PHP http_build_query with two array keys that are same

Question

I want to construct this url using http_build_query:

https://www.googleapis.com/freebase/v1/topic/m/0d6lp?filter=/common/topic/notable_for&filter=/common/topic/alias

Please note that the "filter=" parameter comes twice in the url, to specify two filters.

I tried to do it this way but having a problem:

$service_url = 'https://www.googleapis.com/freebase/v1/topic';
$mid = '/m/0d6lp';
$params = array('filter' => '/common/topic/notable_for', 'filter' =>   '/common/topic/alias');
$url = $service_url . $mid . '?' . http_build_query($params);

The problem is as 'filter' array key repeats twice, only the last parameter appears in the http_build_query. How do I construct the original url with two filters?

Answer 1

The problem here of course is that every key in a PHP array (hash) can only have one value. Intrinsically, a PHP hash is not a good representation of a querystring, because the query string has an order and has no constraints about the uniqueness of the keys.

To combat this, you'll need a special querystring builder that can handle duplicate keys:

class QueryString {
    private $parts = array();

    public function add($key, $value) {
        $this->parts[] = array(
            'key'   => $key,
            'value' => $value
        );
    }

    public function build($separator = '&', $equals = '=') {
        $queryString = array();

        foreach($this->parts as $part) {
            $queryString[] = urlencode($part['key']) . $equals . urlencode($part['value']);
        }

        return implode($separator, $queryString);
    }

    public function __toString() {
        return $this->build();
    }
}

Example usage (Codepad Demo):

$qs = new QueryString();
$qs->add('filter', '1');
$qs->add('filter', '2');
var_dump($qs->build()); // filter=1&filter=2

Answer 2

I have extended @Bailey Parker's answer to handle the issue raised in the first comment to his answer. This code will create query string where one key has multiple values and both values will be preserved using []

class QueryString
{
        private $parts = array();

        public function add($key, $value) {
                if(empty($value))return;
                if(is_array($value))
                {
                        foreach ($value as $v)
                                $this->add($key,$v);
                }
                else
                {
                        $this->parts[$key][] = $value;
                }

        }

        public function build($separator = '&', $equals = '=') {
                $queryString = array();

                $parts = array();
                foreach($this->parts as $key=>$value)
                {
                        if(count($value) > 1)
                                $parts[$key] = $value;
                        else
                                $parts[$key] = $value[0];
                }
                $query = http_build_query($parts);
                return preg_replace('/%5B(?:[0-9]|[1-9][0-9]+)%5D=/', '[]=', $query);;

        }

        public function __toString() {
                return $this->build();
        }

}

this code can also accept an array of values for a particular key

$qs = new QueryString();
$qs->add('trialId', array('1','2'));
$qs->add('packageId', '12');
$qs->add('frequencyId', '4');
var_dump($qs->build());

This class will produce normal query string, with the key having multiple values added with [] sign, the output will be like this

?frequencyId=4&packageId=12&trialId[]=1&trialId[]=2

Answer 3

1. You cannot store in accoc array two or more values with one index.
2. Api does not take values like filter[]

So, I suggest you to create your own function to build that query.

Answer 4

Not the best solution, but I have a workaround:

$item = [
   'key1' => array('value1','value2'),
   'key2' => array('value3','value4')
];

$array=[
    'aaa' => 'aaa',
    'null' => 'null&'.preg_replace('/%5B(?:[0-9]|[1-9][0-9]+)%5D=/', '=', http_build_query($item,null,'&')),
    'zzz' => 'zzz'
];

echo urldecode(http_build_query($array));

Output:

aaa=aaa&null=null&key1=value1&key1=value2&key2=value3&key2=value4&zzz=zzz

WARNING: probably this won't work cause url will be:

aaa=aaa&null=null%26key1%3Dvalue1%26key1%3Dvalue2%26key2%3Dvalue3%26key2%3Dvalue4&zzz=zzz

EDIT: Other option will be preg the result before assign it to the url:

preg_replace('/%5B(?:[0-9]|[1-9][0-9]+)%5D=/', '=', http_build_query($item))

output:

key1=value1&key1=value2&key2=value3&key2=value4