Queries in ES6

Mongoose queries' .exec() function returns a promise, and so its compatible with the ES6 yield keyword and libraries like co.

Note that the yield keyword is currently only supported in NodeJS 0.11.x with the --harmony flag.

exec() integrates with co and the yield keyword

    co(function*() {
      var schema = new Schema({
        eggs: { type: Number, required: true },
        bacon: { type: Number, required: true }
      });

      var Breakfast = db.model('BreakfastHarmony', schema, getCollectionName());

      try {
        yield Breakfast.create(
          { eggs: 4, bacon: 2 },
          { eggs: 3, bacon: 3 },
          { eggs: 2, bacon: 4 });
      } catch(e) {
        return done(e);
      }

      var result;
      try {
        result = yield Breakfast.findOne({ eggs: 4 }).exec();
      } catch(e) {
        return done(e);
      }

      assert.equal(2, result.bacon);

      var results;
      try {
        results = yield Breakfast.find({ eggs: { $gt: 2 } }).sort({ bacon: 1 }).exec();
      } catch(e) {
        return done(e);
      }

      assert.equal(2, results.length);
      assert.equal(2, results[0].bacon);
      assert.equal(3, results[1].bacon);

      var count;
      try {
        count = yield Breakfast.count({ eggs: { $gt: 2 } }).exec();
      } catch(e) {
        return done(e);
      }

      assert.equal(2, count);

      done();
    })();

can call populate() with exec()

    co(function*() {
      var bookSchema = new Schema({
        author: { type: mongoose.Schema.ObjectId, ref: 'AuthorHarmony' },
        title: String
      });

      var authorSchema = new Schema({
        name: String
      });

      var Book = db.model('BookHarmony', bookSchema, getCollectionName());
      var Author = db.model('AuthorHarmony', authorSchema, getCollectionName());

      try {
        var hugo = yield Author.create({ name: 'Victor Hugo' });
        yield Book.create({ author: hugo._id, title: 'Les Miserables' });
      } catch(e) {
        return done(e);
      }

      var result;
      try {
        result = yield Book.findOne({ title: 'Les Miserables' }).populate('author').exec();
      } catch(e) {
        return done(e);
      }

      assert.equal('Victor Hugo', result.author.name);

      done();
    })();