重新启程：php底层框架篇（PDO）

一直在使用框架，如今脱离了框架居然发现自己不会写程序了，这两天一直在做一个程序安全方面的应用，程序很老旧，代码质量很糟糕，我决定重新去构建这套系统，但是使用自己得框架

第一篇PDO数据库底层操作篇

    private $db;
    private $trans_ing = false;
    private $db_err;

    public function __construct()
    {
        $dsn = 'mysql:host=' . DB_HOST . ';dbname=' . DB_NAME . ';port=' . DB_PORT;
        for ($i = 0; $i < 3; $i++) {
            try {
                $this->db = new PDO($dsn, DB_USER, DB_PASS, array(
                    PDO::ATTR_PERSISTENT => false,
                    PDO::ATTR_CASE => PDO::CASE_NATURAL,
                    PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
                    PDO::ATTR_AUTOCOMMIT => true,
                    PDO::MYSQL_ATTR_USE_BUFFERED_QUERY => true,
                    PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES utf8',
                ));
                break;
            } catch (Exception $e) {
                if ($i >= 2) throw new Exception('连接数据库失败，请重试');
            }
        }
    }

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

    //插入
    public function insert($table, $data)
    {
        $fields = '';
        $values = '';
        $realValues = array();
        foreach ($data as $k => $v) {
            if ($v === null) {
                continue;
            }
            $fields .= '`' . $k . '`,';
            $values .= ":{$k},";
            $realValues[":{$k}"] = strval($v);
        }
        $sql = 'INSERT INTO `' . $table . '` (' . substr($fields, 0, -1) . ') VALUES (' . substr($values, 0, -1) . ')';
        $pre = $this->db->prepare($sql);
        if (!$pre) {
            return false;
        }
        $result = $pre->execute($realValues);
        if ($result) {
            return $this->db->lastInsertId();
        }
        return false;
    }


    //更新
    public function update($table, $data, $where = array())
    {
        $fields = '';
        $realValues = array();
        foreach ($data as $k => $v) {
            if ($v === null) {
                continue;
            }
            $fields .= ",`{$k}`=:{$k}";
            $realValues[":{$k}"] = strval($v);
        }
        $fields = substr($fields, 1, strlen($fields) - 1);

        $whereSql = '';
        $whereValues = array();
        foreach ($where as $k => $v) {
            $whereSql .= " AND `{$k}`=:{$k}_1";
            $whereValues[":{$k}_1"] = strval($v);
        }
        $realValues = array_merge($whereValues, $realValues);
        $sql = "UPDATE `{$table}` SET {$fields} WHERE 1 {$whereSql}";
        $pre = $this->db->prepare($sql);
        if (!$pre) {
            return false;
        }
        try {
            $ret = $pre->execute($realValues);
            return $ret;
        } catch (Exception $e) {
            $this->db_err = $e->getMessage();
            return false;
        }
    }