Indicate that an uploaded file is present in edit form -- paperclip - ruby-on-rails-4

Question

In my current solution, I am able to put a checkbox in the edit form so that users can delete attachment. However, there is no indication for the user that a file has been uploaded, the name of that file, etc. so that he can decide whether to delete.
Right now the form look like this. The first material is an existing one, the next 3 are due to
def edit
#post = Post.find(params[:id])
3.times { #post.post_materials.new }
end
As you can see, it's very hard to distinguish between them. Ideally, I want the first material file name to appear somehow.
<%= form_for #post, :html => { :multipart => true } do |f| %>
<%= f.label :title %>
<%= f.text_field :title %>
Materials:
<ul>
<%= f.fields_for :materials, :html => { :multipart => true } do |materials_form| %>
<li>
<%= materials_form.label :asset %>
<%= materials_form.file_field :asset %>
<%= materials_form.label :_destroy, class: "checkbox inline" do %>
Remove attachment <%= materials_form.check_box :_destroy %>
<% end %>
</li>
<% end %>
</ul>
<%= f.submit "Submit", class: "btn btn-large" %>
<% end %>

Answer 1

Running paperclip's generator creates a migration to add 4 attributes on your model, as you can see here. These attributes are:
<attachment>_file_name
<attachment>_file_size
<attachment>_content_type
<attachment>_updated_at
So, If you ran the generator this way: rails generate paperclip post_material asset, on your PostMaterial model, you will have these attributes:
asset_file_name
asset_file_size
asset_content_type
asset_updated_at
Then, on your code you can do something like this:
if materials_form.object.asset.exists? #object represents the current post_material instance
#show a label with object.asset_file_name
else
#render materials_form.file_field :asset
end