Node.js的 - 裏面的foreach

Question

MySQL查詢我的代碼，這樣的結構：

connection.query(query1,function(err,rows) { 
    var response = []; 
    //doing something with rows 
    rows.forEach(function(item) { 
     connection.query(queryItem,function(err,rows) { 
      //doing something 
      result = rows[0].field; 
      //and want to push it to an array 
      response.push(result); 
     }); 
    }); 
    console.log(response); //empty 
}); 

我知道的forEach阻止，但查詢是非阻塞。我試圖用承諾：

connection.query(query1,function(err,rows) { 
    var response = []; 
    //doing something with rows 
    rows.forEach(function(item) { 
     var promise = new Promise(function(resolve,reject) { 
      connection.query(queryItem,function(err,rows) { 
       //doing something 
       result = rows[0].field; 
       //and want to push it to an array 
       resolve(result); 
      }); 
     }); 
     promise.then(function(result) { 
      console.log(result); //ok 
      response.push(result) //not ok, result is empty 
     }); 
    }); 
    console.log(response); //empty 
}); 

但它沒有幫助。我如何從非阻塞函數中將值推入數組並在之後使用它？

Answer 1

創建承諾是朝着正確方向邁出的一步，但您需要進一步將承諾彙總到數組並傳遞給Promise.all，然後等待它們全部完成，然後嘗試訪問response 。

connection.query(query1,function(err,rows) { 
    var response = []; 
    //doing something with rows 
    Promise.all(rows.map(function(item) { 
     var promise = new Promise(function(resolve,reject) { 
      connection.query(queryItem,function(err,rows) { 
       //doing something 
       result = rows[0].field; 
       //and want to push it to an array 
       resolve(result); 
      }); 
     }); 
     return promise.then(function(result) { 
      console.log(result); //ok 
      response.push(result) //ok 
     }); 
    }).then(function() { 
     console.log(response); //not empty 
    }); 
});