我正在尝试设置类，但继续在第41行获取错误“num_rows行”，错误是“试图获取第41行中非对象的属性”

Question

<?
class Db {
  private $connection;
  public  function __construct($option = null){
    if  ($option != null){
      $host  = $option['host'];
      $user  = $option['user'];
      $pass  = $option['pass'];
      $name  = $option['name'];

    }else {

      global $config;
      $host = $config['db']['host'];
      $user = $config['db']['user'];
      $pass = $config['db']['pass'];
 $name = $config['db']['name'];
 }
    $this->connection = new mysqli($host, $user, $pass, $name);
    if ($this->connection()->connect_error){
      echo("Connection failed: " .$this->connection->connect_error);
      exit;
    }

    $this->connection->query("SET NAMES ''utf8");
  }
  public function first($sql) {
   $records = $this->query($sql);
    if ($records == null){
      return null;
    }
    return $records[0];
  }

  public function  query($sql){
    $result = $this->connection->query($sql);
    $records = array();

     if ($result->num_rows == 0) {
        return null;
      }
      while ($row = $result->fetch_assoc()) {
        $records[] = $row;
      }
    return $records;
  }
  public function connection(){
    return $this->connection;
  }
  public function close(){
    $this->connection()->close();
  }
}

Answer 1

The return type of the mysqli::query function is mixed so it depends on the $sql query you are sending.

If the query is something like "CREATE TABLE myTable like anotherTable;" the return of the query is either TRUE or FALSE. On the other hand if it is really a SELECT query, if the operation is not successful you should expect FALSE otherwise you have a $result object.

so it is better check the type of $result before performing operations. I suggest add some checking in your codes like follows:

public function  query($sql){
    $result = $this->connection->query($sql);
    $records = array();
    if($result === FALSE)
       return FALSE;

    if ($result->num_rows == 0) {
       return null;
    ....
}