这次作业比较迷，还在懵逼中
目前只改写了PDOModle.class.php文件，其他几个文件之间的逻辑关系还没搞清楚emmmmm

<?php//这里是PDOModle.class.php，大体是根据社长给的Modle.class.php改写的

namespace MyProject;
require_once ("iModel.php");

class PDOModel implements iModel
{
    protected $connection;//储存一个POD对象

    protected $sql;//储存sql语句

    protected $exec_line;//储存exec函数执行所改变的行数

    // your code

    public function __construct($dbDsn, $dbUsername, $dbPassWord)
    {
        $this->connection = new \PDO($dbDsn, $dbUsername, $dbPassWord);
    }

    public function hasError()
    {
        return $this->connection->errorCode() ? true : false;
    }

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

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

    public function update(string $statement)
    {
        $this->sql = $statement;
        $this->exec_line = $this->sql();
        if ($this->hasError()) {
            return null;
        }
        echo "update" . $this->exec_line . "rows\n";
    }

    public function insert(string $statement)
    {
        $this->sql = $statement;
        $this->exec_line = $this->sql();
        if ($this->hasError()) {
            return null;
        }
        echo "insert" . $this->exec_line . "rows\n";
    }

    public function delete(string $statement)
    {
        $this->sql = $statement;
        $this->exec_line = $this->sql();
        if ($this->hasError()) {
            return null;
        }
        echo "delete" . $this->exec_line . "rows\n";
    }

    public function select(string $statement)
    {
        $this->sql = $statement;
        $result = $this->connection->query($this->sql);
        if ($this->hasError()) {
            return null;
        }
        echo $result->fetch(\PDO::FETCH_ASSOC);
    }

    public function __destruct()
    {
        // TODO: Implement __destruct() method.
        if ($this->connection)
            $this->connection = NULL;
    }

}

目前还未测试emmmm