在node.js和async.js上使用async方法的控制流

Question

我正在尝试更改一个没有任何控制流的工作代码，以便在完成所有操作后进行多少更改。没有控制流程，这是不可能的。

要这样做，我正在尝试异步，但我在这里有点困惑。

旧代码：

public static populate(){
    // Read all files inside the populate folder.
    fs.readdir(__config.path.populate, function(err, files){
        if(err){
            consoleDev(err);
        }else{
            // For each file, get the data to populate stored in the file.
            _.each(files, function(file){
                _.each(require(__config.path.base + __config.path.populate + file), function(documents){
                    // The file name must be the same as the targeted model.
                    var Model = __Dao.getModel(file.split('.')[0]);// Filter the extension.

                    if(Model){
                        // For each data, try to add it if it does not exist in the DB.
                        Model.findOrCreate(documents, function(err, doc, created){
                            if(created){
                                consoleDev('The following document was created in the [' + Model.modelName + '] collection: ' + JSON.stringify(doc));
                            }
                        });
                    }else{
                        consoleDev('Unable to populate the file: ' + file + '. The model was not found.')
                    }
                });
            });
        }
    });
}

新代码：

public static populate(){
    // Read all files inside the populate folder.
    fs.readdir(__config.path.populate, function(err, files){
        if(err){
            consoleDev(err);
        }else{
            _.each(files, function(file){
                // Read all files in async mode with control flow.
                async.each(require(__config.path.base + __config.path.populate + file), function(documents, callback){
                    // The file name must be the same as the targeted model.
                    var Model = __Dao.getModel(file.split('.')[0]);// Filter the extension.

                    if(Model){
                        // For each data, try to add it if it does not exist in the DB.
                        Model.findOrCreate(documents, function(err, doc, created){
                            if(created){
                                consoleDev('The following document was created in the [' + Model.modelName + '] collection: ' + JSON.stringify(doc));
                                Populate._added++;
                            }else{
                                Populate._read++;
                            }
                            callback();
                        });
                    }else{
                        callback('Unable to populate the file: ' + file + '. The model was not found.')
                    }
                });
            }, function(err){
                if(err){
                    console.log(err);
                }
                consoleDev(Populate._added + ' documents were added. There are now ' + Populate._read + ' + ' + Populate._added + ' = ' + (Populate._read + Populate._added) + ' documents populated.');
            });
        }
    });
}

最后在控制台上没有显示任何内容，我在控制台上没有任何错误。该脚本仍然有效，并且之前添加了DB中不存在的文档。但我仍然没有留言说我添加了多少。

我试图改为async.each(files, function(file, callback){，但收到错误Error: Callback was already called.。

我在这里缺少什么？