NodeJS 异步和递归

Question

我进行了广泛的搜索，但找不到似乎可行的答案。我试过 Q.deferred、async.series、async.each，我似乎无法让这个笨蛋工作：

这是代码，它可以工作，但是，"return subTree" 在递归完成之前触发 "tree" 导出。我已经验证递归正在适当地挖掘。我真的需要 recuriveChildren 上的 return 来等待递归调用完成。

exports.tree = function(req, res) {
 var tree = {
  'name': 'New Account'
 };

 var methods = {};

 methods.recursiveChildren = function(path) {
  var subTree = {
   'name': path.field.label+":"+path.match+":"+path.value,
   'id': path._id,
   'parent': path.parent,
   'children': []
  }
  
  Path.find({parent:path._id}).sort({date_created:1}).exec(function (err,childpaths) {
   
   for ( var z in childpaths ) {
    var tmpTree = methods.recursiveChildren(childpaths[z]);
    subTree.children.push(tmpTree);
   }
   
  });
  
  return subTree;
  
 }


 Path.find({parent:null}).sort({date_created:1}).exec(function (err,paths) {
  tree.children = [];
  for ( var x in paths ) {

   var tmpTree = methods.recursiveChildren(paths[x]);
   tree.children.push(tmpTree);
  }

  res.jsonp(tree);
 });
 
};

Answer 1

关于异步模式的令人困惑的事情是你不能 return 实际值，因为那还没有发生。您可以传入异步操作完成后要执行的函数（回调），或者您可以 return 一个接受回调（承诺）的对象，一旦操作解决了承诺，该对象就会执行回调一个值。

exports.tree = function(req, res) {
  var tree = {
    'name': 'New Account'
  };

  var methods = {};

  methods.recursiveChildren = function(path) {
    var subTree = {
      'name': path.field.label + ":" + path.match + ":" + path.value,
      'id': path._id,
      'parent': path.parent,
      'children': []
    }

    return new Promise(function(resolve, reject) {
      Path.find({
        parent: path._id
      }).sort({
        date_created: 1
      }).exec(function(err, childpaths) {

        Promise
          .all(childpaths.map(function(childpath) {
            /* collect a promise for each child path this returns a promise */
            return methods.recursiveChildren(childpath);
          }))
          .then(function(resolvedPaths) {
            subtree.children = resolvedPaths;
          
             /* the top level promise is fulfilled with the subtree */
            resolve(subTree);
          });
      });
    });
  }


  Path.find({
    parent: null
  }).sort({
    date_created: 1
  }).exec(function(err, paths) {
    Promise.all(paths.map(function(path) {
      return methods.recursiveChildren(path);
    })).then(function(resolvedPaths) {
      tree.paths = resolvedPaths;
      res.jsonp(tree);
    });
  });

};

NodeJS 异步和递归

NodeJS Asynchronous and Recursive

node.js

asynchronous

recursion

deferred