Question

If I check multiple records in my view then hit the delete button,
discard action will be called.

Now I only can delete(untrash) 1 record at once.
Why can’t I delete all of them at once even if I check multiple records???

view

  <%= form_tag(:action => discard, :via => 'put') do %>   
   <% @messages.each do |m| %>
      <tr>
       <td><%= check_box_tag "id",m.id %></td>
       <td><%= m.last_message.id %></td>
       <td><%= 'unread' if m.is_unread?(current_user) %></td>
       <td><%= m.last_message.created_at.to_s(:jp) %></td>
       <td><%= m.last_sender.username %></td>
       <td><%= link_to m.subject, show_messages_path(m) %></td>
      </tr>
   <% end %>
   <%= submit_tag "delete", :class => 'btn' %>
  <% end %>

controller

  def discard

      conversation = Conversation.find_all_by_id(params[:id])
    if conversation
      current_user.trash(conversation)
      flash[:notice] = "Message sent to trash."
    else
      conversations = Conversation.find(params[:conversations])
      conversations.each { |c| current_user.trash(c) }
      flash[:notice] = "Messages sent to trash."
    end
       redirect_to :back 
  end

routes

match 'messages/discard(/:id)' => 'messages#discard' , :as => :discard_messages

Answer 1

When there are multiple inputs of the same name the last one ‘wins’ – params[:id] will be the value of the last submitted input, so only one message is deleted (this is easily visible by inspecting the value of the params hash)

If the input name ends with [] (i.e. in your case set the name to id[] then rails will instead collect all the values into an array.