php单例模式（多次连接数据库只实例化一次）
1. <?php2. class db {
3. public $conn;
4. public static $sql;
5. public static $instance=null;
6. private function __construct(){
7. require_once('db.config.php');
8. $this->conn = mysql_connect($db['host'],$db['user'],$db['password']);
9. if(!mysql_select_db($db['database'],$this->conn)){
10. echo "失败";
11. };
12. mysql_query('set names utf8',$this->conn);
13. }
14. public static function getInstance(){
15. if(is_null(self::$instance)){
16. self::$instance = new db;
17. }
18. return self::$instance;
19. }
20. /**
21. * 查询数据库
22. */
23. public function select($table,$condition=array(),$field = array()){
24. $where='';
25. if(!empty($condition)){
26.
27. foreach($condition as $k=>$v){
28. $where.=$k."='".$v."' and ";
29. }
30. $where='where '.$where .'1=1';
31. }
32. $fieldstr = '';
33. if(!empty($field)){
34.
35. foreach($field as $k=>$v){
36. $fieldstr.= $v.',';
37. }
38. $fieldstr = rtrim($fieldstr,',');
39. }else{
40. $fieldstr = '*';
41. }
42. self::$sql = "select {$fieldstr} from {$table} {$where}";
43. $result=mysql_query(self::$sql,$this->conn);
44. $resuleRow = array();
45. $i = 0;
46. while($row=mysql_fetch_assoc($result)){
47. foreach($row as $k=>$v){
48. $resuleRow[$i][$k] = $v;
49. }
50. $i++;
51. }
52. return $resuleRow;
53. }
54. /**
55. * 添加一条记录
56. */
57. public function insert($table,$data){
58. $values = '';
59. $datas = '';
60. foreach($data as $k=>$v){
61. $values.=$k.',';
62. $datas.="'$v'".',';
63. }
64. $values = rtrim($values,',');
65. $datas = rtrim($datas,',');
66. self::$sql = "INSERT INTO{$table} ({$values}) VALUES ({$datas})";
67. if(mysql_query(self::$sql)){
68. return mysql_insert_id();
69. }else{
70. return false;
71. };
72. }
73. /**
74. * 修改一条记录
75. */
76. public function update($table,$data,$condition=array()){
77. $where='';
78. if(!empty($condition)){
79.
80. foreach($condition as $k=>$v){
81. $where.=$k."='".$v."' and ";
82. }
83. $where='where '.$where .'1=1';
84. }
85. $updatastr = '';
86. if(!empty($data)){
87. foreach($data as $k=>$v){
88. $updatastr.= $k."='".$v."',";
89. }
90. $updatastr = 'set '.rtrim($updatastr,',');
91. }
92. self::$sql = "update {$table} {$updatastr} {$where}";
93. return mysql_query(self::$sql);
94. }
95. /**
96. * 删除记录
97. */
98. public function delete($table,$condition){
99. $where='';
100. if(!empty($condition)){
101.
102. foreach($condition as $k=>$v){
103. $where.=$k."='".$v."' and ";
104. }
105. $where='where '.$where .'1=1';
106. }
107. self::$sql = "delete from {$table} {$where}";
108. return mysql_query(self::$sql);
109.
110. }
111.
112. public static function getLastSql(){
113. echo self::$sql;
114. }
115.
116.
117.
118.}
119.
120.$db = db::getInstance();
121.//$list = $db->select('demo',array('name'=>'tom','password'=>'ds'),array('name','password'));
122.//echo $db->insert('demo',array('name'=>'最近你啦','password'=>'123'));
123.//echo $db->update('demo',array("name"=>'xxx',"password"=>'123'),array('id'=>1));
124.echo $db->delete('demo',array('id'=>'2'));
125.db::getLastSql();
126.echo "<pre>";
127.?>
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