Declaring defaults in your schema

Your schemas can define default values for certain paths. If you create a new document without that path set, the default will kick in.

Note: Mongoose only applies a default if the value of the path is strictly undefined.

var schema = new Schema({
  name: String,
  role: { type: String, default: 'guitarist' }
});

var Person = db.model('Person', schema);

var axl = new Person({ name: 'Axl Rose', role: 'singer' });
assert.equal(axl.role, 'singer');

var slash = new Person({ name: 'Slash' });
assert.equal(slash.role, 'guitarist');

var izzy = new Person({ name: 'Izzy', role: undefined });
assert.equal(izzy.role, 'guitarist');

// Defaults do **not** run on `null`, `''`, or value other than `undefined`.
var foo = new Person({ name: 'Bar', role: null });
assert.strictEqual(foo.role, null);

Person.create(axl, slash, function(error) {
  assert.ifError(error);
  Person.find({ role: 'guitarist' }, function(error, docs) {
    assert.ifError(error);
    assert.equal(docs.length, 1);
    assert.equal(docs[0].name, 'Slash');
  });
});

Default functions

You can also set the default schema option to a function. Mongoose will execute that function and use the return value as the default.

var schema = new Schema({
  title: String,
  date: {
    type: Date,
    // `Date.now()` returns the current unix timestamp as a number
    default: Date.now
  }
});

var BlogPost = db.model('BlogPost', schema);

var post = new BlogPost({title: '5 Best Arnold Schwarzenegger Movies'});

// The post has a default Date set to now
assert.ok(post.date.getTime() >= Date.now() - 1000);
assert.ok(post.date.getTime() <= Date.now());

The setDefaultsOnInsert option

By default, mongoose only applies defaults when you create a new document. It will not set defaults if you use update() and findOneAndUpdate(). However, mongoose 4.x lets you opt-in to this behavior using the setDefaultsOnInsert option.

Important

The setDefaultsOnInsert option relies on the MongoDB $setOnInsert operator. The $setOnInsert operator was introduced in MongoDB 2.4. If you're using MongoDB server < 2.4.0, do not use setDefaultsOnInsert.

var schema = new Schema({
  title: String,
  genre: {type: String, default: 'Action'}
});

var Movie = db.model('Movie', schema);

var query = {};
var update = {title: 'The Terminator'};
var options = {
  // Return the document after updates are applied
  new: true,
  // Create a document if one isn't found. Required
  // for `setDefaultsOnInsert`
  upsert: true,
  setDefaultsOnInsert: true
};

Movie.
  findOneAndUpdate(query, update, options, function (error, doc) {
    assert.ifError(error);
    assert.equal(doc.title, 'The Terminator');
    assert.equal(doc.genre, 'Action');
  });

Default functions and this

Unless it is running on a query with setDefaultsOnInsert, a default function's this refers to the document.

const schema = new Schema({
  title: String,
  released: Boolean,
  releaseDate: {
    type: Date,
    default: function() {
      if (this.released) {
        return Date.now();
      }
      return null;
    }
  }
});

const Movie = db.model('Movie', schema);

const movie1 = new Movie({ title: 'The Terminator', released: true });

// The post has a default Date set to now
assert.ok(movie1.releaseDate.getTime() >= Date.now() - 1000);
assert.ok(movie1.releaseDate.getTime() <= Date.now());

const movie2 = new Movie({ title: 'The Legend of Conan', released: false });

// Since `released` is false, the default function will return null
assert.strictEqual(movie2.releaseDate, null);