Rails 4: replace / delete uploaded file in edit view form - ruby-on-rails

Question

A similar question has already been asked, but the answer is only for Rails 3, so I am taking the liberty of asking a new question.
I have a Rails 4 app, with the following models:
class User < ActiveRecord::Base
has_many :administrations
has_many :calendars, through: :administrations
end
class Calendar < ActiveRecord::Base
has_many :administrations
has_many :users, through: :administrations
has_many: :posts
end
class Administration < ActiveRecord::Base
belongs_to :user
belongs_to :calendar
end
class Post < ActiveRecord::Base
belongs_to :calendar
end
The Post model has the following attributes:
references :calendar, index: true, foreign_key: true
date :date
time :time
string :subject
string :format
text :copy
attachment :image
and the attachment was setup as follows with Paperclip in Post model:
has_attached_file :image, styles: { small: "64x64", med: "100x100", large: "200x200" }
validates_attachment :image, :content_type => { :content_type => "image/png" },
:size => { :in => 0..3000.kilobytes }
Adding an image to a Post is working fine, through the following form:
<%= form_for [#calendar, #calendar.posts.build] do |f| %>
<% if #post.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(#post.errors.count, "error") %> prohibited this post from being saved:</h2>
<ul>
<% #post.errors.full_messages.each do |message| %>
<li><%= message %></li>
<% end %>
</ul>
</div>
<% end %>
<div class="field">
<p>
<%= f.label :date %><br>
<%= f.date_select :date %>
</p>
<p>
<%= f.label :time %><br>
<%= f.time_select :time %>
</p>
<p>
<%= f.label :subject %><br>
<%= f.text_field :subject %>
</p>
<p>
<%= f.label :format %><br>
<%= f.text_field :format %>
</p>
<p>
<%= f.label :copy %><br>
<%= f.text_area :copy %>
</p>
<p>
<%= f.label :image %><br>
<%= f.file_field :image %>
</p>
</div>
<div class="actions">
<%= f.submit %>
</div>
<% end %>
Viewing the image attached to a Post is also working well, thanks to this show view:
<h2>Post from <%= #post.date.strftime("%A, %d") %></h2>
<div>
<p><strong>Date</strong></p>
<%= #post.date.strftime("%A, %d") %>
</div>
<div>
<p><strong>Time</strong></p>
<%= #post.time.strftime("%I:%M %p") %>
</div>
<div>
<p><strong>Subject</strong></p>
<%= #post.subject %>
</div>
<div>
<p><strong>Format</strong></p>
<%= #post.format %>
</div>
<div>
<p><strong>Copy</strong></p>
<%= #post.copy %>
</div>
<div>
<p><strong>Image</strong></p>
<%= image_tag #post.image.url(:med) %>
</div>
However, when I go to the edit view, for a post where I have previously uploaded an image, I only see the field that allows me to add an image and a message saying "no file chosen".
The edit view uses (for now) the same form as the new view, as shown above.
How can I achieve the following:
Have the uploaded image appear in the edit page.
Allow users to delete this image.
Allow users to replace this image with a new one.
–––––
UPDATE: I found a way to solve item #1 above, by replacing
<p>
<%= f.label :image %><br>
<%= f.file_field :image %>
</p>
with
<p>
<%= f.label :image %><br>
<% if #post.image.exists? %>
<%= image_tag #post.image.url(:med) %>
<% else %>
<%= f.file_field :image %>
<% end %>
</p>
in my Post edit view.
I am still working on items #2 & #3 and could definitely use some help with these.
–––––
I am happy to share more code if necessary.
Any idea?

Answer 1

For #2 - Allow user to delete image, you might find this SO Issue helpful
OR, as per Paperclip's documentation you could simply create a dummy checkbox and, in the update method of your controller, look if the checkbox has been ticked and delete the attachment as mentioned in the documentation.
For #3 - Allow users to replace this image with a new one
Simply rework your code as follow:
<p>
<%= f.label :image %><br>
<% if #post.image.exists? %>
<%= image_tag #post.image.url(:med) %>
<% end %>
<%= f.file_field :image %>
</p>
This way, the file_field is always present (allowing user to replace or add their image)