php - 在 OOP php 中获取查询错误

Question

我只是 OOP php 的新手，我很难弄清楚如何使用类方法在数据库中进行查询。这是我的代码，我遇到了一个我不知道如何解决的错误。

我声明了连接变量，但我不知道为什么它是未定义的

Notice: Undefined variable: connection

Fatal error: Call to a member function query() on a non-object in

db.php

class DbConnector {

   private $serverName;
   private $userName;
   private $password;
   private $dbName;
   private $connection;

   public function __construct(){
      $this->serverName = "localhost";
      $this->userName = "root";
      $this->password = "attl";
      $this->dbName = "oop";

      $this->connection = new mysqli($this->serverName, $this->userName, $this->password, $this->dbName);

      if ($this->connection->connect_error) {
          $this->connection = die("Connection failed: " . $this->connection->connect_error);
      } 
  }

  public function getConnection(){
      return $this->connection;
  }
}

索引.php

include('../queries/db.php');

class Users{

  private $connection;

  public function __construct(){
      $con = new DbConnector();
      $connection = $con->getConnection();
  }
  public function getUsers(){
      $sql = $connection->query("SELECT * FROM login");

      while($getUsers = $sql->fetch_array()){
          echo $getUsers['username'];
      }
  }

}

$user = new Users();
return $user->getUsers();

Answer 1

您的问题是您试图访问局部范围的变量而不是类属性

public function getUsers(){
  $sql = $connection->query("SELECT * FROM login"); // HERE

  while($getUsers = $sql->fetch_array()){
      echo $getUsers['username'];
  }
}

这在该范围内找不到名为 $connection 的变量，您需要使用 $this 访问对象属性。

class Users {

  private $connection;

  public function __construct()
  {
      $con = new DbConnector();
      // Assign this to object propety declared above 
      $this->connection = $con->getConnection();
  }

  public function getUsers()
  {
      // now access the object property set in constructor.
      $sql = $this->connection->query("SELECT * FROM login");

      while($getUsers = $sql->fetch_array()){
          echo $getUsers['username'];
      }
  }
}