Dependency drop down list

Rails
1

Hello,

 I am trying load a drop down list based on selection from first

drop
down list. Based on first drop down list selection, I am able to fetch
data for second drop down list but I am not able to refresh second
dropdown list contents.

How Can I refresh second drop list on selection of first drop down list,
I have values for drop down list in an array.

2

You’d need to do this in Javascript using what’s called a “chained
select”.
There’s a variety of plugins that do this, but here’s
one: Chained selects

You typically have two options:

  1. Write out all of the available options for your second select when
    the page loads, then selectively hide/show some of them depending on
    the
    first select’s selection.
  2. Make an ajax call back to your application when the first select
    is
    changed which will return to you the available options to populate
    the
    second select. This may be the best option if you have a lot of
    options in
    your selects.

If you need to support clients that do not have javascript enabled: I’ve
also seen option #1 done with optgroups, so you’d write out your second
select with the corresponding options for each option in the first
select
nested within optgroups. You’d then selectively hide/show the options
depending on what’s selected from the first select. The advantage here
is
that when JS is not available, the user just needs to scroll through the
second select to find the options that correspond to their selection
from
the first select. It’s not ideal, but it’s a reasonable fallback.

Jim

3

On Mar 5, 2014, at 1:35 PM, [email protected] wrote:

You’d need to do this in Javascript using what’s called a “chained select”.
There’s a variety of plugins that do this, but here’s one:
Chained selects

You typically have two options:

  • Write out all of the available options for your second select when the page
    loads, then selectively hide/show some of them depending on the first select’s
    selection.
  • Make an ajax call back to your application when the first select is changed
    which will return to you the available options to populate the second select.
    This may be the best option if you have a lot of options in your selects.
    If you need to support clients that do not have javascript enabled: I’ve also
    seen option #1 done with optgroups, so you’d write out your second select with the
    corresponding options for each option in the first select nested within optgroups.
    You’d then selectively hide/show the options depending on what’s selected from the
    first select. The advantage here is that when JS is not available, the user just
    needs to scroll through the second select to find the options that correspond to
    their selection from the first select. It’s not ideal, but it’s a reasonable
    fallback.

And I just want to add (just answered a couple questions in a row about
this on SO) that you should not rely on stuffing HTML into the
tag to alter its options. This will work in a couple of browsers:

document.getElementById(‘my_picker’).innerHTML = ‘Whatever’;

but it will fail silently and weirdly in several others. The best way to
build up a picker from an Ajax response is to get a JSON (or other
array) of value/text pairs and build up the option elements inside a
loop:

myJSON.each(function(elm){
my_picker.options[my_picker.options.length] = new Option(
elm[‘text’], elm[‘value’] );
});

Hope this helps,

Walter