Retrieving Properties Dynamically

[LostInTheWoods]

Hi,

 

I need a little help with retrieving properties from an object, but having the name of the property passed in to a function. Er code might help explain...

 

Here 'version'is the name of the object property I am trying to retrieve:

 

// Property name hard coded in function
function myFunction1($object){

  print($object->version);

}

// Property passed in as a parameter.
function myFunction2($object, $propertyName){

  print($object->$propertyName);     // Wrong!
  
  print($object->[$propertyName]);   // Wrong!
  
  print($object->[propertyName]);    // Wrong!

}

 

So how can I retrieve an object's property by it's name, but dynamically?

 

Many Thanks,

Stephen

[jcrocker]

Hi, I might be mistaken, but I believe you can do exactly what you want, and you was correct on how to do it, not sure why it didn't work! I have given the code below for what I believe you are trying to do:

 

class test
{
public $version;
public function __construct()
{
	$this->version = 5;
}
}

function getproperty(test $object, $property)
{
echo $object->$property;
}

$foo = new test();
getproperty($foo, 'version');

 

One thing you might want to check on your code is the scope of the property you are trying to access (it must be public and defined as such).

 

 

[LostInTheWoods]

Hi,

 

This is weird, I have tried your example code and it works fine. The complete scenario of what I am trying to do is of course more complicated than I gave in my first example, but I can't see why this weird behaviour is happening. Here is the bigger picture:

 

I am retrieving an array of result objects from a query and I am trying to write a function that will retrieve the properties of all the objects. So I am looping over the array and then using the properties from each result object. In an attempt to make the function more generic, I thought passing in a property name would be useful. I do a check before trying to retrieve a property to see that it exists, and it does:

 

if(property_exists($result, $value) && property_exists($result, $display)){
print("<option value=\"$result->$value\" >$result->$display</option>");
}

 

but this outputs '->$display' in the select options. And I also get the PHP error:

 

"Object of class stdClass could not be converted to string"

 

What is the obvious thing I am missing here?

 

Thanks,

Stephen

[jcrocker]

Hi, I think it is how you are outputting, PHP can be very unusual at times, try this instead:

 

if(property_exists($result, $value) && property_exists($result, $display))
{
print('<option value="' . $result->$value . '" >' . $result->$display '</option>');
}

 

Also you should consider using get and set to return false when the property of an object doesn't exist (just ensures you wont get a fatal error).

 

On a side note, use echo instead of print (it's slightly faster)!

 

 

[keeB]

Don't mix in HTML this way. It's always a bad idea and makes your code much more confusing to read.

 

<?php

class A {
   public $a = "1";
   public $b = "2";
}

$result = new A();
$value = a;
$display = b;

print_r( $ret =array($result->$value, $result->$display));

print '<option value="' . $ret[0] . '">' . $ret[1] . '</option>';
?>

 

[LostInTheWoods]

Thanks Guys!

 

I normally do use echo, and I now have a good reason to continue doing so more consistently. I don't understand your point keeB. You have placed the property values into an array instead of using them directly. What is the advantage of this?

 

Thanks,

Stephen

[keeB]

The advantage is separating logic from presentation.

 

In this example, I would wrap that tidbit in a function and return the array.

 

A procedural approach

<?php

//some-include-file.inc.php

function get_option($obj, $value, $display) {
    return array($obj->$value, $obj->$display);
}

//some-display-file.php
$result = new SomeObject();
$ret = get_option($result, $value, $display);
print '<option value="' . $ret[0] . '">' . $ret[1] . '</option>';

 

An OO approach would be harder to template for you without more detail.