PHP MySQLi num_rows 总是返回 0

Question

我构建了一个类，它利用了 PHP 的内置 MySQLi 类的功能，旨在简化数据库交互。但是，使用 OOP 方法时，我很难使用 num_rows 实例变量在运行查询后返回正确的行数。看看我类(class)的快照......

class Database {
//Connect to the database, all goes well ...

//Run a basic query on the database
  public function query($query) {
  //Run a query on the database an make sure is executed successfully
    try {
    //$this->connection->query uses MySQLi's built-in query method, not this one
      if ($result = $this->connection->query($query, MYSQLI_USE_RESULT)) {
        return $result;
      } else {
        $error = debug_backtrace();
            
        throw new Exception(/* A long error message is thrown here */);
      }
    } catch (Exception $e) {
      $this->connection->close();
        
      die($e->getMessage());
    }
  }

//More methods, nothing of interest ...
}

这是一个示例用法:

$db = new Database();
$result = $db->query("SELECT * FROM `pages`"); //Contains at least one entry
echo $result->num_rows; //Returns "0"
exit;

这怎么不准确？结果对象的其他值是准确的，例如“field_count”。

Answer 1

可能的错误:http://www.php.net/manual/en/mysqli-result.num-rows.php#104630

代码来自上面的源代码 (Johan Abildskov):

$sql = "valid select statement that yields results"; 
if($result = mysqli-connection->query($sql, MYSQLI_USE_RESULT)) 
{ 
          echo $result->num_rows; //zero 
          while($row = $result->fetch_row()) 
        { 
          echo $result->num_rows; //incrementing by one each time 
        } 
          echo $result->num_rows; // Finally the total count 
}

也可以使用程序风格进行验证:

/* determine number of rows result set */
$row_cnt = mysqli_num_rows($result);