How to create constructor with optional parameters?

Question

I have __construct($parameter)

public function __construct($nick) {
    $query = "SELECT * FROM Users WHERE nick='".$nick."'";
    $result = App::runQuery($query);
    $user = $result->fetch_object();

    $this->id = $user->id;
    $this->nick = $user->nick;
    $this->email = $user->email;
    $this->password = $user->password;
    $this->birthDay = $user->birthDay;
    $this->sex = $user->sex;
    $this->about = $user->about;
    $this->city = $user->city;
    $this->photo = $user->photo;
    $this->following = $user->following;
    $this->followers = $user->followers;
    $this->statu = $user->statu; 

}

And now I want to have a default constructor without parameters like this:

public function __construct() {

    $this->id = NULL;
    $this->nick = NULL;
    $this->email = NULL;
    $this->password = NULL;
    $this->birthDay = NULL;
    $this->sex = NULL;
    $this->about = NULL;
    $this->city = NULL;
    $this->photo = NULL;
    $this->following = NULL;
    $this->followers = NULL;
    $this->statu = NULL; 

}

But something is wrong and I get error like this:

Fatal error: Cannot redeclare User::__construct() in /Applications/MAMP/htdocs/xxx/Application/User.php on line 33

How can I have two constructors with parameters and without parameters at the same time?

While you're probably not working on this two years later you have an obvious SQL injection bug in this code — Casey, Jul 27 '17 at 19:23

score 22 · Answer 1 · answered Feb 08 '15 at 15:43

There is no overloading in PHP; you cannot have methods with the same names but different parameters

Since all of your properties will default to null, there's no reason to do it yourself. I would suggest doing the following:

public function __construct($nick = null) {
    if ($nick != null) {
        $query = "SELECT * FROM Users WHERE nick='".$nick."'";
        $result = App::runQuery($query);
        $user = $result->fetch_object();

        $this->id = $user->id;
        $this->nick = $user->nick;
        $this->email = $user->email;
        $this->password = $user->password;
        $this->birthDay = $user->birthDay;
        $this->sex = $user->sex;
        $this->about = $user->about;
        $this->city = $user->city;
        $this->photo = $user->photo;
        $this->following = $user->following;
        $this->followers = $user->followers;
        $this->statu = $user->statu; 
    }
}

An alternative to the above code is to have multiple, static constructor methods, and use a private constructor:

private function __construct() {
}

public static function createFromNick($nick) {
    $self = new self();

    $query = "SELECT * FROM Users WHERE nick='".$nick."'";
    $result = App::runQuery($query);
    $user = $result->fetch_object();

    $self->id = $user->id;
    $self->nick = $user->nick;
    $self->email = $user->email;
    $self->password = $user->password;
    $self->birthDay = $user->birthDay;
    $self->sex = $user->sex;
    $self->about = $user->about;
    $self->city = $user->city;
    $self->photo = $user->photo;
    $self->following = $user->following;
    $self->followers = $user->followers;
    $self->statu = $user->statu;

    return $self;
}

public static function createEmpty() {
    return new self();
}

Note that in PHP constructors are not allowed to throw any `Throwable`s such as `Exception`s. It will just crash the execution of the PHP script. Usually database queries in PHP are allowed to throw `Exception`s. But I'm not sure what this App:: thing is in this case. — Henk Poley, Nov 27 '19 at 15:44

score 2 · Answer 2 · edited May 23 '17 at 11:47

2

public function __construct() {
    // allocate your stuff
}

public static function withRow( array $row ) {
    $instance = new self();
    $instance->fill( $row );
    return $instance;
}

protected function fill( array $row ) {
    // fill all properties from array
}

For details check this answer : Best way to do multiple constructors in PHP

edited May 23 '17 at 11:47

Community

1
1

answered Feb 08 '15 at 15:50

Md. Al-Amin

1,423
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26

score -10 · Accepted Answer · answered Feb 08 '15 at 16:48

Thank you very much for your answer. I have solved the problem with my way.

public function __construct($nick) {
    if($nick != NULL) {//for user 
        $query = "SELECT * FROM Users WHERE nick='".$nick."'";
        $result = App::runQuery($query);
        $user = $result->fetch_object();

        $this->id = $user->id;
        $this->nick = $user->nick;
        $this->email = $user->email;
        $this->password = $user->password;
        $this->birthDay = $user->birthDay;
        $this->sex = $user->sex;
        $this->about = $user->about;
        $this->city = $user->city;
        $this->photo = $user->photo;
        $this->following = $user->following;
        $this->followers = $user->followers;
        $this->statu = $user->statu; 
    }else {//for null
        $this->id = NULL;
        $this->nick = NULL;
        $this->email = NULL;
        $this->password = NULL;
        $this->birthDay = NULL;
        $this->sex = NULL;
        $this->about = NULL;
        $this->city = NULL;
        $this->photo = NULL;
        $this->following = NULL;
        $this->followers = NULL;
        $this->statu = NULL;
    }

}

It works!

I think you missed the actual point of argument being optional which was addressed by @TimCooper here is the clue `public function __construct($nick = null)` — Mubashar, Jul 12 '19 at 05:48
With PHP > 7.4 it should be `public function __construct($nick = null)`. — Alexander Behling, Dec 10 '21 at 15:36
You code works because it only has one param. Also the else part can be omit, because it is the default value of the attributes. For a constructor which needs either zero or multiple params I could only think of handling this using an array. Then I could check if the param is an array and if so check the number of entries in the array. — Alexander Behling, Dec 10 '21 at 15:49

How to create constructor with optional parameters?

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