无法从函数返回

时间：2019-06-07 16:46:02

标签： mysql node.js discord.js

所以我想做的是创建一个函数，使用mysql（不在乎如何，但是我找到了一个npm，所以现在就使用它。）从数据库中获取信息，然后提供我的json用它。只要console.log（）在正确的位置，它就可以正常工作，但是我必须返回它，所以我必须将其进一步向下移动。但是当我这样做时，它将不会显示在我需要的其他文件中。

我有两个基本相同的剧本，一个只适合另一个派别。 -所以我只会显示一个，就好像我为其中一个找到了解决方案一样，我对两个都有解决方案。

get_ally_online_players: function (guild) {

  con.query("SELECT * FROM user_dbs WHERE guild='"+ guild +"'", function (err, result, fields) {

    var con2 = mysql.createConnection({
        host: result[0].host,
        user: result[0].username,
        password: result[0].password,
        database: result[0].database
    })


    con2.connect()

    con2.query("SELECT * FROM characters WHERE online='1' AND race=1 OR race=3 OR race=4 OR race=7 OR race=11", function (err, result, fields) {
      allycount = 0
      console.dir(result)
      result.forEach(function(result) {
        allycount = allycount+1
      })
      return allycount

    });
    con2.end()
  });
}

在这里我尝试拥有它：

        if(recieved.content === "!status")
        {

            var horde_players
            var ally_players
            horde_players == guilddb.get_horde_online_players("585919060722712670")
            ally_players == guilddb.get_ally_online_players("585919060722712670")
            console.log(guilddb.test())
            //console.log(ally_players)
            recieved.channel.send(ally_players + " : " + horde_players)
        }

我已经尝试了很多事情...我还读到您必须使用回调函数，因为它显然太快了，就像以前无法查询一样... 不过，我想远离回调，因为在脚本中包含它似乎很麻烦。但是，如果绝对必要，那就这样吧。它返回“未定义” btw。我也曾尝试使用Promise并放置setTimeout函数等。

2 个答案:

答案 0 :(得分：1)

首先，对我的英语感到抱歉。

实际上您犯了一些错误。

您在犯错误的情况下将值分配给 horde_players 和 ally_players 值

<div class="searching-result" data-id="somehashvalue" abc="xyz"></div>

使用（==），您正在比较值，而不是设置。

现在让我们讨论异步操作。

我准备了一个例子。就像您的情况一样，您试图运行两个可能在不同时间完成的异步操作，但是在运行其他操作之前您需要将它们都完成。尝试运行它：

if (recieved.content === "!status") {
    var horde_players
    var ally_players
    horde_players = guilddb.get_horde_online_players("585919060722712670")
    ally_players = guilddb.get_ally_online_players("585919060722712670")
    console.log(guilddb.test())
    //console.log(ally_players)
    recieved.channel.send(ally_players + " : " + horde_players)
}

完成的结果是在完成两个异步操作之前运行的。错误...

使用回调，我们需要嵌套函数（如果您必须执行更多异步操作，则可能会导致回调地狱）

function async1(id, callback) {
    setTimeout(function() {
        callback('The user with ' + id + ' is called Sergio');
    }, 6000);
}

function async2(id, callback) {
    setTimeout(function() {
        callback('The user with ' + id + ' is called Jack');
    }, 2000);
}

var result1;
var result2;

async1(1, function(result) {
    result1 = result;
});

async2(2, function(result) {
    result2 = result;
});
console.log('Finished result: ' + result1 + result2); // Finished result: undefined undefined

对于您而言，这就是我的解决方案。也许我会改善更多的功能，例如使用const-let和ES6功能（异步等待，箭头功能...），传递数据库连接器引发的参数崩溃……但也许现在更容易理解

function async1(id, callback) {
    setTimeout(function() {
        callback('The user with ' + id + ' is called Sergio');
    }, 6000);
}

function async2(id, callback) {
    setTimeout(function() {
        callback('The user with ' + id + ' is called Jack');
    }, 2000);
}

var result1;
var result2;

async1(1, function(result) {
    result1 = result;

    async2(2, function(result) {
        result2 = result;
        console.log('Finished result: ' + result1 + result2); // 'Finished result: The user with 1 is called SergioThe user with 2 is called Jack
    });
});

希望有帮助。

答案 1 :(得分：0)

您的查询是异步的，因此该函数将在查询完成之前隐式返回 undefined 。

因此，您将需要使用回调或Promise。

您可以使用如下回调：

 public class Kompjuterike extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_kompjuterike);

    displayUpload();
    editPdfName = (EditText) findViewById(R.id.txtuploadfile);
    pdfupload = (ImageView) findViewById(R.id.pdfuploadimg);
    imgupload = (ImageView) findViewById(R.id.imguploadimg);
    storageReference = FirebaseStorage.getInstance().getReference();
    databaseReference = 
    FirebaseDatabase.getInstance().getReference(databasepath);



}
private void selectPDFFile() {
    Intent intent=new Intent();
    intent.setType("application/pdf");
    intent.setAction(Intent.ACTION_GET_CONTENT);
    startActivityForResult(Intent.createChooser(intent,"select pdf file"),1);
}

private void selectIMGFile() {
    Intent intent=new Intent();
    intent.setType("image/*");
    intent.setAction(Intent.ACTION_GET_CONTENT);
    startActivityForResult(Intent.createChooser(intent,"select img file"),1);
}

@Override
protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if(requestCode==1 && resultCode==RESULT_OK && data!=null && data.getData()!=null){
        uploadFile(data.getData());
    }
}


private void uploadFile(Uri data) {
    final ProgressDialog progressDialog=new ProgressDialog(this);
    progressDialog.setTitle("Uploading file...");
    progressDialog.show();
    final  StorageReference reference=storageReference.child(databasepath+"/"+System.currentTimeMillis());
    reference.putFile(data).addOnSuccessListener(new OnSuccessListener<UploadTask.TaskSnapshot>() {
        @Override
        public void onSuccess(UploadTask.TaskSnapshot taskSnapshot) {

            Toast.makeText(Kompjuterike.this, "Upload successful!", Toast.LENGTH_LONG).show();
            reference.getDownloadUrl().addOnSuccessListener(new OnSuccessListener<Uri>() {
                @Override
                public void onSuccess(Uri uri) {
                    String url = uri.toString();
                    Upload upload = new Upload(editPdfName.getText().toString(), url);
                    String uploadId = databaseReference.push().getKey();
                    databaseReference.child(uploadId).setValue(upload);
                    Toast.makeText(Kompjuterike.this, "File Uploaded", Toast.LENGTH_SHORT).show();
                    progressDialog.dismiss();
                }
            });

        }
    }).addOnProgressListener(new OnProgressListener<UploadTask.TaskSnapshot>() {
        @Override
        public void onProgress(UploadTask.TaskSnapshot taskSnapshot) {
            double progress=(100.0*taskSnapshot.getBytesTransferred())/taskSnapshot.getTotalByteCount();
            progressDialog.setMessage("Uploaded: "+(int)progress+"%");

        }
    });
}

private void displayUpload(){
    uploadList = new ArrayList<>();
   listView = (ListView) findViewById(R.id.listView1);


    //adding a clicklistener on listview
    listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
            //getting the upload
            Upload upload = uploadList.get(i);

            //Opening the upload file in browser using the upload url
            Intent intent = new Intent(Intent.ACTION_VIEW);
            intent.setData(Uri.parse(upload.getUrl()));
            startActivity(intent);
        }
    });

    //getting the database reference
    databaseReference = FirebaseDatabase.getInstance().getReference(databasepath);


    //retrieving upload data from firebase database
    databaseReference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for (DataSnapshot postSnapshot : dataSnapshot.getChildren()) {
                Upload upload = postSnapshot.getValue(Upload.class);
                uploadList.add(upload);
            }

            String[] uploads = new String[uploadList.size()];

            for (int i = 0; i < uploads.length; i++) {
                uploads[i] = uploadList.get(i).getName();
            }

            //displaying it to list
          adapter = new ArrayAdapter<String>(getApplicationContext(), R.layout.listview_color,R.id.list_content, uploads);

            listView.setAdapter(adapter);

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });
}

...然后将回调函数传递给// Accept a callback function as an argument get_ally_online_players: function (guild, callback) { con.query("SELECT * FROM user_dbs WHERE guild='"+ guild +"'", function (err, result, fields) { var con2 = mysql.createConnection({ host: result[0].host, user: result[0].username, password: result[0].password, database: result[0].database }) con2.connect() con2.query("SELECT * FROM characters WHERE online='1' AND race=1 OR race=3 OR race=4 OR race=7 OR race=11", function (err, result, fields) { allycount = 0 console.dir(result) result.forEach(function(result) { allycount = allycount+1 }) // Pass the result to the callback function callback(allycount) }) con2.end() }) } ，该回调函数将在准备就绪时接收数据：

get_ally_online_players

我希望这会有所帮助。

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