PHP OOP MySQL连接

Question

Ok, so I am a complete beginner at OOP in php, and I thought I would try something easy to start with, however it it not working how I would expect

<?php 

class mySQL{

  var $host;
  var $username;
  var $password;
  var $database;

  public function connect($set_host, $set_username, $set_password, $set_database){
    $this->host = $set_host;
    $this->username = $set_username;
    $this->password = $set_password;
    $this->database = $set_database;

    mysql_connect("$host", "$username", "$password")or die("cannot connect");
    mysql_select_db("$database")or die("cannot select DB");

  }

}

$connect = new mySQL();
$connect -> connect('localhost', 'user', 'pass', 'database1');

$settings_query = mysql_query("SELECT * FROM settings");
$settings = mysql_fetch_array($settings_query);

echo $settings['title']; 

?>

All I am getting is "cannot connect" on my page.

Answer 1

In your connect method, you are trying to use the following variables :

• $host
• $username
• $password
• $database

that would be local to your connect() method.
But those variables don't exist.

Instead, if you want to use the properties $host , $username , and $password that are defined in your class, you must use $this to access them :

• $this->host
• $this->username
• $this->password
• $this->database

For more informations, take a look at this page of the PHP manual -- and you might want to read more about Classes and Objects .

Answer 2

mysql_connect("$host", "$username", "$password")or die("cannot connect");

$host is not defined anywhere. It needs to be mysql_connect( $this->host, $this->username, $this->password ); per your own code above.

Or perhaps you just copy pasted the mysql connect line?

Answer 3

class mySQL{

  var $host;
  var $username;
  var $password;
  var $database;
  public $dbh;  //Variable for storing connection

  public function connect($set_host, $set_username, $set_password, $set_database){
    $this->host = $set_host;
    $this->username = $set_username;
    $this->password = $set_password;
    $this->database = $set_database;

    $this->dbh = mysql_connect($this->host, $this->username, $this->password)or die("cannot connect"); //Store data connection specifier in object
    mysql_select_db($this->database)or die("cannot select DB");

  }

  public function query($sql)
  {
       return mysql_query($sql,$this->dbh);  //Specify connection handler when doing query
  }

  public function fetch($sql)
  {
       return mysql_fetch_array($this->query($sql));
  }

}
$connect = new mySQL();
$connect->connect('localhost', 'user', 'pass', 'database1');
$settings_query = mysql_query("SELECT * FROM settings", $connect->dbh); //Specify connection handler when doing query
$settings = mysql_fetch_array($settings_query);

//With query method in object you can do this:    
$settings_query = $connect->query("SELECT * FROM settings");  //Use object method to query
$settings = mysql_fetch_array($settings_query);

//with fetch method in object you can just do this:
$settings = $connect->fetch("SELECT * FROM settings");

echo $settings['title']; 

Specifying the connection handler, especially easy with a query method, allows you to easily do stuff like:

$connect1 = new MySQL();
$connect2 = new MySQL();
$connect1->connect('localhost','user','pass','database1');
$connect2->connect('localhost','user','pass','database2');

and easily handle more than one sql object/database connection at once, and helps alleviate any confusion that may arise.

This is, of course, in addition to properly referring to the objects variables within itself( $this->var ).

Answer 4

改成

mysql_connect( $this->host,  $this->username, $this->password)or die("cannot connect");

Answer 5

You probably want $this :

mysql_connect("{$this->host}", "{$this->username}", "{$this->password}")or die("cannot connect");
mysql_select_db("{$this->database}")or die("cannot select DB");

Answer 6

class mySQL{

  public function connect($set_host, $set_username, $set_password, $set_database){

    mysql_connect("$set_host", "$set_username", "$set_password")or die("cannot connect");
    mysql_select_db("$set_database")or die("cannot select DB");

  }

}

Actually this seemed to work fine for me..