What's the fastest way to compare two objects in PHP?

Question

Let\'s say I have an object - a User object in this case - and I\'d like to be able to track changes to with a separate class. The User object should not have to change it\'s be

Answer 1

Here is a piece of code that supports private properties:

$reflection_1 = new \ReflectionClass($object_1);
$reflection_2 = new \ReflectionClass($object_2);

$props_1 = $reflection_1->getProperties();

foreach ($props_1 as $prop_1) {

    $prop_1->setAccessible(true);
    $value_1 = $prop_1->getValue($object_1);

    $prop_2 = $reflection_2->getProperty($prop_1->getName());

    $prop_2->setAccessible(true);
    $value_2 = $prop_2->getValue($object_2);

    if ($value_1 === $value_2) {
        // ...
    } else {
        // ...
    }
}

Note that if $object_1 has properties that $object_2 doesn't have, the above code will produce errors when trying to access them.

For such a case, you would need first to intersect $reflection_1->getProperties() with $reflection_2->getProperties().

Answer 2

There is a whole site on php.net only dealing with comparing objects:

http://php.net/manual/en/language.oop5.object-comparison.php

Also a good read:

http://www.tuxradar.com/practicalphp/6/12/0

I would say you should use the "clone" method when copying your object and then later compare as said in the php.net article.

Also a fast way would be by declaring a static method in the class that just compares the relevant "properties" like lets say "username", "password", "cookie",...

    class User
    {

    public $username;
    public $password;
    public $cookie;

    # other code

    public static function compare(&$obj1, &$obj2)
    {
    if ($obj1->username != $obj2->username)
        return 0
    if ($obj1->password != $obj2->password)
        return 0
    if ($obj1->cookie != $obj2->cookie)
        return 0
    return 1
    }


    };       

Answer 3

Simple example comparing dto class through reflection

class InvoiceDetails
{
    /** @var string */
    public $type;

    /** @var string */
    public $contractor;

    /** @var string */
    public $invoiceNumber;

    /** @var \DateTimeInterface|null */
    public $saleDate;

    /** @var \DateTimeInterface|null */
    public $issueDate;

    /** @var \DateTimeInterface|null */
    public $dueDate;

    /** @var string */
    public $payment;

    /** @var string */
    public $status;


    public function isEqual(InvoiceDetails $details): bool
    {
        $reflection = new \ReflectionClass(self::class);

        /** @var \ReflectionProperty $property */
        foreach ($reflection->getProperties() as $property) {
            $name = $property->getName();
            if ($this->$name !== $details->$name) {
                return false;
            }
        }

        return true;
    }

}

Answer 4

The only way to access the all (public, protected and private) properties of an object without modifying it is through reflection. You could, if you wanted to, clone the object before it's modified and then compare them by using the reflection functions to loop through the different properties of one of the two objects and comparing values. That would effectively tell you what properties have changed.

If all you care to see is whether or not the objects have changed, you can use the == or === operators. Have a look at the comparing objects section of PHP's documentation.

That said, wouldn't just be easier to keep track of what you've changed as you change them?