July 7, 2006
Updating ’select’ controls with AJAX
In web design there are frequently times when a form needs to be able to have the contents of ’select control B’ depend on the contents of ’select control A’ (or some other control type for that matter). Using conventional web design methods, one would have to define a ‘onChange’ javascript event for ’select control A’, which fires off a callback that updates the second select control.
This is cumbersome to code, and it leads to upleasant page refreshes every time the user changes the value of ’select control A’.
Another way to handle this is by using AJAX methods to update the second control as needed. This is fairly easy in Rails, and is even easier if you make use of the KRJS plugin (http://www.agilewebdevelopment.com/plugins/krjs).
-
# View
-
<%= select ‘model’,'id’, Model.find(:all).map {|x| [x.name, x.id]} %>
-
<div id=’select-b’>
-
<%= select ‘model’,'category_id’, Model.find(@model.id).categories.map {|x| [x.name, x.id]} %>
-
</div>
In this example, the second select (’select-b’) is normally populated with ‘categories’ associated with the initially selected model. Changing the model would not normally update the second select, so things would be all wrong.
-
# Controller
-
def on_model_id_change
-
render :update do |page|
-
@categories = Model.find(params[:dom_value]).categories
-
page.replace_html ’select-b’, :inline=>"<%= select ‘model’,'category_id’, @categories.map {|o| [o.name, o.id]} %>"
-
end
-
end
This is probably the easiest way to update a select box using AJAX. Remember, this only works with the KRJS plugin.
UPDATE: Of course all of this only works if you have AJAX enabled by adding <%= javascript_include_tag :defaults %> in the
of your layout file.
Filed by Kevin Olbrich at 12:27 pm under Ruby on Rails, User Interface, select controls
39 Comments
Kevin,
This looks nice and simple, but will it work when there is nesting of more than one dependent select? ie. If there are three, select the first one, the second one updates. But then if you change the second, will the third now update? When I’ve tried an approach like this, the observer related to the second select box has dissapeared and so doesn’t update the third box. I don’t have any experience with the KRJS plugin. If this works it might be time to start really having a look ;)
Good question, I’ll have to try it.
I tried doing second select control and setting up a second controller action to see if work as expected. I was pleasantly surprised to discover that the second select works just fine, even if it has been replaced itself. I’ve only tested this in Firefox, but I suspect it will work fine elsewhere.
I have installed ROR on Win-XP. as part of my learning process after having gone thro recipe cookbook, I thought i will try some expts. so I have 2 list boxes – first one is category and the latter is recipe. I want to have the recipes in 2nd list box depending on the category selected in the first one. While googling I came to this page.
First I installed KRJS – but when I tried the sample I got an error cannot access cattr_… May be I will try again starting the webrick server again.
Secondly can some one explain above example code in terms recipe_categories and recipe – please
Thanks in advance
Make sure that you have a line like this in your \layout\application.rhtml file.
or AJAX won’t work for you.
You will need to restart Webrick anytime you install a plugin.
That should work so long as your Recipe belongs_to a Category
[...] If you have a ‘Really Long List’ to select from, then using a cascading select makes a lot of sense (unless you want your users to hate you). The problem is that they are a pain to code (well, not so bad if you use the KRJS plugin ), and they are still a pain to use if you actually know what you are looking for (then you have to remember what ‘category’ if falls in). [...]
Kevin,
I am new to ROR and going through the tutorials in the Agile Web Development with Rails book. I was trying out your plugin with 3 select boxes. It works great for the first 2 select boxes, but I can’t seem to get the 3rd one to update. Basically Product belongs_to Listing and Listing belongs_to Category. Please advise…
Thanks
Richard
I had the same problem until I wrote the observer for select2 within the partial2. Now I have a cascaded selection… is it your case ?
How do you use this plugin with the Date Helper select fields? I am already clear that it is too hard to use date_select because this generates three select fields which would each need their own method on_…. My question is, how does KRJS know how which select field your talking about if you use the select_month, select_day, or select_year methods to create the tag, because they don’t accept ‘object’, ‘method’, which it seems is what KRJS is using to identify which select to apply the actionlistner to. ???
Sam
Yes, I don’t think KRJS works well with date_selects or datetime_selects. The helpers also don’t apply an html id, which would be required to be able to access them via AJAX. In these cases, it might be better to use ‘observe_form’.
[...] Aqui teneis un ejemplo, blog de ScrWerks [...]
Thanks for this! I spent ages searching through lots of forums and wikis where other people had been asking the same thing without getting a simple answer, but I got this up and running within 20 minutes.
I am almost there, but how is params[:dom_value] getting set and where in the above example?
In mycase, that is not getting set?
Any help is greatly appreciated.
I’ve tried to put this code into my application and couldn’t get it to work. Even when I create a new app with just the two sample tables in the example it doesn’t work.
I’ve tried replicating this exact piece of code mentioned above but I cannot get it to work. I’m a rails and even a programming newbiew so forgive me for asking something that my sound stupid.
I keep getting a “undefined local variable or method `category’ for #:0×3295380>’
which is getting frustrating since this a is piece that I must get up and running in my website. In my application I have simulations which consist of rules. I need to get the app to load the correct rules when selected. In the rules I have (among others) two colums with the second dependend on the first. One with carrier and the other with the carriers products.
Any ideas?
Bas,
You need to replace ‘categories’ with whatever is appropriate for your application. The example above assumes that the Model class has_many :categories.
Kevin,
Thanks, I finally got it to work. For the benefit of other newbies let me try to explain my mistakes with trying to get this up and running. I had to change some single quotes into double quotes (which I don’t understand).
Second was ( and this took ages to figure out) the x.name = the column name of column whose values you want to display).
Thanks, it has been very helpful and a great learning experience
hey kevin
i tried this code but there was some problem…i am new to rails so could you please help me out.whenever i put the and start the server nothing is displayed on the screen… this is wat i did
controller::::
class AdminController “”
end
end
def index
@state = State.find(1)
end
end
index.rhtml::::
layouts/application.rhtml
i have also installed krjs plugin and i am using mongrel server
i had given “” this is layouts
javascript_include_tag :defaults
i had given that javascript include tag in layouts and never gave any output on the screen
hey i got that like i just removed of the layout and put off the same thing in index.rhml it self…but one thing that code is really good
Hello:
Thank you for posting this tutorial. It’s exactly what I’ve been looking for. Unfortunately, being new to rails, I’ve come across a bit of trouble coding this in. I’ve installed the plugin, defined model relations, enabled ajax as instructed in views/layouts/viewname.rhtml and have been going over every bit of my view and controller code for hours. All seems to be in line. However, I keep getting a runtime error stating “Called id for nil, which would mistakenly be 4 –” when trying to load the view. Any idea what could be mucking it up?
Thanks,
Peter
I messed around with my controller code, but I have a new error. To use the category/recipe example above, I get an error on line 4 of show.rhtml that says “Couldn’t find Category without an ID”. If you have any ideas on what could be causing this, I’d love to know.
Thanks,
Peter
your @model instance variable needs to be intialized with some reasonable default.
I followed this example and I’m able to display the view correctly. However, when I change the ‘country’ dropdown I get this error in Firefox:
RJS error: TypeError: $(element) has no properties.
Then I click OK and get another pop up with this message:
Element.update(”state”, “”);
Nicolas, you need to make sure that the id on the second select is the same as the one you try to update in the ajax response. Otherwise you get this JS error. FYI, Firebug is a great way to debug AJAX actions.
When I change the country select it correctly sends the correct country_id through the dom_value and queries the list of states in my “on_country_id_change” function in my controller. I use “puts” to see the output. The “page.replace_html” command is the one that gives me the error. Everything works fine when I load the page. Both country and state selects are filled correctly.
Here is my function:
def on_country_id_change
render :update do |page|
@states = Country.find(params[:dom_value]).states
page.replace_html ’state’, :inline => “”
end
end
Here is my HTML
‘name ASC’).map {|x| [x.name, x.id]} %>
Here is the error from Firebug:
try {
Element.update(”state”, “England\nNorthern Ireland\nScotland\nWales\nBritish Virgin Islands”);
} catch (e) { alert(’RJS error:\n\n’ + e.toString()); alert(’Element.update(\”state\”, \”England\\nNorthern Ireland\\nScotland\\nWales\\nBritish Virgin Islands\”);’); throw e }
I hope you can help me out here.
Thanks,
My code is not being displayed correctly in this thread. How do you make it display correctly ?
try using
{square bracket}code lang=”ruby”{square bracket}
{square bracket}/code{square bracket}
around your code.
If you are trying to update the inner html of a select, don’t. It doens’t work well. Just replace the entire select control.
Kevin, here is my code:
Do you see anything wrong with this code ?
My “state” table has a “country_id” column
Thanks for your help!
Mmm.. How can I show html code ? I tried with lang=”html” but it did not work apparently.
Try the “ruby” code, it will just syntax hilight it wrong.
if your HTML page has a table with an ‘id’ of ’state’, it will replace the entire table with the contents of the inline template.. I would probably suggest using a partial to render the table, then you can just re-render it and send it back as the response.
Here is the HTML I use:
I’m just wondering what I’m doing different than this example ? I just tried to replace “categories” with “countries” and “recipes” with “states”.
I use prototype 1.5.0.
Nick,
It’s still not showing the right HTML. I just tried to copy this example.
Well there appears to be some bug with the KRJS or i am doing something terribly wrong?? While the code for the view is working perfectly, and displaying the dropdown menus, when installing the KRJS plugin (starting and restarting the server) the following error message appears: “wrong number of arguments” for the first
Any insight?
….select menu that was, but i didnt escape the ruby tags…..
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