模式中生命默认值

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

    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');

默认函数

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());

setDefaultsOnInsert 选项

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.

重要

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');
      });