PHP单例模式

<?php
class db {
public $conn;
public static $sql;
public static $instance=null;
private function __construct(){
require_once(‘db.config.php‘);
$this->conn = mysql_connect($db[‘host‘],$db[‘user‘],$db[‘password‘]);
if(!mysql_select_db($db[‘database‘],$this->conn)){
echo "失败";
};
mysql_query(‘set names utf8‘,$this->conn);
}
public static function getInstance(){
if(is_null(self::$instance)){
self::$instance = new db;
}
return self::$instance;
}
/**
* 查询数据库
*/
public function select($table,$condition=array(),$field = array()){
$where=‘‘;
if(!empty($condition)){

foreach($condition as $k=>$v){
$where.=$k."=‘".$v."‘ and ";
}
$where=‘where ‘.$where .‘1=1‘;
}
$fieldstr = ‘‘;
if(!empty($field)){

foreach($field as $k=>$v){
$fieldstr.= $v.‘,‘;
}
$fieldstr = rtrim($fieldstr,‘,‘);
}else{
$fieldstr = ‘*‘;
}
self::$sql = "select {$fieldstr} from {$table} {$where}";
$result=mysql_query(self::$sql,$this->conn);
$resuleRow = array();
$i = 0;
while($row=mysql_fetch_assoc($result)){
foreach($row as $k=>$v){
$resuleRow[$i][$k] = $v;
}
$i++;
}
return $resuleRow;
}
/**
* 添加一条记录
*/
public function insert($table,$data){
$values = ‘‘;
$datas = ‘‘;
foreach($data as $k=>$v){
$values.=$k.‘,‘;
$datas.="‘$v‘".‘,‘;
}
$values = rtrim($values,‘,‘);
$datas = rtrim($datas,‘,‘);
self::$sql = "INSERT INTO {$table} ({$values}) VALUES ({$datas})";
if(mysql_query(self::$sql)){
return mysql_insert_id();
}else{
return false;
};
}
/**
* 修改一条记录
*/
public function update($table,$data,$condition=array()){
$where=‘‘;
if(!empty($condition)){

foreach($condition as $k=>$v){
$where.=$k."=‘".$v."‘ and ";
}
$where=‘where ‘.$where .‘1=1‘;
}
$updatastr = ‘‘;
if(!empty($data)){
foreach($data as $k=>$v){
$updatastr.= $k."=‘".$v."‘,";
}
$updatastr = ‘set ‘.rtrim($updatastr,‘,‘);
}
self::$sql = "update {$table} {$updatastr} {$where}";
return mysql_query(self::$sql);
}
/**
* 删除记录
*/
public function delete($table,$condition){
$where=‘‘;
if(!empty($condition)){

foreach($condition as $k=>$v){
$where.=$k."=‘".$v."‘ and ";
}
$where=‘where ‘.$where .‘1=1‘;
}
self::$sql = "delete from {$table} {$where}";
return mysql_query(self::$sql);

}

public static function getLastSql(){
echo self::$sql;
}



}

$db = db::getInstance();
//$list = $db->select(‘demo‘,array(‘name‘=>‘tom‘,‘password‘=>‘ds‘),array(‘name‘,‘password‘));
//echo $db->insert(‘demo‘,array(‘name‘=>‘最近你啦‘,‘password‘=>‘123‘));
//echo $db->update(‘demo‘,array("name"=>‘xxx‘,"password"=>‘123‘),array(‘id‘=>1));
echo $db->delete(‘demo‘,array(‘id‘=>‘2‘));
db::getLastSql();
echo "<pre>";
?>