蔚藍的異步JavaScript後端 - 等待函數

Question

我正在使用Azure移動服務和一個JavaScript後端。我的問題是該函數不會等待其他函數的結束。

我試圖選擇一個具有特殊規則的項目（單詞）。我想選擇item.wordnumber最高的項目。如果有少量項目具有相同的item.wordnumber，我想選擇與該項目相關的投票的最高票數（在另一個表中爲「投票」）。

此腳本不會等待函數CalcolateMaxAvg的返回。 我會盡我所能在C＃中等待。

var tableWords = tables.getTable('Word'); 
var tableVotes = tables.getTable('Votes'); 

var avgVotesActualWord = 0; 
var maxItem = null; 
var maxItemVote = 0; 


function WordChoice() { 

var select = tableWords.orderByDescending('wordnumber').read({success: 
     function (results) 
     { 
      results.forEach(function(item) 
      { 
       if(maxItem == null) 
       { 
        maxItem = item; 
        maxItemVote = tableVotes.where({idword: item.id}).read({success: CalcolateMaxAvg}); 
       } 
       else if(item.wordnumber > maxItem.wordnumber) 
       { 
        maxItem = item; 
        maxItemVote = tableVotes.where({idword: item.id}).read({success: CalcolateMaxAvg}); 
       } 
       else if(item.wordnumber == maxItem.wordnumber) 
       { 
        //chack who have more votes 
        avgVotesActualWord = 0; 
        avgVotesActualWord = tableVotes.where({idword: item.id}).read({success: CalcolateMaxAvg}); 

        //the problem is avgVoteActualWord that is always NaN 
        console.log('Word: %s with avg: %d', item.word, avgVotesActualWord); 

        if(avgVotesActualWord > maxItemVote) 
        { 
         //take the actualword because have more votes 
         maxItem = item; 
         maxItemVote = avgVotesActualWord; 
        } 
       } 
      }) 

      if(maxItem != null) 
      { 
       console.log('parola: %s', maxItem.word); 
       maxItem.selected = true; 
       tableWords.update(maxItem); 
      } 
      else 
      { 
       console.log('null'); 
      } 
     } 
    }); 
} 


function CalcolateMaxAvg(resultsVote) 
{ 

    var sum = 0; 
    var count = 0; 
    var avg = 0; 
    resultsVote.forEach(function(itemVote) 
    { 
     sum = sum + itemVote.vote; 
     count = count + 1; 
    }) 
    if(count > 0) 
    { 
     avg = sum/count; 
    } 

    //this is a correct value of avgVoteActualWord, but he don't wait the return of this value 
    console.log('avg: %d', avg); 

    return avg; 
} 

Answer 1

的問題是，要table.where(...).read(...)調用是異步 - 它不會返回由CalcolateMaxAvg功能（它不會返回任何東西）返回一個數字。您需要重寫您的代碼以涵蓋JavaScript的異步性，這些內容與下面的代碼一致。

var tableWords = tables.getTable('Word'); 
var tableVotes = tables.getTable('Votes'); 

var avgVotesActualWord = 0; 
var maxItem = null; 
var maxItemVote = 0; 

function WordChoice() { 

    var select = tableWords.orderByDescending('wordnumber').read({ 
     success: function (results) 
     { 
      function processNextResult(index) { 
       if (index >= results.length) { 
        // All done 

        if(maxItem != null) 
        { 
         console.log('parola: %s', maxItem.word); 
         maxItem.selected = true; 
         tableWords.update(maxItem); 
        } 
        else 
        { 
         console.log('null'); 
        } 

        return; 
       } 

       var item = results[index]; 
       if (maxItem == null) { 
        maxItem = item; 
        tableVotes.where({ idword: item.id }).read({ success: simpleProcessVotesResult }); 
       } else if (item.wordnumber > maxItem.wordnumber) { 
        maxItem = item; 
        tableVotes.where({ idword: item.id }).read({ success: simpleProcessVotesResult }); 
       } else if (item.wordnumber == maxItem.wordnumber) { 
        //check who have more votes 
        avgVotesActualWord = 0; 
        tableVotes.where({idword: item.id}).read({ 
         success: function(resultsVote) { 
          avgVotesActualWord = CalcolateMaxAvg(resultsVote); 
          //the problem is avgVoteActualWord that is always NaN 
          console.log('Word: %s with avg: %d', item.word, avgVotesActualWord); 

          if(avgVotesActualWord > maxItemVote) 
          { 
           //take the actualword because have more votes 
           maxItem = item; 
           maxItemVote = avgVotesActualWord; 
          } 

          processNextResult(index + 1); 
         } 
        }); 
       } else { 
        processNextResult(intex + 1); 
       } 
      } 

      function simpleProcessVotesResult(resultsVote) { 
       maxItemsVote = CalcolateMaxAvg(resultsVote); 
       processNextResult(intex + 1); 
      } 
      processNextResult(0); 
     } 
    }); 
} 

function CalcolateMaxAvg(resultsVote) 
{ 

    var sum = 0; 
    var count = 0; 
    var avg = 0; 
    resultsVote.forEach(function(itemVote) 
    { 
     sum = sum + itemVote.vote; 
     count = count + 1; 
    }) 
    if(count > 0) 
    { 
     avg = sum/count; 
    } 

    //this is a correct value of avgVoteActualWord, but he don't wait the return of this value 
    console.log('avg: %d', avg); 

    return avg; 
}