功能裏面的javascript mysql

Question

當我運行這個函數時，它返回時返回null，因爲我在mysql查詢中有返回值，我該如何解決這個問題？

function CheckStorage(Host, Slots, SSLocation) { 
    connection.query("SELECT * FROM `machines` WHERE `shost` LIKE '" + Host + "' AND `location` LIKE '" + SSLocation + "' AND `slotsa` >= " + Slots + "", function(err, rows, fields) { 
     if(rows[0]) { 
      console.log(rows[0]["ip"]); 
      return rows[0]["ip"]; 
     } else { 
      return false; 
     } 
    }); 
} 

Answer 1

connection.query是一個異步函數，所以CheckStorage在connection.query完成之前返回。您需要將處理查詢結果的回調函數傳遞給CheckStorage，然後在查詢結束時調用該函數。

function CheckStorage(Host, Slots, SSLocation, callback) { 
    connection.query("SELECT * FROM `machines` WHERE `shost` LIKE '" + Host + "' AND `location` LIKE '" + SSLocation + "' AND `slotsa` >= " + Slots + "", function(err, rows, fields) { 
     if(rows[0]) { 
      console.log(rows[0]["ip"]); 
      if (typeof callback == "function") { 
       callback(rows[0]["ip"]); 
      } 
     } 
    }); 
}