你不能在一个PHP类中放入两个具有唯一参数签名的__construct函数。我想这样做:
class Student
{
protected $id;
protected $name;
// etc.
public function __construct($id){
$this->id = $id;
// other members are still uninitialized
}
public function __construct($row_from_database){
$this->id = $row_from_database->id;
$this->name = $row_from_database->name;
// etc.
}
}
PHP中最好的方法是什么?
我知道我在这方面非常晚,但我提出了一个相当灵活的模式,应该允许一些真正有趣和通用的实现。
像往常一样设置类,使用您喜欢的任何变量。
class MyClass{
protected $myVar1;
protected $myVar2;
public function __construct($obj = null){
if($obj){
foreach (((object)$obj) as $key => $value) {
if(isset($value) && in_array($key, array_keys(get_object_vars($this)))){
$this->$key = $value;
}
}
}
}
}
When you make your object just pass an associative array with the keys of the array the same as the names of your vars, like so...
$sample_variable = new MyClass([
'myVar2'=>123,
'i_dont_want_this_one'=> 'This won\'t make it into the class'
]);
print_r($sample_variable);
The print_r($sample_variable); after this instantiation yields the following:
MyClass Object ( [myVar1:protected] => [myVar2:protected] => 123 )
Because we've initialize $group to null in our __construct(...), it is also valid to pass nothing whatsoever into the constructor as well, like so...
$sample_variable = new MyClass();
print_r($sample_variable);
Now the output is exactly as expected:
MyClass Object ( [myVar1:protected] => [myVar2:protected] => )
The reason I wrote this was so that I could directly pass the output of json_decode(...) to my constructor, and not worry about it too much.
This was executed in PHP 7.1. Enjoy!
从5.4版开始,PHP支持trait。这并不是你真正想要的,但基于特征的简单方法是:
trait StudentTrait {
protected $id;
protected $name;
final public function setId($id) {
$this->id = $id;
return $this;
}
final public function getId() { return $this->id; }
final public function setName($name) {
$this->name = $name;
return $this;
}
final public function getName() { return $this->name; }
}
class Student1 {
use StudentTrait;
final public function __construct($id) { $this->setId($id); }
}
class Student2 {
use StudentTrait;
final public function __construct($id, $name) { $this->setId($id)->setName($name); }
}
我们最终得到两个类,每个构造函数一个,这有点适得其反。为了保持理智,我将加入一个工厂:
class StudentFactory {
static public function getStudent($id, $name = null) {
return
is_null($name)
? new Student1($id)
: new Student2($id, $name)
}
}
所以,这一切都归结为:
$student1 = StudentFactory::getStudent(1);
$student2 = StudentFactory::getStudent(1, "yannis");
这是一个非常冗长的方法,但它可以非常方便。
这里有一种优雅的方法。创建trait,在给定参数数量的情况下启用多个构造函数。你只需将参数的数量添加到函数名“__construct”中。所以一个参数是"__construct1",两个"__construct2"…等。
trait constructable
{
public function __construct()
{
$a = func_get_args();
$i = func_num_args();
if (method_exists($this,$f='__construct'.$i)) {
call_user_func_array([$this,$f],$a);
}
}
}
class a{
use constructable;
public $result;
public function __construct1($a){
$this->result = $a;
}
public function __construct2($a, $b){
$this->result = $a + $b;
}
}
echo (new a(1))->result; // 1
echo (new a(1,2))->result; // 3
为了回应Kris的最佳答案(顺便说一句,他帮助我设计了自己的课程),这里有一个修改过的版本,供那些可能会觉得有用的人使用。包括用于从任何列中进行选择和从数组中转储对象数据的方法。干杯!
public function __construct() {
$this -> id = 0;
//...
}
public static function Exists($id) {
if (!$id) return false;
$id = (int)$id;
if ($id <= 0) return false;
$mysqli = Mysql::Connect();
if (mysqli_num_rows(mysqli_query($mysqli, "SELECT id FROM users WHERE id = " . $id)) == 1) return true;
return false;
}
public static function FromId($id) {
$u = new self();
if (!$u -> FillFromColumn("id", $id)) return false;
return $u;
}
public static function FromColumn($column, $value) {
$u = new self();
if (!$u -> FillFromColumn($column, $value)) return false;
return $u;
}
public static function FromArray($row = array()) {
if (!is_array($row) || $row == array()) return false;
$u = new self();
$u -> FillFromArray($row);
return $u;
}
protected function FillFromColumn($column, $value) {
$mysqli = Mysql::Connect();
//Assuming we're only allowed to specified EXISTENT columns
$result = mysqli_query($mysqli, "SELECT * FROM users WHERE " . $column . " = '" . $value . "'");
$count = mysqli_num_rows($result);
if ($count == 0) return false;
$row = mysqli_fetch_assoc($result);
$this -> FillFromArray($row);
}
protected function FillFromArray(array $row) {
foreach($row as $i => $v) {
if (isset($this -> $i)) {
$this -> $i = $v;
}
}
}
public function ToArray() {
$m = array();
foreach ($this as $i => $v) {
$m[$i] = $v;
}
return $m;
}
public function Dump() {
print_r("<PRE>");
print_r($this -> ToArray());
print_r("</PRE>");
}
我可能会这样做:
<?php
class Student
{
public function __construct() {
// allocate your stuff
}
public static function withID( $id ) {
$instance = new self();
$instance->loadByID( $id );
return $instance;
}
public static function withRow( array $row ) {
$instance = new self();
$instance->fill( $row );
return $instance;
}
protected function loadByID( $id ) {
// do query
$row = my_awesome_db_access_stuff( $id );
$this->fill( $row );
}
protected function fill( array $row ) {
// fill all properties from array
}
}
?>
然后,如果我想要一个学生,我知道ID:
$student = Student::withID( $id );
或者如果我有一个db行数组:
$student = Student::withRow( $row );
从技术上讲,您不需要构建多个构造函数,而只是静态帮助方法,但是这样可以避免构造函数中的大量意大利面条代码。