link to submission preview page in completed emails

db/migrate/20231119222105_add_slug_to_submissions.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+class AddSlugToSubmissions < ActiveRecord::Migration[7.0]
+  class MigrationSubmission < ApplicationRecord
+    self.table_name = 'submissions'
+  end
+
+  def up
+    add_column :submissions, :slug, :string
+
+    MigrationSubmission.where(slug: nil).find_each do |submission|
+      submission.update_columns(slug: SecureRandom.base58(14))
+    end
+
+    change_column_null :submissions, :slug, false
+
+    add_index :submissions, :slug, unique: true
+  end
+
+  def down
+    remove_column :submissions, :slug
+  end
+end