code: function findById(id, cb) {
    db.getClient(function(err, client, done) {
      client.query(SELECT_ID, [id], function(err, r) {
        var result = r && r.rows[0];
        if(!err && !result) err = new exceptions.NotFound();
        if(err) {
          cb(err);
          done(err);
        } else {
          cb(null, result);
          done();
        }
      });
    });
  }
docs: Finds a tag by `id`
  
  `cb` is passed the matching tag or exceptions.NotFound
  
  @param {Number} id
  @param {Function} cb