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Checkbox arrays in Rails

Rails has got some nice default form options available in the FormHelper, however the check_box still leaves a little to be desired. It's great if you have one or two disparate elements, but what about when you want people to choose from a list of items like the following?

Choose your favorite fruits.

Choose your favorite fruits.
<div><input value="apple" id="apple" name="fruit" type="checkbox"><label for="apple">Apple</label></div>
<div><input value="orange" id="orange" name="fruit" type="checkbox"><label for="orange">Orange</label></div>
<div><input value="banana" id="banana" name="fruit" type="checkbox"><label for="banana">Banana</label></div>

In the example above, they all have the name fruit which means that if you choose all of them and submit them to the server, you will get the parameter string


All well and good, except when you are in the controller and you try and get the value of fruit (params[:fruit]), you will not get an array with the values of ["apple", "orange", "banana"]. You will only get "banana".

I like bananas as much as the next guy, but I want all the fruit...

So how do you do this?

It appears you have to explicitly tell Rails that it is an array. You can do this by using the square brackets "[]"

Choose your favorite fruits.
<div><input value="apple" id="apple" name="fruit[]" type="checkbox"><label for="apple">Apple</label></div>
<div><input value="orange" id="orange" name="fruit[]" type="checkbox"><label for="orange">Orange</label></div>
<div><input value="banana" id="banana" name="fruit[]" type="checkbox"><label for="banana">Banana</label></div>

Now when you call params[:fruit], you will get the array ["apple", "orange", "banana"].

Note that this will work with any other type of elements as well (as long as there is a [] directive to turn them into an array).


Eric said…
Great post. You saved me a lot of time trying to figure this out. Thanks!
Anonymous said…
Thanks man!
I had the same problem and this helped me solve it fast.

One thing to note, you can't use a symbol for the name when doing this. You have to use quotes.
check_box_tag :fruit[] won't work while
check_box_tag "fruit[]" will.
Anonymous said…
Important point here: check_box_tag, as its first argument, takes a name. HOWEVER, what it really does is set both id and name equal to a cleaned version of your input. So say you put in "Bob[]". For some reason, check_box_tag parses this out at "bob_", which obviously doesn't work with this array concept. What you need to do is add the options array at the end with the argument :name => "Bob[]". That sets it properly.
Anonymous said…
Small addendum to the above: the HMABTM association is supposed to autocreate some sort of association between your model objects in such a way as to be able to pass an argument like "obj1[obj2_ids][]" to check_box_tag, but it doesn't seem to work for me. This will give you something of a workaround, though remember that you must parse out this checkbox array manually in your controller (it will not be done automagically as in the HMABTM example)
Anonymous said…
Спасибо за помощь!
Anonymous said…
Интересно, но все же хотелось бы побольше узнать об этом. Понравилась статья!:-)
Anonymous said…
Увлекательно. Хотелось бы еще выслушать мнение специалистов по этому поводу :)
Alex said…
Thanks! In PHP, you can get the info from the generated HTTPRequest with some code like:

$fruits = $_POST["fruit"];

for ($i=0; $i";
Anonymous said…
Гена лютый кот с усами! :-)
Anonymous said…
How would you assign the string obtained to a field in the database?
Keep up the good work.
Anonymous said…
How can I do the same with f.check_box ?

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