add id_seq reset for PostgreSQL databases

lib/create_or_update.rb

@@ -24,4 +24,13 @@ class ActiveRecord::Base
     end
     record
   end
+
+  # for PostgreSQL (and others?) we must reset the id sequential to the next
+  # available highest number. This happens because the create_or_update
+  # creates records with an id already set, bypassing PostgreSQL's automatic
+  # incrementing sequential id counter
+  # Otherwise, we get the dreaded "duplicate key value violates unique constraint" error
+  def self.postgresql_reset_id_seq
+    connection.execute("SELECT setval('#{self.table_name}_id_seq'::regclass, MAX(id)) FROM #{self.table_name}")
+  end
 end