Extending a class from the class which is extended from mysqli - php

Question

I am not sure if this is possible as I am not very good in OOP programming yet.
I have this db class extended from mysqli,
class database extends mysqli
{
# overwrite parent __construct
public function __construct($hostname = null,$username = null,$password = null,$database = null,$port = null, $socket = null)
{
$hostname = $hostname !== null ? $hostname : ini_get("mysqli.default_host");
$username = $username !== null ? $username : ini_get("mysqli.default_user");
$password = $password !== null ? $password : ini_get("mysqli.default_pw");
$database = $database !== null ? $database : "";
$port = $port !== null ? $port : ini_get("mysqli.default_port");
$socket = $socket !== null ? $socket : ini_get("mysqli.default_socket");
parent::__construct($hostname,$username,$password,$database,$port,$socket);
# check if connect errno is set
if (mysqli_connect_errno())
{
throw new RuntimeException('Cannot access database: ' . mysqli_connect_error());
}
}
# fetches all result rows as an associative array, a numeric array, or both
# mysqli_fetch_all (PHP 5 >= 5.3.0)
public function fetch_all($query)
{
$result = parent::query($query);
if($result)
{
# check if mysqli_fetch_all function exist or not
if(function_exists('mysqli_fetch_all'))
{
# NOTE: this below always gets error on certain live server
# Fatal error: Call to undefined method mysqli_result::fetch_all() in /.../class_database.php on line 28
return $result->fetch_all(MYSQLI_ASSOC);
}
# fall back to use while to loop through the result using fetch_assoc
else
{
while($row = $result->fetch_assoc())
{
$return_this[] = $row;
}
if (isset($return_this))
{
return $return_this;
}
else
{
return false;
}
}
}
else
{
return self::get_error();
}
}
# fetch a result row as an associative array
public function fetch_assoc($query)
{
$result = parent::query($query);
if($result)
{
return $result->fetch_assoc();
}
else
{
# call the get_error function
return self::get_error();
# or:
# return $this->get_error();
}
}
public function query($query)
{
$result = $this->query($query);
if($result)
{
return $result;
}
else
{
return $this->get_error();
}
}
...
# display error
public function get_error()
{
if($this->errno || $this->error)
{
return sprintf("Error (%d): %s",$this->errno,$this->error);
}
}
public function __destruct()
{
parent::close();
//echo "Destructor Called";
}
}
and I have this procedural style of code which I want to turn it into a class that extended from the database class above,
if(isset($_REQUEST['search'])) $search = $_REQUEST['search'];
$sql = "
SELECT *
FROM root_pages
WHERE root_pages.pg_cat_id = '2'
AND root_pages.parent_id != root_pages.pg_id
AND root_pages.pg_hide != '1'
AND root_pages.pg_url != 'cms'
AND root_pages.pg_content_1 LIKE '%".$search."%'
OR root_pages.pg_content_2 LIKE '%".$search."%'
AND root_pages.pg_content_1 NOT LIKE '%http://%'
AND root_pages.pg_content_2 NOT LIKE '%http://%'
ORDER BY root_pages.pg_created DESC
";
$items = $connection->fetch_all($sql);
$total_item = $connection->num_rows($sql);
so I think, by theory I can extend this code into a class like this,
class search extends database
{
public $search = null;
public function __construct($keyword)
{
$this->search = $keyword;
}
public function get_result()
{
$sql = "
SELECT*
FROM root_pages
WHERE root_pages.pg_cat_id = '2'
AND root_pages.parent_id != root_pages.pg_id
AND root_pages.pg_hide != '1'
AND root_pages.pg_url != 'cms'
AND root_pages.pg_content_1 LIKE '%".$this->search."%'
OR root_pages.pg_content_2 LIKE '%".$this->search."%'
AND root_pages.pg_content_1 NOT LIKE '%http://%'
AND root_pages.pg_content_2 NOT LIKE '%http://%'
ORDER BY root_pages.pg_created DESC
";
$items = parent::fetch_all($sql);
return $items;
}
}
then I call the object of search,
$output = new search('1');
print_r($output->get_result());
but I get lots of errors instead,
Warning: mysqli::query()
[mysqli.query]: Couldn't fetch search
in C:\wamp\www\xxx\class_database.php
on line xx
Warning: database::get_error()
[database.get-error]: Couldn't fetch
search in
C:\wamp\www\xxx\class_database.php on
line xx
Warning: mysqli::close()
[mysqli.close]: Couldn't fetch search
in C:\wamp\www\xxx\class_database.php
on line xx
What have I done incorrectly? How can I fix it?
Thanks.
EDIT:
When I tried to call the child class (search) from the parent class (database) in this way,
$database = new database(DB_HOST,DB_USER,DB_PASS,DB_NAME);
print_r(search::get_result());
then I get this error,
Fatal error: Non-static method
mysqli::query() cannot be called
statically in
C:\wamp\www\xxx\class_database.php on
line
Sigh...
Any ideas?

Answer 1

Because the search property in the search class is non-static, you have to first instantiate an object:
$database = new database(DB_HOST,DB_USER,DB_PASS,DB_NAME);
$search = new search("search term");
print_r($search->get_result());
Maybe have a read of a basic tutorial on OOP in PHP, the first one from Google:
http://www.killerphp.com/tutorials/object-oriented-php/
EDIT: There's also a few calls to self::get_error(); in your database class, these should be re-written as instance methods rather than class methods:
$this->get_error()

Answer 2

You are using the wrong method to call methods of the mysqli class in your database class.
You only want to use the double colon :: when accessing static methods, static properties, constants, or the parent of the current method you are overwriting. None of the methods in the mysqli class are static despite how the php manual lists them with the :: in the list of methods.
The way you use parent::__construct() in your __construct() is correct because you are in the current method of the parent you are overwriting.
But in your other methods you want to use $this-> to refer to other parent methods.
In fetch_all() and fetch_assoc() use $this->query() instead of parent::query().
In __destruct() use $this->close(); instead.
When you use self::get_error();, you will either want to change that to $this-> or modify your the function definition to make it static like so public static function get_error()

Answer 3

I think extending the class from database class is probably a bad idea...
Here is my solution:
class search
{
public $mysqli = null;
public function __construct($mysqli)
{
$this->mysqli = $mysqli;
}
public function get_result($parameter)
{
$sql = "
SELECT *
FROM root_contacts_cfm
WHERE root_contacts_cfm.cnt_id = '".$parameter."'
ORDER BY cnt_id DESC
";
$item = $this->mysqli->fetch_assoc($sql);
return $item;
}
}
Passing the object database class into the search class instead, so I can call this search class by this:
$mysqli = new database(DB_HOST,DB_USER,DB_PASS,DB_NAME);
$output = new search($mysqli);
print_r($output->get_result('1'));
Am I right...?