HTML Form: POST an array of objects

Question

Submitting a class roster. Adding 3 students at once. Each student has first, last, age.

Question: How can we get all of the students in an array of arrays?

students[0] => Array (   ["first"] => "first name for 0",   ["last"] => "last name for 0",   ["age"] => "age for 0" ), students[1] => Array (   ["first"] => "first name for 1",   ["last"] => "last name for 1",   ["age"] => "age for 1" ),  ...   

Details
For one student:

<input type="text" name="first">   <input type="text" name="last">   <input type="text" name="age">   

We can return multiple students in separate arrays like this:

<input type="text" name="students[first][]">   <input type="text" name="students[last][]">   <input type="text" name="students[age][]">   

which returns an array of firsts, lasts and ages

students["first"] = [array of first names] students["last"] = [array of last names] students["age"] = [array of ages]   

Theoretically we can get all the info for a student by accessing the same index (say "3" for each array).

We do not want to programatically add an index in the form.
Do not want:

<input type="text" name="students[hardcoded_index][first]">   <input type="text" name="students[hardcoded_index][last]">   <input type="text" name="students[hardcoded_index][age]">   

If for any reason it matters, we are using Rails for views but can use form helpers or HTML.

Answer 1

tl;dr: Add empty brackets ([]) after students to the input names.

Fiddling with Rack::Utils.parse_nested_query it seems you can get the payload you want like this:

<!-- first student --> <input type="text" name="students[][first]"> <input type="text" name="students[][last]"> <input type="text" name="students[][age]">  <!-- second student --> <input type="text" name="students[][first]"> <input type="text" name="students[][last]"> <input type="text" name="students[][age]"> 

Note the empty brackets ([]) after students. This tells Rack you want the students param to be an array. Subsequent params encountered (with the same name) will start a new element.

POST /myroute?students[][first]=foo&students[][last]=bar&students[][age]=21&students[][first]=baz&students[][last]=qux&students[][age]=19

Gets parsed like this:

{"students" => [   {     "first" => "foo",      "last" => "bar",       "age" => "21"   },   {     "first" => "baz",      "last" => "qux",       "age" => "19"   } ]} 

Further reading: http://codefol.io/posts/How-Does-Rack-Parse-Query-Params-With-parse-nested-query