NodeJS 生成器永远不会到达某一行？

Question

我正在使用 co 到运行一个生成器函数来执行一些数据的抓取和清理。但是，我在循环后从未到达代码的特定部分。这是我的代码的样子：

function*(){
  var url = "mongodb://" + config.host + ":" + config.port + "/" + config.db;
  var db = yield MongoClient.connect( url );
  for( var establishment in [ {"establishment_id": 16} ] ){
    var establishment_type = establishment.id;
    var response = yield getRestaurants( establishment_type );
    var restaurants = JSON.parse( response.body ).restaurants;
    // here we create our restaurants in "saveable" form
    var saveableRestaurants = [];
    for(var i = 0; i < restaurants.length; i++){
        var saveableRestaurant = restaurants[i].restaurant;
        saveableRestaurant._id = restaurants[i].restaurant.R.res_id;
        // Remove unwanted fields
        //... code removed for brevity ...
        // convert cuisine string into its appropriate id form
        var cuisines = saveableRestaurant.cuisines.split(",");
        var ids = [];
        for( var i = 0; i < cuisines.length; i++ ){
            console.log("LOOKING UP ID FOR ", cuisines[i]);
            var match = yield db.collection(CUI).findOne({"cuisine_name":cuisines[i].trim()});
            console.log("ID FOR ", cuisines[i], " IS", match.cuisine_id);
            ids.push( id );
        }
        // I NEVER REACH THIS LINE!!!!
        console.log( "ALL IDS ", ids );
    }
  }
  db.close();
}

我从未到达函数末尾的控制台语句

Answer 1

您正在打开数据库连接并尝试使用数据库连接进行操作，因此您可以尝试使用 async.each 并且在完成每个功能后您可以关闭连接，我看到这就是问题所在那里。

Answer 2

很可能存在您没有注意到的异步异常。你应该使用

function*() {
  var url = "mongodb://" + config.host + ":" + config.port + "/" + config.db;
  var db = yield MongoClient.connect( url );
  try {
    for (var establishment of [ {"establishment_id": 16} ]) {
      var establishment_type = establishment.id;
      var response = yield getRestaurants( establishment_type );
      var restaurants = JSON.parse( response.body ).restaurants;
      // here we create our restaurants in "saveable" form
      var saveableRestaurants = [];
      for (var i = 0; i < restaurants.length; i++) {
        var saveableRestaurant = restaurants[i].restaurant;
        saveableRestaurant._id = restaurants[i].restaurant.R.res_id;
        // Remove unwanted fields
        //... code removed for brevity ...
        // convert cuisine string into its appropriate id form
        var cuisines = saveableRestaurant.cuisines.split(",");
        var ids = [];
        for (var i = 0; i < cuisines.length; i++) {
          console.log("LOOKING UP ID FOR ", cuisines[i]);
          var match = yield db.collection(CUI).findOne({"cuisine_name":cuisines[i].trim()});
          console.log("ID FOR ", cuisines[i], " IS", match.cuisine_id);
          ids.push( id );
        }
        console.log( "ALL IDS ", ids );
      }
    }
  } finally {
    db.close();
  }
}

另外不要忘记在 co 返回的承诺上加上 .catch(e => console.error(e))。

Answer 3

在搜索 MongoDB 文档后，我找到了解决方案：

var matches = db.collection( CUI ).find({"cuisine_name" : { "$in" : cuisines }});
while( yield matches.hasNext() ){
  var match = yield matches.next();
  ids.push( match.cuisine_id );  
}

NodeJS 生成器永远不会到达某一行？

NodeJS generator never reaches a certain line?

javascript

generator

node.js

ecmascript-6

co