How to show a points leaderboard

You will need to override Merit::Score model adding a top_scored method.

NOTE: if you use merit version >= 4, the superclass name has changed to work with zeitwerk. See https://github.com/merit-gem/merit/issues/343.

For doing so, you can create config/initializers/merit_scores_override.rb with following contents:

module Merit
  class Score
    # Meant to display a leaderboard. Accepts options :table_name (users by
    # default), :since_date (1.month.ago by default) and :limit (10 by
    # default).
    #
    # It lists top 10 scored objects in the last month by default.
    #
    # This is a postgresql snippet, you may need to tweak it for other ORMs.
    def self.top_scored(options = {})
      options[:table_name] ||= :users
      options[:since_date] ||= 1.month.ago
      options[:limit]      ||= 10

      alias_id_column = "#{options[:table_name].to_s.singularize}_id"
      if options[:table_name] == :sashes
        sash_id_column = "#{options[:table_name]}.id"
      else
        sash_id_column = "#{options[:table_name]}.sash_id"
      end

      # MeritableModel - Sash -< Scores -< ScorePoints
      sql_query = <<SQL
SELECT
  #{options[:table_name]}.id AS #{alias_id_column},
  SUM(num_points) as sum_points
FROM #{options[:table_name]}
  LEFT JOIN merit_scores ON merit_scores.sash_id = #{sash_id_column}
  LEFT JOIN merit_score_points ON merit_score_points.score_id = merit_scores.id
WHERE merit_score_points.created_at > '#{options[:since_date]}'
GROUP BY #{options[:table_name]}.id, merit_scores.sash_id
ORDER BY sum_points DESC
LIMIT #{options[:limit]}
SQL
      results = ActiveRecord::Base.connection.execute(sql_query)
      results.map do |h|
        h.keep_if { |k, v| (k == alias_id_column) || (k == 'sum_points') }
      end
      results
    end
  end
end

You could use it like:

# List top 10 scored users in the last month
Merit::Score.top_scored
# =>  [{"user_id"=>2, "sum_points"=>5}, {"user_id"=>1, "sum_points"=>1}]

# List top 25 scored lists in the last week
Merit::Score.top_scored(
  # table_name: :lists, # if a List was granted points instead of a User
  since_date: 1.week.ago,
  limit: 25
)
# =>  [{"user_id"=>2, "sum_points"=>5}, {"user_id"=>1, "sum_points"=>1}, ...]

See also https://github.com/merit-gem/merit/issues/242 for custom SQL to build leaderboards grouped by companies.