54

I'm trying to pass an array into a hidden_field.

The following User has 3 roles [2,4,5]

>> u = User.find_by_login("lesa")
=> #<User id: 5, login: "lesa", email: "[email protected]", crypted_password: "0f2776e68f1054a2678ad69a3b28e35ad9f42078", salt: "f02ef9e00d16f1b9f82dfcc488fdf96bf5aab4a8", created_at: "2009-12-29 15:15:51", updated_at: "2010-01-06 06:27:16", remember_token: nil, remember_token_expires_at: nil>
>> u.roles.map(&:id)
=> [2, 4, 5]

Users/edit.html.erb

<% form_for @user do |f| -%>
<%= f.hidden_field :role_ids, :value => @user.roles.map(&:id) %>

When I submit my edit form, I receive an error: ActiveRecord::RecordNotFound in UsersController#update "Couldn't find Role with ID=245"

How can I pass an array into the hidden_field?

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7 Answers 7

Reset to default
128

I would use this technique.

<% @user.roles.each do |role| %>
    <%= f.hidden_field :role_ids, :multiple => true, :value => role.id %>
<% end %>

:multiple adds both the [] to the end of the name attribute and multiple="multiple" to the input element, which is ideal. Rails uses this internally when it generates inputs for arrays, such as in fields_for.

Unfortunately it is not well-documented. I'm going to look into fixing this.

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6 Comments

This does work in Rails 4 altho it generates inputs with the same id.
Doesn't work for me in Rails 4.0.2 when using form_tag with hidden_field_tag, I would only get the last role in params[:role_ids]. Using hidden_field_tag 'role_ids[]' works fine.
@JeremyF. It won't work with hidden_field_tag, it has to be hidden_field.
If you do want to use hidden_field_tag, then <%= hidden_field_tag('role_ids[]', role.id) %>
Is there now documentation? If yes, could you give me a link? Thanks
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17

The only thing that works for me (Rails 3.1) is using hidden_field_tag:

<% @users.roles.each do |role| %>
    <%= hidden_field_tag "user_role_ids[]", role.id %>
<% end %>
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1 Comment

The double quotes around user_role_ids[] are important. Single quotes didn't work for me.
3

Try: 

 <% @user.roles.each_with_index do |role| %>
    <%= f.hidden_field "role_ids[]", :value => role.id %>
 <% end %>
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3 Comments

that seems to make a hash - perhaps I'll hack around with it.
This is close, What ended up working was...<% f.fields_for :users do |builder| %> <%= render 'user_fields', :f => builder %> <% end %> THEN <% role = Role.find(:first) %> <%= f.hidden_field :role_ids, :value => role.id %>
This is how it worked for me ` <% @user.roles.each do |role| %> <%= f.hidden_field "role_ids][", :value => role.id %> <% end %>` .... Remember to reverse the brackets for role_ids][. If I don't reverse the brackets I get nil in the array for role_ids param in my server logs, with reverse brackets it works like charm. Don't know why it works, it would be great if somebody could explain it.
3

using Rails 4.2.6

I was able to use

<% @user.roles.each do |role|
  <%= f.hidden_field :role_ids, :id => role.id, :value => role.id, :multiple => true %>
<% end %>

which rendered:

<input id="12345" value="12345" multiple="multiple" type="hidden" name="role_form[role_ids][]">

trying to use hidden_field_tag or the 'role_ids[]' the param details were not being included in my form_params.

This didn't work:

<% @user.roles.each do |role|
  <%= hidden_field_tag 'role_ids[]', role %>
<% end %>

because it renders:

<input type="hidden" name="role_ids[]" id="role_ids_" value="12345">

and is seen by the controller outside of the form params.

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2

try with:

<%= f.hidden_field :role_ids, :value => @user.roles.map(&:id).join(", ") %>

edit: note - you'll need to do ids.split(", ") in your controller to convert them from a string into an array

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2 Comments

Close but it still doesn't work. Required Output: "role_ids"=>["2", "4"] Actual Output: "role_ids"=>"2, 4"
Still, I found this to be the best solution, just naming the hidden field something like :concatenated_role_ids instead and adding something like params[:role_ids] ||= params.require(:concatenated_role_ids).split(', ') to the top of the controller action.
1

I realize the original question involved a Rails form_for form, but I just encountered this problem while trying adding a hidden field to a form_tag form. The solution is slightly different.

The hidden_field_tag kept converting my ids to a space-separated string, like "1 2 3", not the array of ["1", "2", "3"] that I wanted. According to the docs, this is a known problem with hidden_field_tag. This is the approach that ended up working for my Rails 6 form_tag form:

In the view:

<%= hidden_field_tag :role_ids, my_role_ids_array %>

In the controller:

role_ids = params[:role_ids].split(' ').map(&:to_i)
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0

Could solve this kind of issue with :

      <% params[:filter].each do |filter| %>
        <%= hidden_field_tag 'filter[]', filter %>
      <% end %>
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