How to remember active_storage file name when validation fails in controller

Question

In a rails 5.2.3 app, I have a model Post, which uses active_storage to attach a file and has fields for duration and place. The duration must be present.

class Post
  has_one_attached :video
  validates :duration, presence: true
end

Using simple_form the fields in the form are declared as

<%= f.input :duration %>
<%= f.input :place %>
<%= f.input :video %>

The controller has the following logic for the create

def create
    @post = current_user.posts.build(post_params)
    if @post.save
      flash[:success] = 'Post has been saved'
      redirect_to root_path
    else
      @title = 'New Post'
      @user = current_user
      render :new
    end
  end

  private

  def post_params
    params.require(:post).permit(:duration, :video)
  end

If the validation fails, the form shows value of place, but I lose the file name for the video. This means the user has to choose the file again. How do I fix this?

Answer 1

Following Thanh's suggestion, I did check this SO question, and tried changing the simple_form field to

<%= f.hidden_field :video, value: f.object.image.signed_id if f.object.video.attached? %>
<%= f.file_field :video %>

This remembered the file name, but did not display it. So I did the following work around:

<% if f.object.video.attached? %>
  <span><strong>Video File Name:</strong> <%= f.object.video.blob.filename.to_s  %>. To change, choose different file below:</span>
<% end %>
    <%= f.hidden_field :video, value: f.object.image.signed_id if f.object.video.attached? %>
<%= f.file_field :video %>