJSON/toObject options, fullName won't appear in JSON output

const user = new mongoose.model('User', schema)({ firstName: 'John', lastName: 'Smith' });

console.log(JSON.stringify(user)); // fullName missing
console.log(JSON.stringify(user.toJSON())); // fullName included

Output

{"firstName":"John","lastName":"Smith"}
{"firstName":"John","lastName":"Smith","fullName":"John Smith"}

Quick Reference

Remember these key points when working with Mongoose virtuals:

• Use schema.virtual('name').get(fn) to define a virtual getter.
• Virtuals are not stored in MongoDB.
• Enable { toJSON: { virtuals: true }, toObject: { virtuals: true } } in schema options to include virtuals in output.
• You can also define setters with .set(fn) if needed.

Key Takeaways

Create virtuals with schema.virtual('name').get(function) to add computed fields.

Virtuals do not save data to MongoDB but appear in document objects.

Enable virtuals in JSON output with schema options { toJSON: { virtuals: true } }.

Virtual setters allow modifying underlying data through virtual properties.

Without enabling virtuals in output, they won't appear when converting documents to JSON.