How to pass an array within a query string?

Question 1

Is there a standard way of passing an array through a query string?

To be clear, I have a query string with multiple values, one of which would be an array value. I want that query string value to be treated as an array- I don't want the array to be exploded so that it is indistinguishable from the other query string variables.

Also, according to this post answer, the author suggests that query string support for arrays is not defined. Is this accurate?

EDIT:

Based on @Alex's answer, there is no standard way of doing this, so my follow up is then what is an easy way to recognize that the paramater I'm reading is an array in both PHP and Javascript?

Would it be acceptable to name multiple params the same name, and that way I would know that they belong to an array? Example:

?myarray=value1&myarray=value2&myarray=value3...

Or would this be bad practice?

Question 2

Here's what I figured out:

Submitting multi-value form fields, i.e. submitting arrays through GET/POST vars, can be done several different ways, as a standard is not necessarily spelled out.

Three possible ways to send multi-value fields or arrays would be:

?cars[]=Saab&cars[]=Audi (Best way- PHP reads this into an array)
?cars=Saab&cars=Audi (Bad way- PHP will only register last value)
?cars=Saab,Audi (Haven't tried this)

Form Examples

On a form, multi-valued fields could take the form of a select box set to multiple:

<form> 
    <select multiple="multiple" name="cars[]"> 
        <option>Volvo</option> 
        <option>Saab</option> 
        <option>Mercedes</option> 
    </select>
</form>

(NOTE: In this case, it would be important to name the select control some_name[], so that the resulting request vars would be registered as an array by PHP)

... or as multiple hidden fields with the same name:

<input type="hidden" name="cars[]" value="Volvo">
<input type="hidden" name="cars[]" value="Saab">
<input type="hidden" name="cars[]" value="Mercedes">

NOTE: Using field[] for multiple values is really poorly documented. I don't see any mention of it in the section on multi-valued keys in Query string - Wikipedia, or in the W3C docs dealing with multi-select inputs.

UPDATE

As commenters have pointed out, this is very much framework-specific. Some examples:

Query string:

?list_a=1&list_a=2&list_a=3&list_b[]=1&list_b[]=2&list_b[]=3&list_c=1,2,3

Rails:

"list_a": "3", 
"list_b":[
    "1",
    "2",
    "3"
  ], 
"list_c": "1,2,3"

Angular:

 "list_a": [
    "1",
    "2",
    "3"
  ],
  "list_b[]": [
    "1",
    "2",
    "3"
  ],
  "list_c": "1,2,3"

(Angular discussion)

See comments for examples in node.js, Wordpress, ASP.net

Maintaining order: One more thing to consider is that if you need to maintain the order of your items (i.e. array as an ordered list), you really only have one option, which is passing a delimited list of values, and explicitly converting it to an array yourself.

Question 3

Basically, you just need to use PHP's implode function to turn an array into a comma-separated list. i.e. for the $item array:

$item = array('item1', 'item2');
echo implode(',', $item);

Will output:

item1,item2

So, something like this should print a querystring similar to what you want:

echo 'pname='.implode(',', $pname).
     '&item='.implode(',', $item).
     '&qty='.implode(',', $qty);

Question 4

You need to use JSON.stringify to first serialize your object to JSON, and then specify the contentType so your server understands it's JSON. This should do the trick:

$.ajax({
    url: url,
    type: "POST",
    data: JSON.stringify(data),
    contentType: "application/json",
    complete: callback
});

Note that the JSON object is natively available in browsers that support JavaScript 1.7 / ECMAScript 5 or later. If you need legacy support you can use json2.

Question 5

Per http://tools.ietf.org/html/rfc3986

In section 2.2 Reserved Characters, the following characters are listed:

reserved = gen-delims / sub-delims

gen-delims = “:” / “/” / “?” / “#” / “[” / “]” / “@”

sub-delims = “!” / “$” / “&” / “’” / “(” / “)” / “*” / “+” / “,” / “;” / “=”

The spec then says:

If data for a URI component would conflict with a reserved character’s purpose as a delimiter, then the conflicting data must be percent-encoded before the URI is formed.

Next, in section 2.3 Unreserved Characters, the following are listed:

unreserved = ALPHA / DIGIT / “-” / “.” / “_” / “~”

Question 6

Your query string should rather look like this:

?formparts[]=a&formparts[]=b&formparts[]=c

How to pass an array within a query string?

Answers

Form Examples

php,arrays,query-string,querystringparameter