Utilize a stored string as the destination for the content of an object

Question

Utilize a stored string as the destination for the content of an object

We are currently working on processing a large amount of json data and trying to specify which parts of it to use using string variables.

My goal is to convert a string into an object path to access the content of an item.

The following code works correctly:

<?php 
$pmdd_ds_json_obj = json_decode($pmdd_ds_json_data);
echo $pmdd_ds_json_obj[0]->title->rendered; // displays "Wisconsin Investment Board"
?>

However, I am unable to achieve the same outcome with the code below:

$num = 0;
$root =  "pmdd_ds_json_obj[$num]->";
$content = "title->rendered"
$obj_content = ${$root.$content};

// I have also tried different approaches.
echo $root.$content;
echo ${$root.$content};
echo ${"$root.$content"};

Is what I'm attempting even possible? I have attempted numerous variations and would appreciate a fresh perspective!

json data

[{
    "date": "2019-07-04T10:21:15",
    "title": {
        "rendered": "Wisconsin Investment Board"
    },
    "_links": {
        "self": [{
            "href": "https:\/\/refi.global\/europe\/wp-json\/wp\/v2\/posts\/309891"
        }]
    }
}]

php json

Answer 1

Answer №1

Using dynamic variables will not work with array keys or arrow operators as you've attempted. While you could achieve this using eval(), it is not recommended.

Instead, consider using the json_decode function with a flag set to return an associative array instead of stdClass objects. More information can be found at this link.

$foo = json_decode($json, true);

To access the desired value, you can create a function that resolves array values by dot notation and store it in a variable. Refer to this answer for more details: here.

<?php

$json = '[{
    "date": "2019-07-04T10:21:15",
    "title": {
        "rendered": "Wisconsin Investment Board"
    }
}]';

// decode as an associative array
$pmdd_ds_json_obj = json_decode($json, true);

/**
 * @link https://stackoverflow.com/a/14706302/2286736
 */
function resolve(array $a, $path, $default = null) {
    $current = $a;
    $p = strtok($path, '.');

    while ($p !== false) {
        if (!isset($current[$p])) {
            return $default;
        }
        $current = $current[$p];
        $p = strtok('.');
    }

    return $current;
}

// key variable
$key = '0.title.rendered';

// value can be resolved by the dot notation path
$value = resolve($pmdd_ds_json_obj, $key);
var_dump($value); // Wisconsin Investment Board

Further modifications to the resolve() function allow it to accept objects as inputs:

$json = '[{
    "date": "2019-07-04T10:21:15",
    "title": {
        "rendered": "Wisconsin Investment Board"
    },
    "_links": {
        "self": [{
            "href": "https:\/\/refi.global\/europe\/wp-json\/wp\/v2\/posts\/309891"
        }]
    }
}]';

// decode without specifying return type (using stdClass)
$pmdd_ds_json_obj = json_decode($json);

function resolve($a, $path, $default = null) {
    $current = $a;
    $p = strtok($path, '.');

    while ($p !== false) {
        if (
            (is_array($current) && !isset($current[$p]))
            || (is_object($current) && !isset($current->$p))
        ) {
            return $default;
        }
        $current = is_array($current) ? $current[$p] : $current->$p;
        $p = strtok('.');
    }

    return $current;
}

// key variable
$key = '0._links.self.0.href';

// value can be resolved by the dot notation path
$value = resolve($pmdd_ds_json_obj, $key);

Answer 2

Using dynamic variables will not work with array keys or arrow operators as you've attempted. While you could achieve this using eval(), it is not recommended.

Instead, consider using the json_decode function with a flag set to return an associative array instead of stdClass objects. More information can be found at this link.

$foo = json_decode($json, true);

To access the desired value, you can create a function that resolves array values by dot notation and store it in a variable. Refer to this answer for more details: here.

<?php

$json = '[{
    "date": "2019-07-04T10:21:15",
    "title": {
        "rendered": "Wisconsin Investment Board"
    }
}]';

// decode as an associative array
$pmdd_ds_json_obj = json_decode($json, true);

/**
 * @link https://stackoverflow.com/a/14706302/2286736
 */
function resolve(array $a, $path, $default = null) {
    $current = $a;
    $p = strtok($path, '.');

    while ($p !== false) {
        if (!isset($current[$p])) {
            return $default;
        }
        $current = $current[$p];
        $p = strtok('.');
    }

    return $current;
}

// key variable
$key = '0.title.rendered';

// value can be resolved by the dot notation path
$value = resolve($pmdd_ds_json_obj, $key);
var_dump($value); // Wisconsin Investment Board

Further modifications to the resolve() function allow it to accept objects as inputs:

$json = '[{
    "date": "2019-07-04T10:21:15",
    "title": {
        "rendered": "Wisconsin Investment Board"
    },
    "_links": {
        "self": [{
            "href": "https:\/\/refi.global\/europe\/wp-json\/wp\/v2\/posts\/309891"
        }]
    }
}]';

// decode without specifying return type (using stdClass)
$pmdd_ds_json_obj = json_decode($json);

function resolve($a, $path, $default = null) {
    $current = $a;
    $p = strtok($path, '.');

    while ($p !== false) {
        if (
            (is_array($current) && !isset($current[$p]))
            || (is_object($current) && !isset($current->$p))
        ) {
            return $default;
        }
        $current = is_array($current) ? $current[$p] : $current->$p;
        $p = strtok('.');
    }

    return $current;
}

// key variable
$key = '0._links.self.0.href';

// value can be resolved by the dot notation path
$value = resolve($pmdd_ds_json_obj, $key);

Utilize a stored string as the destination for the content of an object

json data

Answer №1

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