上传多个文件时出现异步问题

Question

您好我正在尝试上传多个文件，文件写入是正确的。但我想将文件移动到 mongo 网格 fs 中，第一个文件只是正确移动文件的其余部分没有移动到网格 fs 中，也没有取消链接。

这是我的代码：

for (var i = 0; i < files.length; i++) {
    (function(i) {
        var singleFile = files[i];
        var fileData = JSON.parse(files[i].name);
        var fileName = fileData.fileName;
        var fileType = files[i].type;
        var uniqId = fileData.attachmentId;
        var targetPath = "./attachments/" + uniqId;
        var tmp_path = files[i].path;

    console.log("uniqId : " + uniqId);
    //uploadFile(tmp_path,targetPath,fileName,uniqId,fileType);

    fs.readFile(tmp_path, function(err, data) {
        fs.writeFile(targetPath, data, function(err) {
            if (!err) {
                mongoose.connect(configSettings.mongodb.ip, configSettings.mongodb.databasename, configSettings.mongodb.port, function(err, succ) {
                    var id = new ObjectID(uniqId);
                    new GridStore(mongoose.connection.db, id, fileName, 'w', {
                        'content_type': 'application/octet-stream'
                    }).open(function(err, gs) {
                        gs.writeFile(targetPath, function(err) {
                            if (err) {
                                console.log("err");
                            }
                            gs.close(function(err) {
                                console.log("success");
                                fs.unlink("./attachments/" + uniqId, function(err) {
                                    console.log("err : " + err);
                                    console.log(uniqId + ' ::successfully deleted ');
                                });
                                mongoose.connection.close();
                            });
                        });
                    });
                });
            }
        });
    });
   })(i);
}

    res.send("success");

我尝试过使用闭包函数，即使我也尝试过创建单独的函数，但结果相同（仅插入和取消链接一个文件）。

在这种情况下，我必须做什么才能将所有文件存储在 gridfs 中并从临时文件夹中取消链接？

Answer 1

这是我的猜测。由于您的调用被推迟到以后，您的函数结束并且文件列表可能被 Node 或其他任何东西删除，您可以在这里看到一个简化的示例：

let myList = [1, 2, 3, 4, 5];

function doWork(list) {
  console.log('Start of function');
  
  for (let i = 0; i < list.length; i++) {
    (function(i) {
      setTimeout(function() {
        console.log('Working on index', i);
        console.log('list[i] :', list[i]);
      }, 100);
    })(i);
  }

  console.log('End of function');
}

doWork(myList);

myList[4] = null;

解决方案是将文件（或列表/索引对）本身包含在您的上下文中以使其保持活动状态：

let myList = [1, 2, 3, 4, 5];

function doWork(list) {
  console.log('Start of function');
  
  for (let i = 0; i < list.length; i++) {
    (function(num) {
      setTimeout(function() {
        console.log('Num :', num);
      }, 100);
    })(list[i]);
  }

  console.log('End of function');
}

doWork(myList);

myList[4] = null;

Answer 2

实际上问题出在 gridFs 连接上，文件在循环内上传，网格连接已启动并写入第一个文件，循环继续并行。一旦从gridfs打开连接，它应该在插入另一个文件之前关闭，并且必须正确重新连接下一次。

这是工作代码检查它：

var files = req.files.fileData[0];
var count = "";

if(files instanceof Array){
    count = files.length;
}
else{
    count = 1;
}

if(!fs.existsSync('./attachments')){
    console.log("Creating the attachments folder.");
    fs.mkdir('./attachments');
}   

function moveToGrid(gridArr,callback){      
    var uniqId = gridArr.uniqId, 
        filePath = gridArr.targetPath, 
        fileName = gridArr.fileName,
        fileType = gridArr.fileType;

        console.log(filePath+' '+fileName+' '+fileType + ' '+uniqId);

    mongoose.connect(configSettings.mongodb.ip, configSettings.mongodb.databasename, configSettings.mongodb.port, function (err, succ){

        var uploadResponse   = function(uniqId){
            // Delete the tmp file
            fs.unlink("./attachments/" + uniqId, function (err) {
                console.log(uniqId + ' ::temp file successfully deleted ');
            });
             mongoose.connection.close();
             console.log("=========request END time==========::::" + (new Date()).toString() + "::" +(new Date()).getMilliseconds() );
             callback();
        };
        var id = new ObjectID(uniqId);
        new GridStore(mongoose.connection.db,id,fileName, 'w',{'content_type':'application/octet-stream'}).open(function(err, gs) {
            gs.writeFile(filePath, function(err) {
                if(err){
                console.log("err : "+err);
                }
                gs.close(function(err) {
                    uploadResponse(uniqId);
                });
            });
        });
    });
}

var recursive = function(gridArr){  
    function uploader(i){
      if( i < gridArr.length ){
        moveToGrid(gridArr[i],
             function(){
              uploader(i+1)
             });
       }
       else{
        res.send("success");
       }
    }
    uploader(0); 
}

if(count > 1){
    var gridArr = [];
    for(var i=0; i<files.length; i++){
        (function(i){
            var singleFile = files[i];
                var fileData = JSON.parse(singleFile.name);
                var fileName = fileData.fileName;
                var fileType = singleFile.type;
                var uniqId   =  fileData.attachmentId;
                var targetPath =  "./attachments/" + uniqId;
                var tmp_path = singleFile.path;

                fs.readFile(tmp_path,function(err,data){
                    fs.writeFile(targetPath,data,function(err){
                        if(!err){
                            gridArr.push({"uniqId":uniqId, "targetPath":targetPath, "fileName":fileName, "fileType":fileType});
                            count --;
                            if(count == 0){
                                recursive(gridArr);
                            }
                        }
                    });
                });
        }(i));                  
    }
}
else{
    var gridArr = [];
    var singleFile = files;
    var fileData = JSON.parse(singleFile.name);
    var fileName = fileData.fileName;
    var fileType = singleFile.type;
    var uniqId   =  fileData.attachmentId;
    var targetPath =  "./attachments/" + uniqId;
    var tmp_path = singleFile.path;

    fs.readFile(tmp_path,function(err,data){
        fs.writeFile(targetPath,data,function(err){
            if(!err){
                gridArr.push({"uniqId":uniqId, "targetPath":targetPath, "fileName":fileName, "fileType":fileType});
                count --;
                if(count == 0){
                    recursive(gridArr);
                }
            }
        });
    });     
}

使用此代码，我们可以将多个文件插入到 mongo gridFs.. 希望这会有所帮助！

Answer 3

简短的回答在这里学习如何在循环中异步函数

(function loop(i) {
if(i==4) return
setTimeout(function() {
  console.log('Working on index', i);
  loop(++i)
 }, 1000);
})(0);

TL;DR https://mongodb.github.io/node-mongodb-native/api-generated/gridstore.html