FEATURE: add a way to map arbitrary urls to a topic, post, or category. Useful for sites that have migrated to Discourse and want to redirect from their old site to Discourse with 301 redirects.

app/models/permalink.rb

@@ -0,0 +1,21 @@
+class Permalink < ActiveRecord::Base
+  belongs_to :topic
+  belongs_to :post
+  belongs_to :category
+
+  before_validation :normalize_url
+
+  def normalize_url
+    if self.url
+      self.url = self.url.strip
+      self.url = self.url[1..-1] if url[0,1] == '/'
+    end
+  end
+
+  def target_url
+    return post.url if post
+    return topic.relative_url if topic
+    return category.url if category
+    nil
+  end
+end