Skip to main content

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.





Code
<form>
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>
</form>


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

"fruit=apple&fruit=orange&fruit=banana"

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 "[]"

Code
<form>
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>
</form>


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).

Comments

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 ?

Popular posts from this blog

Freezing Gems

What is a gem and why would you want to freeze it? In Ruby, there are times when you want to access pieces of functionality that other people of written (3rd party libraries) and you normally have 2 options. You can install a plug in or install a gem. Normally the method you use is determined by which ever is made available by the author. Gems are installed on the host machine and are pretty handy when you want to run things in the command line or else across lots of projects, but their downside is that if you use a gem in a Rails project there is no automatic publishing mechanism when you deploy your site. You will need to log onto the remote host machine and install the gem manually. Plugins are specific to Rails and are similar to gems in that they are also 3rd party libraries. However they are associated with your Rails project as opposed to your machine so they will get posted to the server on a regular deploy. Freezing a gem is the process of transforming a gem into a plug in

Unit/Functional Testing RubyAMF

One of my current projects is using RubyAMF to communicate with Flash (http://rubyforge.org/projects/rubyamf/). On the whole this is really nice because it allows you to transfer Ruby objects directly to ActionScript ones (as opposed to translating the object into XML, sending the XML and then recreating the object in ActionScript). However, Rails does not provide a built in transport mechanism for AMF, so we cannot run functional testing directly on the data call (as we could for an XML or HTML transport layer). This is a show stopper for a lot of people (Rails w/o Unit testing = a big mess of trouble when something goes wrong). We can though serve both the HTML and the AMF formats depending on the request format. This means that we can test the object instantiation logic and make sure there are no errors in the controllers (though we cannot check the actual format of the data being served). In the controller, instead of rendering AMF alone, do the following respond_to do |format|

Responsive Web Design

I wanted to go over Responsive Web Design using CSS. In the old days of web development, we had to code to common screen sizes (i.e. 800 X 600, 1024 X 768) and we patiently waited for people to upgrade their computers to have a decent amount of screen real estate so we could design things the way we really wanted. We also took on semi stretchy web layouts etc to expand and contract appropriately. Then about 2 or 3 years ago, Apple released this little device called an iPhone with a 320 X 480 resolution which took the world by storm and suddenly a lot of people were viewing your website on a tiny screen again... Anyways, as it can be difficult to design a site which looks good on 320 X 480 AND 1680 X 1050, we need to come up with some kind of solution. One way is to sniff the client and then use an appropriate stylesheet, but then you are mixing CSS with either JavaScript or server side programming and also potentially maintaining a list of appropriate clients and stylesheets. Also,