使用节点的字符串表示访问 stdClass 对象上的嵌套属性

Question

Given a variable that holds this string:

$property = 'parent->requestdata->inputs->firstname';

And an object:

$obj->parent->requestdata->inputs->firstname = 'Travis';

How do I access the value 'Travis' using the string? I tried this:

$obj->{$property}

But it looks for a property called 'parent->requestdata->inputs->firstname' not the property located at $obj->parent->requestdtaa->inputs->firstname`

I've tried various types of concatenation, use of var_export(), and others. I can explode it into an array and then loop the array like in this question .

But the variable '$property' can hold a value that goes 16 levels deep. And, the data I'm parsing can have hundreds of properties I need to import, so looping through and returning the value at each iteration until I get to level 16 X 100 items seems really inefficient; especially given that I know the actual location of the property at the start.

How do I get the value 'Travis' given (stdClass)$obj and (string)$property ?

Answer 1

My initial searches didn't yield many results, however, after thinking up a broader range of search terms I found other questions on SO that addressed similar problems. I've come up with three solutions. All will work, but not all will work for everyone.

Solution 1 - Looping

Using an approach similar to the question referenced in my original question or the loop proposed by @miken32 will work.

Solution 2 - anonymous function

The string can be exploded into an array. The array can then be parsed using array_reduce() to produce the result. In my case, the working code (with a check for incorrect/non-existent property names/spellings) was this (PHP 7+):

//create object - this comes from and external API in my case, but I'll include it here 
//so that others can copy and paste for testing purposes

$obj = (object)[
    'parent' => (object)[
        'requestdata' => (object)[
            'inputs' => (object)[
                'firstname' => 'Travis'
             ]
         ]
    ]
];

//string representing the property we want to get on the object

$property = 'parent->requestdata->inputs->firstname';

$name = array_reduce(explode('->', $property), function ($previous, $current) {
    return is_numeric($current) ? ($previous[$current] ?? null) : ($previous->$current ?? null); }, $obj);

var_dump($name); //outputs Travis

see this question for potentially relevant information and the code I based my answer on.

Solution 3 - symfony property access component

In my case, it was easy to use composer to require this component. It allows access to properties on arrays and objects using simple strings. You canread about how to use it on the symfony website. The main benefit for me over the other options was the included error checking.

My code ended up looking like this:

//create object - this comes from and external API in my case, but I'll include it here 
//so that others can copy and paste for testing purposes
//don't forget to include the component at the top of your class
//'use Symfony\Component\PropertyAccess\PropertyAccess;'

$obj = (object)[
    'parent' => (object)[
        'requestdata' => (object)[
            'inputs' => (object)[
                'firstname' => 'Travis'
             ]
         ]
    ]
];

//string representing the property we want to get on the object
//NOTE: syfony uses dot notation. I could not get standard '->' object notation to work.

$property = 'parent.requestdata.inputs.firstname';

//create symfony property access factory

$propertyAccessor = PropertyAccess::createPropertyAccessor();

//get the desired value

$name = $propertyAccessor->getValue($obj, $property);

var_dump($name); //outputs 'Travis'

All three options will work. Choose the one that works for you.

Answer 2

You're right that you'll have to do a loop iteration for each nested object, but you don't need to loop through "hundreds of properties" for each of them, you just access the one you're looking for:

$obj = (object)[
    'parent' => (object)[
        'requestdata' => (object)[
            'inputs' => (object)[
                'firstname' => 'Travis'
             ]
         ]
    ]
];
$property = "parent->requestdata->inputs->firstname";
$props = explode("->", $property);
while ($props && $obj !== null) {
    $prop = array_shift($props);
    $obj = $obj->$prop ?? null;
}
var_dump($obj);

Totally untested but seems like it should work and be fairly performant.