Use the writing role for increment_usage_count (#170)

* use the writing role for increment_usage_count

* Make this backwards compatible with Rails < 6

* Broadcast when Shortener::ShortenedUrl is loaded

* Documented 'Configuring Reader and Writer Multi-DB Roles'

README.rdoc

@@ -260,14 +260,28 @@ If you want more things to happen when a user accesses one of your short urls, y
 
 You can store a `shortened_urls` table in another database and connecting to it by creating a initializer with the following:
 
-```ruby
-ActiveSupport.on_load(:shortener_record) do
-  connects_to(database: { writing: :dbname, reading: :dbname_replica })
-end
-```
+    ActiveSupport.on_load(:shortener_record) do
+      connects_to(database: { writing: :dbname, reading: :dbname_replica })
+    end
 
 **Note:** Please, replace `dbname` and `dbname_replica` to match your database configuration.
 
+=== Configuring Reader and Writer Multi-DB Roles
+
+Shortener has one write operation that happens on a GET request. To allow this you can override this method in an initializer.
+
+    module ShortenerWriterMonkeyPatch
+      def increment_usage_count
+        ActiveRecord::Base.connected_to(role: :writing) do
+          self.class.increment_counter(:use_count, id)
+        end
+      end
+    end
+
+    ActiveSupport.on_load(:shortener_shortened_url) do
+      Shortener::ShortenedUrl.prepend(ShortenerWriterMonkeyPatch)
+    end
+
 == Contributing
 
 We welcome new contributors. Because we're all busy people, and because Shortener

app/models/shortener/shortened_url.rb

@@ -147,3 +147,5 @@ def generate_unique_key(retries = Shortener.persist_retries)
     end
   end
 end
+
+ActiveSupport.run_load_hooks :shortener_shortened_url, Shortener::ShortenedUrl