im work with php and mysql, sometimes i need instantiate my php class in data access layer for return objects, load list etc... but sometimes I use the class constructor and others do not.
Can i create doble constructor in a class?
example:
class Student {
private $id;
private $name;
private $course;
function __construct() {
}
//get set id and name
function setCourse($course) {
$this->course = $course;
}
function getCourse() {
$this->course = $course;
}
}
class Course {
private $id;
private $description;
function __construct($id) {
this->id = $id;
}
//get set, id, description
}
In my access layer sometime I use the constructor in different ways
for example:
$result = $stmt->fetchAll();
$listStudent = new ArrayObject();
if($result != null) {
foreach($result as $row) {
$student = new Student();
$student->setId($row['id']);
$student->setName($row['name']);
$student->setCourse(new Course($row['idcourse'])); //this works
$listStudent ->append($sol);
}
}
But sometimes I need to use the constructor in another way, for example
$result = $stmt->fetchAll();
$listCourses = new ArrayObject();
if($result != null) {
foreach($result as $row) {
$course = new Course(); //but here not work, becouse Class course receives a id
$course->setId($row['idcourse']);
$course->setDescription($row['description']);
$listCourses->append($sol);
}
}
My english is very bad,
i hope you understand me
Use default arguments:
class Course {
private $id;
private $description;
function __construct($id = 0) {
this->id = $id;
}
// getters and setters for id and description
}
Now, you can use it like that:
$course = new Course(12); // works with argument
or:
$course = new Course(); // works without argument
$course->setId(12);
class Course {
private $id;
private $description;
public function __construct() {
// allocate your stuff
}
public static function constructWithID( $id ) {
$instance = new self();
//do your stuffs here
return $instance;
}
call like Course:: constructWithID(..id) when you have to pass id otherwise make object (new Course()).
Related
Haven't found an answer yet but I'm sure there must be one: how do I prevent an object recursion/loop when objects reference each other? An example:
class Patient {
private $Issues = array();
[...]
public function __construct($id) {
[ Get data from DB ]
while ($row = $result->fetch_assoc()) {
$this->Issues[$row['idIssue']] = new Issue($row['idIssue']);
}
[...]
}
}
class Issue {
private $Patient;
[...]
public function __construct($id) {
[ Get data from DB ]
$this->Patient = new Patient($row['idPatient']); <-- Leads to recursion as the patient will load all it's Issues() etc. etc.
[...]
}
}
How do I prevent this? I could use the id of the Patient() instead of the real object but that feels like a hack. Is there a way to use the real object?
Do not recreate object. Just pass the instance of the master object to the detail constructor. E.g.:
class Patient {
private $Issues = array();
[...]
public function __construct($id) {
[ Get data from DB ]
while ($row = $result->fetch_assoc()) {
$this->Issues[$row['idIssue']] = new Issue($row['idIssue'], $this);
}
[...]
}
}
class Issue {
private $Patient;
[...]
public function __construct($id, Patient $patient) {
[ Get data from DB ]
$this->Patient = $patient
[...]
}
}
You can (should !) separate the DB connection/queries from the entities definitions and pass references to relations, otherwise, you can't mock entities, plus mixing DB connection and entities definition goes against the separation of concerns :
// somewhere in your code
$idPatient = 42;
$patient = new Patient();
$patient->setId($idPatient);
// get datas from DB
while ($row = $result->fetch_assoc())
{
$issue = new Issue();
$issue->setId($row['idIssue'])
->setPatient($patient);
$patient->addIssue($issue);
// or, shorter way :
// $patient->addIssues((new Issue())->setId($row['idIssue'])
// ->setPatient($patient));
}
class Patient {
private $Issues = array();
private $Id;
public function addIssue(Issue $issue): self
{
$this->Issues[] = $issue;
return $this;
}
public function setId(int $id): self
{
$this->Id = $id;
return $this;
}
}
class Issue {
private $Patient;
private $Id;
public function addPatient(Patient $patient): self
{
$this->Patient = $patient;
return $this;
}
public function setId(int $id): self
{
$this->Id = $id;
return $this;
}
}
I've written a class which in the construct accesses the db and gets a list of names. These names go into an associative array e.g. ('name' => 'id').
i.e. the point is to pass in the name to get back an ID:
$id = names::nameToId('some name');
print $id;
// prints int
The problem is when I try and return the array from the construct I get an error:
Notice: Undefined variable: nameArray in (etc)
Here is the code so far:
class nameToId {
public $nameArray;
private $mysqli;
public function __construct($mysqli) {
...
while($row = mysqli_fetch_assoc($res)) {
$nameArray[$row['name']] = $row['id'];
}
return $nameArray;
}
static public function nameToId($name) {
$nameId = $nameArray[$name];
return $nameId;
}
}
$namesToId = new nameToId($mysqli);
$nameId = $namesToId::nameToId('some name');
echo $nameId;
Why doesn't $nameArray get passed to nameToId()? I'm new to classes, and I thought by declaring $nameArray as public when I first create the class that it would make it available. I have also tried to make it global even though I know that is not good form but even still it didn't work.
Because you cannot return anything from a constructor. Any return value is being ignored and just goes into the aether. $nameArray is a local variable and is not shared in any other scope, i.e. you can't access it in nameToId. Further, since nameToId is static, it won't have access to data from any non-static methods like __construct to begin with.
You probably want something like this:
class nameToId {
public $nameArray;
private $mysqli;
public function __construct($mysqli) {
...
while ($row = mysqli_fetch_assoc($res)) {
$this->nameArray[$row['name']] = $row['id'];
}
}
public function nameToId($name) {
return $this->nameArray[$name];
}
}
$namesToId = new nameToId($mysqli);
echo $namesToId->nameToId('some name');
Fix your code:
class nameToId {
public static $nameArray;
private $mysqli;
public function __construct($mysqli) {
$this->mysqli = $mysqli;
$sql = 'SELECT id, name FROM teams';
$res = mysqli_query($this->mysqli,$sql);
while($row = mysqli_fetch_assoc($res)) {
self::$nameArray[$row['name']] = $row['id'];
}
}
static public function nameToId($name) {
$nameId = self::$nameArray[$name];
return $nameId;
}
}
$namesToId = new nameToId($mysqli);
$nameId = $namesToId::nameToId('some name');
echo $nameId;
I think code given below works fine (I am busy on learning OOP PHP and not tested these code yet) if I want to retrieve single record. What if I want to loop the record ? How to do that ? Can I use single class to retrieve single and loop record ? If yes how ?
include('class.database.php');
class News
{
protected $id;
protected $title;
protected $detail;
protected $updatedon;
protected $views;
protected $pic;
protected $cat;
protected $reporter;
function __construct ($id);
$newsdb = new Database;
$Query = "SELECT * FROM news WHERE nws_sn =".$id;
$db->query($Query);
$db->singleRecord();
$this->id = $newsdb->Record['nws_sn'];
$this->title = $newsdb->Record['nws_title'];
$this->detail = $newsdb->Record['nws_detail'];
$this->updatedon = $newsdb->Record['nws_time'];
$this->views = $newsdb->Record['nws_view'];
$this->pic = $newsdb->Record['nws_pic'];
$this->cat = $newsdb->Record['nws_cat_id'];
$this->reporter = $newsdb->Record['nws_rptr_id']
}
function getId () {
return $this->id;
}
function getTitle () {
return $this->title;
}
function getDetail () {
return $this->detail;
}
function getViews () {
return $this->views;
}
function getImage () {
return $this->pic;
}
function getTime () {
return $this->updatedon;
}
}
You want to use a constructor to initialize an internal state of your object. In your case you do too much in your constructor which also breaks "single responsibility principle". It seems that "News" is just an entity or data transfer object, so you have to initialize it from outside.
First, I would keep News just to store information received from database.
Second, I would create a static factory method inside News class so it create an actual News object and populate it with data passed to the method from outside. Alternatively, you could create a factory object to create your entity, but since the construction logic is simple enough, I thought it makes sense to keep it inside a single method.
Consider the code below:
class News
{
protected $id;
protected $title;
protected $detail;
protected $updatedon;
protected $views;
protected $pic;
protected $cat;
protected $reporter;
public static createFromRecord($record)
{
$obj = new self();
$obj->setId($record->Record['nws_sn']);
$obj->setTitle($record->Record['nws_title']);
$obj->setDetail($record->Record['nws_detail']);
$obj->setUpdateon($record->Record['nws_time']);
$obj->setViews($record->Record['nws_view']);
$obj->setPic($record->Record['nws_pic']);
$obj->setCat($record->Record['nws_cat_id']);
$obj->setReporter($record->Record['nws_rptr_id']);
return $obj;
}
function getId () {
return $this->id;
}
function getTitle () {
return $this->title;
}
function getDetail () {
return $this->detail;
}
function getViews () {
return $this->views;
}
function getImage () {
return $this->pic;
}
function getTime () {
return $this->updatedon;
}
// ... add public setters for the properties
}
...
$newsdb = new Database;
$Query = "SELECT * FROM news WHERE nws_sn =".$id;
$db->query($Query);
$record = $db->singleRecord();
$newsObject = News::createFromRecord($record);
I have something like this:
class MyParent {
protected static $object;
protected static $db_fields;
public function delete() {
// delete stuff
}
public static function find_by_id($id = 0) {
global $database;
$result_array = self::find_by_sql("SELECT * FROM " . static::$table_name . " WHERE id=" . $database -> escape_value($id) . " LIMIT 1");
return !empty($result_array) ? array_shift($result_array) : false;
}
public static function find_by_sql($sql = "") {
global $database;
// Do Query
$result_set = $database -> query($sql);
// Get Results
$object_array = array();
while ($row = $database -> fetch_array($result_set)) {
$object_array[] = self::instantiate($row);
}
return $object_array;
}
private static function instantiate($record) {
$object = self::$object;
foreach ($record as $attribute => $value) {
if (self::has_attribute($attribute)) {
$object -> $attribute = $value;
}
}
return $object;
}
}
class TheChild extends MyParent {
protected static $db_fields = array('id', 'name');
protected static $table_name = "my_table";
function __construct() {
self::$object = new TheChild;
}
}
$child= TheChild::find_by_id($_GET['id']);
$child->delete();
I get this: Call to undefined method stdClass::delete() referring to the last line above. What step am I missing for proper inheritance?
You never actually instanciate the TheChild class, which should be done by
$var = new TheChild();
except in TheChild constructor itself.
So, the static $object field is never affected (at least in your example), so affecting a field to it (the line $object -> $attribute = $value; ) causes the creation of an stdClass object, as demonstrated in this interactive PHP shell session:
php > class Z { public static $object; }
php > Z::$object->toto = 5;
PHP Warning: Creating default object from empty value in php shell code on line 1
php > var_dump(Z::$object);
object(stdClass)#1 (1) {
["toto"]=>
int(5)
}
This object does not have a delete method.
And as said before, actually creating a TheChild instance will result in an infinite recursion.
What you want to do is this, probably:
class TheChild extends MyParent {
protected static $db_fields = array('id', 'name');
protected static $table_name = "my_table";
function __construct() {
self::$object = $this;
}
}
Edit: Your updated code shows a COMPLETE different Example:
class MyParent {
protected static $object;
public function delete() {
// delete stuff
}
}
class TheChild extends MyParent {
function __construct() {
self::$object = new TheChild;
}
}
$child = new TheChild;
$child->delete();
Calling "Child's" Constructor from within "Child's" Constructor will result in an infinite loop:
function __construct() {
self::$object = new TheChild; // will trigger __construct on the child, which in turn will create a new child, and so on.
}
Maybe - i dont know what you try to achieve - you are looking for:
function __construct() {
self::$object = new MyParent;
}
ALSO note, that the :: Notation is not just a different Version for -> - it is completely different. One is a Static access, the other is a access on an actual object instance!
I'm having problems with accessing variables from my classes...
class getuser {
public function __construct($id) {
$userquery = "SELECT * FROM users WHERE id = ".$id."";
$userresult = mysql_query($userquery);
$this->user = array();
$idx = 0;
while($user = mysql_fetch_object($userresult)){
$this->user[$idx] = $user;
++$idx;
}
}
}
I'm setting this class in a global 'classes' file, and later on I pass through a user id into the following script:
$u = new getuser($userid);
foreach($u->user as $user){
echo $user->username;
}
I'm hoping that this will give me the name of the user but it's not, where am I going wrong?!
Thanks
please define your users member as public in your class like this
class getuser {
public $user = null;
//...
}
in order to access a class property, you have to declare it public or implement getters and setters (second solution is preferable)
class A {
public $foo;
//class methods
}
$a = new A();
$a->foo = 'whatever';
with getters and setters, one per property
class B {
private $foo2;
public function getFoo2() {
return $this->foo2;
}
public function setFoo2($value) {
$this->foo2 = $value;
}
}
$b = new B();
$b->setFoo2('whatever');
echo $b->getFoo2();
in your example:
class getuser {
private $user;
public function __construct($id) {
$userquery = "SELECT * FROM users WHERE id = ".$id."";
$userresult = mysql_query($userquery);
$this->user = array();
$idx = 0;
while($user = mysql_fetch_object($userresult)){
$this->user[$idx] = $user;
++$idx;
}
}
/* returns the property value */
public function getUser() {
return $this->user;
}
/* sets the property value */
public function setUser($value) {
$this->user = $value;
}
}
$u = new getuser($userid);
$users_list = $u->getUser();
foreach($users_list as $user) {
echo $user->username;
}