基于php和mysql的简单的dao类实现crud操作功能

<?php
    //require_once('FirePHPCore/FirePHP.class.php');
    //$firephp = FirePHP::getInstance(true); // debugger in firefox
    class SimpleDao {
        private $_table = null;
        private static $_con = null;

public function SimpleDao() {
            if ($this->_con == null) {
                $this->_con = @mysql_connect("localhost", "root", "123456");
                if ($this->_con == FALSE) {
                    echo("connect to db server failed.");
                    $this->_con = null;
                    return;
                }
                //$firephp->log("new DAO object");
                @mysql_select_db("swan", $this->_con);
            }
        }

public function table($tablename) {
            $this->_table = $tablename;
            return $this;
        }

public function query($sql) {
            $result = @mysql_query($sql);
            $ret = [];
            if ($result) {
                while ($row = mysql_fetch_array($result)) {
                    $ret[] = $row;
                }
            }
            return $ret;
        }

public function get($where = null) {
            $sql = "select * from ".$this->_table;
            $sql = $sql.$this->_getWhereString($where);
            //echo "[get]".$sql."<br>";
            return $this->query($sql);
        }

public function insert($params) {
            if ($params == null || !is_array($params)) {
                return -1;
            }
            $keys = $this->_getParamKeyString($params);
            $vals = $this->_getParamValString($params);
            $sql = "insert into ".$this->_table."(".$keys.") values(".$vals.")";
            //echo "[insert]".$sql."<br>";
            $result = @mysql_query($sql);
            if (! $result) {
                return -1;
            }
            return @mysql_insert_id();
        }

public function update($params, $where = null) {
            if ($params == null || !is_array($params)) {
                return -1;
            }
            $upvals = $this->_getUpdateString($params);
            $wheres = $this->_getWhereString($where);
            $sql = "update ".$this->_table." set ".$upvals." ".$wheres;
            //echo "[update]".$sql."<br>";
            $result = @mysql_query($sql);
            if (! $result) {
                return -1;
            }
            return @mysql_affected_rows();
        }