title: Seeds.rb sets primary key value, results in duplicate key error
body: <p>In my Rails 4 app, which I am using on Heroku for production, I have set up a seeds.rb file for the initial set of data. As it is critical that a few records have specific primary ids, say in the 'activities' table, I have set those. All goes well.</p>
  
  <p>UNTIL. Until I need to add a new activity to the activities table. Adding a new record will fail as many times as there are records in that table, while the sequencer catches up. (e.g. if I have three records, new record creation fails three times, succeeds on the fourth).</p>
  
  <p>QUESTION: How can I get the primary ID counter on the Heroku postgres database to start after the highest primary id set in my seeds.rb file? If you don't know, what terms should I be googling?</p>
  
  <p>Ideally, this solution would be automatic, and not something I have to open psql for each time I seed the database.</p>
  
  <p>Thanks in advance.</p>