PHP致命错误：调用成员函数prepare（）

Question

class DBconnection {

    protected $connection;

    public function __construct(){
        $this->dbConnect();
    }

    public function dbConnect() {
        try {

            // Try and connect to the database, if a connection has not been established yet{
            // Load configuration as an array. Use the actual location of your configuration file
            $config = parse_ini_file("config.ini"); 
            $dsn = 'mysql:host='. $config['host'] .';dbname=' . $config['dbname'] . ';charset=utf8;';
            $this->connection = new PDO($dsn, $config['username'], $config['password']);

            //echo 'Connection to database has been successfull!';
            return $this->connection;

        } catch(Exception $e) {
            echo 'There was an error while connecting to the database!';
            $this->connection = NULL;
        }
    }

    public function disConnect(){
        $this->connection = NULL;
        //echo '<br>Database connection has been disconnected successfully!';
    }
}

class DBTransaction extends DBconnection {

    public function __construct(){
        parent::__construct();
    }

    // FETCH ALL DATA
    public function select_all($query) {
      try {
            $result = $this->connection->query($query);
                $result->execute();
                    return $result;

        } catch (PDOException $e) {
            throw new Exception($e->getMessage());  
        }
  }

  // FETCH SPECIFIC DATA
  public function select_specific($query, $params = []) {
    try {
            $result = $this->connection->prepare($query);
              $result->execute($params);
                return $result;

        } catch (PDOException $e) {
            throw new Exception($e->getMessage());  
        }
  }

  // EXECUTE INSERT, UPDATE, DELETE
    public function execute_query($query, $params = []) {
        try {
            $stmt = $this->connection->prepare($query);
                $stmt->execute($params);
                    return $stmt;   

        } catch (PDOException $e) {
            throw new Exception($e->getMessage());  
        }
    }
}

问题是我收到此错误：

PHP致命错误：在第58行的/home/pipedu/public_html/msgbrd/class/DBTransaction.php中，在null上调用成员函数prepare（）

我在哪里弄错了。 当我在localhost上运行它时，它工作正常。

Answer 1

您所设置的connection类的属性，以NULL在catch内部的块DBconnection::dbConnect()与$this->connection = NULL; 。 但是，在其他功能中，您无需进行检查。 通过不为此抛出错误， 您可以使其成为类中的可接受状态 。

您的解决方案是：

1. 不要从类中的数据库连接中捕获异常，而应在初始化它的实例时捕获它，并进行相应的处理。 像这样， DBconnection->connection = NULL将在您的类中变为非法状态，您可以在其他方法中忽略这种情况。

例：

try {
    $con = new DBTransaction();
    $result = $con->select_all('SELECT * FROM table');
} catch (Exception $e) {
    $result = NULL;
}

2. 处理状态，在其他方法中DBconnection->connection可能为NULL ，并为该情况返回并分配值：

例：

public function select_all($query) {
    if (this->connection === NULL) {
        return NULL;
    }

    $result = $this->connection->query($query);
    $result->execute();
    return $result;
}