PHP：变量变量中的类属性链接

Question

So, I have a object with structure similar to below, all of which are returned to me as stdClass objects

$person->contact->phone;
$person->contact->email;
$person->contact->address->line_1;
$person->contact->address->line_2;
$person->dob->day;
$person->dob->month;
$person->dob->year;
$album->name;
$album->image->height;
$album->image->width;
$album->artist->name;
$album->artist->id;

etc... (note these examples are not linked together).

Is it possible to use variable variables to call contact->phone as a direct property of $person ?

For example:

$property = 'contact->phone';
echo $person->$property;

This will not work as is and throws a E_NOTICE so I am trying to work out an alternative method to achieve this.

Any ideas?

In response to answers relating to proxy methods:

And I would except this object is from a library and am using it to populate a new object with an array map as follows:

array(
  'contactPhone' => 'contact->phone', 
  'contactEmail' => 'contact->email'
);

and then foreaching through the map to populate the new object. I guess I could envole the mapper instead...

Answer 1

If i was you I would create a simple method ->property(); that returns $this->contact->phone

Answer 2

Is it possible to use variable variables to call contact->phone as a direct property of $person?

It's not possible to use expressions as variable variable names.

But you can always cheat:

class xyz {

    function __get($name) {

        if (strpos($name, "->")) {
            foreach (explode("->", $name) as $name) {
                $var = isset($var) ? $var->$name : $this->$name;
            }
            return $var;
        }
        else return $this->$name;
    }
}

Answer 3

try this code

$property = $contact->phone;
echo $person->$property;

Answer 4

I think this is a bad thing to to as it leads to unreadable code is is plain wrong on other levels too, but in general if you need to include variables in the object syntax you should wrap it in braces so that it gets parsed first.

For example:

$property = 'contact->phone';
echo $person->{$property};

The same applies if you need to access an object that has disalowed characters in the name which can happen with SimpleXML objects regularly.

$xml->{a-disallowed-field}

Answer 5

If it is legal it does not mean it is also moral. And this is the main issue with PHP, yes, you can do almost whatever you can think of, but that does not make it right. Take a look at the law of demeter:

Law of Demeter

try this if you really really want to: json_decode(json_encode($person),true);

you will be able to parse it as an array not an object but it does your job for the getting not for the setting.

EDIT:

class Adapter {

  public static function adapt($data,$type) {

  $vars = get_class_vars($type);

  if(class_exists($type)) {
     $adaptedData = new $type();
  } else {
    print_R($data);
    throw new Exception("Class ".$type." does not exist for data ".$data);
  }

  $vars = array_keys($vars);

  foreach($vars as $v) {

    if($v) {        
      if(is_object($data->$v)) {
          // I store the $type inside the object
          $adaptedData->$v = Adapter::adapt($data->$v,$data->$v->type);
      } else {
          $adaptedData->$v =  $data->$v;
      }
    }
  }
  return $adaptedData;

  }

}

Answer 6

If you know the two function's names, could you do this? (not tested)

$a = [
    'contactPhone' => 'contact->phone', 
    'contactEmail' => 'contact->email'
];

foreach ($a as $name => $chain) {
    $std = new stdClass();
    list($f1, $f2) = explode('->', $chain);
    echo $std->{$f1}()->{$f2}(); // This works
}

If it's not always two functions, you could hack it more to make it work. Point is, you can call chained functions using variable variables, as long as you use the bracket format.

Answer 7

OOP is much about shielding the object's internals from the outside world. What you try to do here is provide a way to publicize the innards of the phone through the person interface. That's not nice.

If you want a convenient way to get "all" the properties, you may want to write an explicit set of convenience functions for that, maybe wrapped in another class if you like. That way you can evolve the supported utilities without having to touch (and possibly break) the core data structures:

class conv {
 static function phone( $person ) {
   return $person->contact->phone;
 }

}

// imagine getting a Person from db
$person = getpersonfromDB();

print conv::phone( $p );

If ever you need a more specialized function, you add it to the utilities. This is imho the nices solution: separate the convenience from the core to decrease complexity, and increase maintainability/understandability.

Another way is to 'extend' the Person class with conveniences, built around the core class' innards:

class ConvPerson extends Person {
   function __construct( $person ) {
     Person::__construct( $person->contact, $person->name, ... );
   }
   function phone() { return $this->contact->phone; }
}

// imagine getting a Person from db
$person = getpersonfromDB();
$p=new ConvPerson( $person );
print $p->phone();

Answer 8

You could use type casting to change the object to an array.

$person = (array) $person;

echo $person['contact']['phone'];

Answer 9

In most cases where you have nested internal objects, it might be a good time to re-evaluate your data structures.

In the example above, person has contact and dob . The contact also contains address . Trying to access the data from the uppermost level is not uncommon when writing complex database applications. However, you might find your the best solution to this is to consolidate data up into the person class instead of trying to essentially "mine" into the internal objects.

Answer 10

As much as I hate saying it, you could do an eval :

foreach ($properties as $property) {
     echo eval("return \$person->$property;");
}

Answer 11

Besides making function getPhone(){return $this->contact->phone;} you could make a magic method that would look through internal objects for requested field. Do remember that magic methods are somewhat slow though.

class Person {
    private $fields = array();

    //...

    public function __get($name) {
        if (empty($this->fields)) {
            $this->fields = get_class_vars(__CLASS__);
        }
        //Cycle through properties and see if one of them contains requested field:
        foreach ($this->fields as $propName => $default) {
            if (is_object($this->$propName) && isset($this->$propName->$name)) {
                return $this->$propName->$name;
            }
        }
        return NULL;
        //Or any other error handling
    }
}

Answer 12

I have decided to scrap this whole approach and go with a more long-winded but cleaner and most probably more efficient. I wasn't too keen on this idea in the first place, and the majority has spoken on here to make my mind up for me. Thank for you for your answers.

Edit:

If you are interested:

public function __construct($data)
{
  $this->_raw = $data;
}

public function getContactPhone()
{
  return $this->contact->phone;
}

public function __get($name) 
{
  if (isset($this->$name)) {
    return $this->$name;
  }

  if (isset($this->_raw->$name)) {
    return $this->_raw->$name;
  }

  return null;
}

Answer 13

In case you use your object in a struct-like way, you can model a 'path' to the requested node explicitly. You can then 'decorate' your objects with the same retrieval code.

An example of 'retrieval only' decoration code:

function retrieve( $obj, $path ) {
    $element=$obj;
    foreach( $path as $step ) { 
       $element=$element[$step];
    }
    return $element;
}

function decorate( $decos, &$object ) {
   foreach( $decos as $name=>$path ) {
      $object[$name]=retrieve($object,$path);
   }
}

$o=array( 
  "id"=>array("name"=>"Ben","surname"=>"Taylor"),
  "contact"=>array( "phone"=>"0101010" )
);

$decorations=array(
  "phone"=>array("contact","phone"),
  "name"=>array("id","name")  
);

// this is where the action is
decorate( $decorations, &$o);
print $o->name;
print $o->phone;

(find it on codepad )

Answer 14

Simplest and cleanest way I know of.

function getValueByPath($obj,$path) {
    return eval('return $obj->'.$path.';');
}

Usage

echo getValueByPath($person,'contact->email');
// Returns the value of that object path