停止执行进一步的代码

时间:2018-05-31 02:10:53

标签: javascript node.js mongodb mongoose

我有一个请求:

  Character.count({'character.ownerid': msg.author.id}, function (err, count) {
    if (err) {
      throw err;
    }

    if (count > 3) {
      err.message = 'Too many characters';
      //create error explanation and throw it
      throw err;
    }
  })

如果确实发生任何错误,我需要退出整个父函数。我不能在此请求中返回,因为它只退出此方法。我认为有可能做一个回调,如:

Character.count({'character.ownerid': msg.author.id}, function (err, count, stop) {

但如何使用呢?它在匿名函数中,我不知道在哪里放置它的内容。我还尝试使用try / catch,但由于Error: Unhandled "error" event. ([object Object])我无法向外部处理程序抛出错误,请参阅下面的代码:

Character.count({'character.ownerid': msg.author.id}, function (err, count) {
  if (err) {
    throw err;
  }

  if (count > 3) {
    var err = {};
    err.message = 'Too many characters';
    throw err;
  }
}).then((count) => {
  console.log('all good we may continue');
  console.log(count);
}).catch((err) => {
  if (err != undefined && err.length > 0) {
    msg.reply(err.message);
    return 0; //exit parent function?
  }
});

但即使这有效,我也不确定这段代码是否能满足我的需要。请求是异步的,那么如果其余的代码在then之前被触发呢?这甚至可能吗?

所以我基本上需要以某种方式return 0;父函数,如果有任何错误,我需要为它们设置一个处理程序。有什么想法吗?

1 个答案:

答案 0 :(得分:2)

你似乎错过了这个概念。首先,如前所述,所有的猫鼬行动都会返回一个承诺或至少一个承诺,就像#34;可以通过then()立即解析而不是传入回调函数的对象。这可以通过两种方式呈现。

使用async/await语法和try..catch块:

const { Schema } = mongoose = require('mongoose');

const uri = 'mongodb://localhost/test';

mongoose.set('debug', true);
mongoose.Promise = global.Promise;

const characterSchema = new Schema({
  name: String
});

const Character = mongoose.model('Character', characterSchema);

const log = data => console.log(JSON.stringify(data,undefined,2));

const doCount = async () => {
  let count = await Character.count();

  if (count > 3)
    throw new Error("too many charaters");

  return count;

};


(async function() {

  try {
    const conn = await mongoose.connect(uri);

    await Promise.all(Object.entries(conn.models).map(([k,m]) => m.remove()))

    await Character.insertMany(
      ["Huey","Duey","Louie"].map(name => ({ name }))
    );

    let count = await doCount();
    log({ count });

    await Character.create({ name: 'Donald' });

    let newCount = await doCount();
    console.log("never get here");


  } catch(e) {
    console.error(e)
  } finally {
    mongoose.disconnect();
  }

})()

或使用标准then()catch()语法:

const { Schema } = mongoose = require('mongoose');

const uri = 'mongodb://localhost/test';

mongoose.set('debug', true);
mongoose.Promise = global.Promise;

const characterSchema = new Schema({
  name: String
});

const Character = mongoose.model('Character', characterSchema);

const log = data => console.log(JSON.stringify(data,undefined,2));

function doCount() {
  return Character.count()
    .then(count =>  {

      if (count > 3)
        throw new Error("too many charaters");

      return count;
    });

};


(function() {

  mongoose.connect(uri)
    .then(conn => Promise.all(
      Object.entries(conn.models).map(([k,m]) => m.remove())
    ))
    .then(() => Character.insertMany(
      ["Huey","Duey","Louie"].map(name => ({ name }))
    ))
    .then(() => doCount())
    .then(count => log({ count }))
    .then(() => Character.create({ name: 'Donald' }))
    .then(() => doCount())
    .then(() => console.log("never get here"))
    .catch(e => console.error(e))
    .then(() => mongoose.disconnect() );

})()

两个列表的输出都是一样的:

Mongoose: characters.remove({}, {})
Mongoose: characters.insertMany([ { _id: 5b0f66ec5580010efc5d0602, name: 'Huey', __v: 0 }, { _id: 5b0f66ec5580010efc5d0603, name: 'Duey', __v: 0 }, { _id: 5b0f66ec5580010efc5d0604, name: 'Louie', __v: 0 } ], {})
Mongoose: characters.count({}, {})
{
  "count": 3
}
Mongoose: characters.insertOne({ _id: ObjectId("5b0f66ec5580010efc5d0605"), name: 'Donald', __v: 0 })
Mongoose: characters.count({}, {})
Error: too many charaters
    at doCount (/home/projects/characters/index.js:20:11)
    at <anonymous>
    at process._tickCallback (internal/process/next_tick.js:188:7)

正如你所看到的那样,函数很高兴地返回count保持3或者不足的值,但是当count大于3时,它会抛出一个异常停止进一步执行因为"never get here"消息永远不会被记录。

因此不需要&#34;回调&#34;在这里你不会使用一个,除非你把它包装在一个Promise中,无论如何都可以做同样类型的错误处理。

但如果你有一个&#34;错误&#34;然后throw错误。这在承诺链中工作正常,但是回调&#34;不作为承诺返回的东西根本不是该链的一部分,永远不会被抓住#34;因此,当您不需要时,请不要使用回调。

只是为了踢,用Promise包装一个回调就像:

function doCount() {
  return new Promise((resolve,reject) =>
    Character.count().exec((err,count) => {

      if (count > 3)
        reject(new Error("too many charaters"));

      resolve(count);
    })
  );
};

但它注意到没有必要考虑到本机方法会返回一些你可以作为Promise解决的东西。