Rails: How do I use hidden_field in a form_for?

Ref hidden_field or hidden_field_tag

<% form_for(:request, :url => requests_path) do |f| %>    <div class="actions">        <%= f.hidden_field :some_column %>        <%= hidden_field_tag 'selected', 'none'  %>        <%= f.submit e %>    </div><% end %>

then in controller

 params[:selected]="none" params[:request][:some_column] = request.some_column

Note when you used

   <%= f.hidden_field :some_column %>

it change to html

<input type="hidden" id="request_some_column" name="request[some_column]" value="#{@request.some_column}" />

and when you used

<%= hidden_field_tag 'selected', 'none'  %>

it change to html

   <input id="selected" name="selected" type="hidden" value="none"/>

You can send a custom value as a hidden input for your model like that:

<%= f.hidden_field :your_model_field_name, value: 12 %>

Where value: 12 is just a demo, but you can pass whatever value you need.

To elaborate more on Bruno Paulino's answer.

I had this same concern when working on a Rails 6 application.

I had a form for books, but I needed to pass in the current user's id into the form for each book that will be created in a hidden manner.

My initial form field was this way:

<div class="field">  <%= form.label :user_id %>  <%= form.text_field :user_id %></div>

I had to modify it to this using this:

<div class="field">  <%= form.hidden_field :model_field_name, value: field_value %></div>

So I had this after on:

<div class="field">  <%= form.hidden_field :user_id, value: current_user.id %></div>

That's all.

I hope this helps