執行幾個貓鼬查詢：如何使用promise來代替？

Question

我有下面的代碼，我想避免嵌套的回調：

app.get '/performers', (req, res) -> 
    conductor = require('models/conductor').init().model 
    soloist = require('models/soloist').init().model 
    orchestra = require('models/orchestra').init().model 
    chamber = require('models/chamber').init().model 
    performers = {} 
    conductor.find {}, (err, result) -> 
     performers.conductor = result 
     soloist.find {}, (err, result) -> 
      performers.soloist = result 
      orchestra.find {}, (err, result) -> 
       performers.orchestra = result 
       chamber.find {}, (err, result) -> 
        performers.chamber = result 
        res.json performers 

任何想法？

Answer 1

我發現async庫是一個更清潔的解決方案，比承諾這種事情。對於這種特定情況，async.parallel會運行良好。

我不是太熟悉的CoffeeScript，但它會是這個樣子：

performers = {} 
async.parallel [ 
    (callback) -> 
     conductor.find {}, (err, result) -> 
      performers.conductor = result 
      callback err 
    (callback) -> 
     soloist.find {}, (err, result) -> 
      performers.soloist = result 
      callback err 
    (callback) -> 
     orchestra.find {}, (err, result) -> 
      performers.orchestra = result 
      callback err 
    (callback) -> 
     chamber.find {}, (err, result) -> 
      performers.chamber = result 
      callback err 
    ], (err) -> 
     res.json performers 

Answer 2

您也可以組織這樣的代碼：

exports.index = function(req, res){ 
    var _self = {}; 

    var foundItems = function(err, items){ 
     _self.items = items; 
     res.render('index', { user: _self.user, items: _self.items, lists: _self.lists }); 
    }; 

    var foundLists = function(err, lists){ 
     _self.lists = lists; 
     Items.find().exec(foundItems); 
    }; 

    var foundUser = function(err, user){ 
     _self.user = user; 
     List.find().exec(foundLists); 
    }; 

    User.findById(user).exec(foundUser); 
};