PHP check whether property exists in object or cla

问题:

I understand PHP does not have a pure object variable, but I want to check whether a property is in the given object or class.

$ob = (object) array('a' => 1, 'b' => 12); 

or

$ob = new stdClass;
$ob->a = 1;
$ob->b = 2;

In JS, I can write this to check if variable a exists in an object:

if ('a' in ob)

In PHP, can anything like this be done?

Thank you very much for your advice.

回答1:

property_exists( mixed $class , string $property )

if (property_exists($ob, 'a')) 

isset( mixed $var [, mixed $... ] )

if (isset($ob->a))

isset() will return false if property is null

Example 1:

$ob->a = null
var_dump(isset($ob->a)); // false

Example 2:

class Foo
{
   public $bar = null;
}

$foo = new Foo();

var_dump(property_exists($foo, 'bar')); // true
var_dump(isset($foo->bar)); // false

回答2:

To check if the property exists and if it's null too, you can use the function property_exists().

Docs: http://php.net/manual/en/function.property-exists.php

As opposed with isset(), property_exists() returns TRUE even if the property has the value NULL.

bool property_exists ( mixed $class , string $property )

Example:

if (property_exists($testObject, $property)) {
    //do something
}

回答3:

Neither isset or property_exists work for me.

• isset returns false if the property exists but is NULL.
• property_exists returns true if the property is part of the object's class definition, even if it has been unset.

I ended up going with:

    $exists = array_key_exists($property, get_object_vars($obj));

Example:

    class Foo {
        public $bar;

        function __construct() {
            $property = 'bar';

            isset($this->$property); // FALSE
            property_exists($this, $property); // TRUE
            array_key_exists($property, get_object_vars($this)); // TRUE

            unset($this->$property);

            isset($this->$property); // FALSE
            property_exists($this, $property); // TRUE
            array_key_exists($property, get_object_vars($this)); // FALSE

            $this->$property = 'baz';

            isset($this->$property); // TRUE
            property_exists($this, $property); // TRUE
            array_key_exists($property, get_object_vars($this));  // TRUE
        }
    }

回答4:

If you want to know if a property exists in an instance of a class that you have defined, simply combine property_exists() with isset().

public function hasProperty($property)
{
    return property_exists($this, $property) && isset($this->$property);
}

回答5:

To check if something exits, you can use the PHP function isset() see php.net. This function will check if the variable is set and is not NULL.

Example:

if(isset($obj->a))
{ 
  //do something
}

If you need to check if a property exists in a class, then you can use the build in function property_exists()

Example:

if (property_exists('class', $property)) {
    //do something
}