mysqli結果集顯示爲null

Question

我試圖使用mysqli來顯示數據，但它什麼也沒有顯示。

我的代碼有什麼問題？

PHP類：

/* the database object */ 
     private $_db; 

     public function __construct($db=NULL) 
     { 
      if(is_object($db)) 
      { 
       $this->_db = $db; 
      } 
      else 
      { 

       $this->_db = new mysqli(DB_HOST, DB_USER, DB_PASS, DB_NAME); 
      } 
     } 

     public function displayQuotes() 
     { 
      $sql = "SELECT cQuotes, vAuthor, cArabic, vReference 
          FROM thquotes 
          ORDER BY RAND() 
         LIMIT 1;"; 



         $query = $this->_db->prepare($sql); 
         $query->execute(); 
        $query->store_result(); 

         /* bind variables to prepared statement */ 
         $query->bind_result($cQuotes, $vAuthor, $cArabic, $vReference); 


         if(!$query->num_rows==0) 
         { 
         while($row = $query->fetch()) 
         { 
          //echo $this->formatQuotes($row); 
          $formatHTML = new formatHTML(); 
          echo $formatHTML->formatQuotes($row); 
         } 


         } 
         else 
         { 
          echo "There are no Quotes!"; 
         } 
         $query->free_result(); 
         $query->close(); 



     } 

它讀取的if(!$query->num_rows==0)和數據的語句是有在結果，因爲它並沒有去別的一部分，但我想不通爲什麼它不顯示任何內容。

php文件：

include "base.php"; 
include_once "inc/class.quotes-m.inc.php"; 
$quotes = new Quotes($db); 

$quotes->displayQuotes(); 

PHP base.php：

include_once("inc/constants.inc.php"); 

error_reporting(E_ALL); 
ini_set("display_errors", 1); 



     $db = new mysqli(DB_HOST, DB_USER, DB_PASS, DB_NAME); 

     if (!$db) { 
      echo 'db link fail'; 
     } 

Answer 1

！具有比higher precedence ==，即

if(!$query->num_rows==0) { ... } 
// is equivalent to 
if((!$query->num_rows) == 0) { ... } 

即$query->num_rows邏輯否定（涉及一個內部 - >布爾鑄造），那麼這布爾值與0。

但是你要像

if(0 < $query->num_rows) { ... } 

---

你使用try {...} catch（）塊。但mysqli extension不會拋出異常（IIRC）。除非$this->_db是某種（附加）包裝器，否則您必須測試mysqli方法的返回值，或者使用實際在發生錯誤（例如，錯誤）時引發異常的api。 PDO（將錯誤模式設置爲PDO :: ERRMODE_EXCEPTION時）。

---

public function displayQuotes() 
    { 
    $sql = " 
     SELECT cQuotes, vAuthor, cArabic, vReference 
     FROM thquotes 
     ORDER BY RAND() 
     LIMIT 1 
    "; 

    $query = $this->_db->prepare($sql); 
    if (!$query) { 
     throw new ErrorException($this->_db->error, $this->_db->errno); 
    } 
    $r = $query->execute(); 
    if (!$r) { 
     throw new ErrorException($query->error, $query->errno); 
    } 

    $r = $query->store_result(); 
    if (!$r) { 
     throw new ErrorException($query->error, $query->errno); 
    } 

    /* bind variables to prepared statement */ 
    $r = $query->bind_result($cQuotes, $vAuthor, $cArabic, $vReference); 
    if (!$r) { 
     throw new ErrorException($query->error, $query->errno); 
    } 

    if(0 < $query->num_rows) { 
     $formatHTML = new formatHTML(); 
     while(false!==($row=$query->fetch())) { 
     echo $formatHTML->formatQuotes($row); 
     } 
    } 
    else { 
     echo "There are no Quotes!"; 
    } 
    $query->free_result(); 
    $query->close(); 
    }