school-platform/app/views/data_files/_form.html.erb

<%= bootstrap_form_for(DataFile.new) do |f| %>
  <%= f.file_field :data, hide_label: true %>
  <%= f.hidden_field :repository_id, value: repository.id %>
  <%= f.hidden_field :repository_type, value: repository.class.name %>
  <%= f.submit 'Upload file', class: 'btn btn-primary' %>
<% end %>