mongodb+nodejs

不能只看mongodb官网文档https://docs.mongodb.com/manual/reference/method/db.collection.findOne/，都是同步接口

要看node的比如http://mongodb.github.io/node-mongodb-native/2.2/api/Collection.html#findOne

var MongoClient = require('mongodb').MongoClient,
  test = require('assert');
MongoClient.connect('mongodb://localhost:27017/test', function(err, db) {
  // Get the collection
  var col = db.collection('find_one_and_delete_with_promise');
  col.insertMany([{a:1, b:1}], {w:1}).then(function(r) {
    test.equal(1, r.result.n);

    col.findOneAndDelete({a:1}
      , { projection: {b:1}, sort: {a:1} }
      ).then(function(r) {
        test.equal(1, r.lastErrorObject.n);
        test.equal(1, r.value.b);

        db.close();
    });
  });
});