Best approach to add form elements dynamically

Rails
1

I am struggling with how to add dynamically add form elements to a form
based on user action. Now here is my situation:
I have model Project that has_many line_items
On the form to create a project I initially display form elements (some
drop downs and text boxes) for adding just one line_item. There is also
a button or a link on the page (not sure if this should be in the main
form or outside). One the user selects that button/link I need to add
another set form elements to add another line_item and this can continue
to add more line items. It would be nice to provide another button/link
to delete line_items. After the user all the form elements for the
project and line_items, they can submit the form that will save the
project and line_items.

So far I have tried to use RJS to add a new line item. But seems like I
have to keep a tab of line_items added so far so that name for elements
for line_items like line_item1, line_item2 etc. So I have to pass each
time to the RJS call that can generate approriate form elememts and also
increment the line_item count. I was hoping to set a hidden element
containing the line_item count and use rjs replace that hidden element
every time the user adds a line_item.

This seems a little kludgy to me and I was wondering if somebody can
suggest a better approach or I am better off sending the whole form to
the server and based name of button pressed either the save the project
or redisplay the new project page by adding a new line_item.

2

I can’t say whether this is the “best” way, but it’s my way. I use
observe_form on a radio button and have it call my own JavaScript
instead of
making an AJAX call. There are a few of my helpers, so don’t worry about
those. Here’s an example of the code:

<%= start_form_tag(nil, {:id => ‘lien_holder’, :name => ‘lien_holder’})
%>
<%= observe_form(:lien_holder, :frequency => 0.5, :function =>
“revealDetail();”) %>



<%= form_rows_from_collection([
[‘*action’, radios_from_collection(:change_lien_holder, :user_action,
[‘add’, ‘change’, ‘delete’])],
[‘*effective date’, dynarch_date_select(‘change_lien_holder’,
‘effective_date’)],
]) %>
Change Lien Holder



<%= form_rows_from_collection([
[‘*bank name’, text_field(:change_lien_holder, :bank_name)],
[‘*address’, text_field(:change_lien_holder, :address1)],
[‘address’, text_field(:change_lien_holder, :address2)],
[‘*city’, text_field(:change_lien_holder, :city)],
[‘*state’, select_from_hash(:change_lien_holder, :state,
@state_hash, :sorted => true)],
[‘*zip’, text_field(:change_lien_holder, :zip)],
]) %>


<%= submit_link ‘send changes’ %>
<%= end_form_tag %>

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3

Steve,

That seems to be the solution to hide or show some form elements
(fixed) based on some selection. It does not see to add for elements
dynamically. Correct me if I am wrong?

Steve R. wrote:

I can’t say whether this is the “best” way, but it’s my way. I use
observe_form on a radio button and have it call my own JavaScript
instead of
making an AJAX call. There are a few of my helpers, so don’t worry about
those. Here’s an example of the code:

… rest of message deleted

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4

Correct. It presumes you have knowledge of what the possible fields are
at
the point where you construct the original form. My presumption is that
the
superset of all form fields is bounded by the attributes of my AR model,
and
the widgets that may control visibility.

If you really want to add form elements dynamically, RJS is your best
bet.
You can simply stick new stuff in divs on your page. E.g.,

controller_name.rb

def add_a_field
@my_new_field = “Enter gibberish: #{text_field_tag(‘whoa! a new edit
box’)}”
end

controller_name.rjs

page.insert_html :bottom, ‘new_content_div’, @my_new_field

Whatever you know is going to be there.

Give it a try. This kind of thing takes some messing around to get
right.

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