适配模式

$db = new IMooc\Database\MySQL();
//$db = new IMooc\Database\MySQLi();
//$db = new IMooc\Database\PDO();
$db->connect(‘127.0.0.1‘, ‘root‘, ‘root‘, ‘test‘);
$db->query("show databases");
$db->close();

<?php
namespace IMooc;

interface IDatabase
{
    function connect($host, $user, $passwd, $dbname);
    function query($sql);
    function close();
}

<?php
namespace IMooc\Database;

use IMooc\IDatabase;

class MySQL implements IDatabase
{
    protected $conn;
    function connect($host, $user, $passwd, $dbname)
    {
        $conn = mysql_connect($host, $user, $passwd);
        mysql_select_db($dbname, $conn);
        $this->conn = $conn;
    }

    function query($sql)
    {
        $res = mysql_query($sql, $this->conn);
        return $res;
    }

    function close()
    {
        mysql_close($this->conn);
    }
}

<?php
namespace IMooc\Database;

use IMooc\IDatabase;

class MySQLi implements IDatabase
{
    protected $conn;

    function connect($host, $user, $passwd, $dbname)
    {
        $conn = mysqli_connect($host,$user,$passwd,$dbname);
        $this->conn = $conn;
    }

    function query($sql)
    {
        return mysqli_query($this->conn, $sql);
    }

    function close()
    {
        mysqli_close($this->conn);
    }
}

<?php
namespace IMooc\Database;

use IMooc\IDatabase;

class PDO implements IDatabase
{
    protected $conn;
    function connect($host, $user, $passwd, $dbname)
    {
        $conn = new \PDO("mysql:host=$host;dbname=$dbname", $user, $passwd);
        $this->conn = $conn;
    }

    function query($sql)
    {
        return $this->conn->query($sql);
    }

    function close()
    {
        unset($this->conn);
    }
}