rails 3 group by and sum

Question

I have the following model:

activity_types: id, name

activities: id, id_activity_type, occurrences, date (other fields)

The activities tab

Answer 1

Activity.joins(:activity_types).group('activity_types.name').sum(:occurrences)

SELECT SUM(activities.occurrences) AS sum_occurrences, activity_types.name AS activity_types_name FROM activity_types INNER JOIN activity_types ON activity_types.id = activities.activity_types_id GROUP BY activity_types.name

in case you needed an ordered hash based on activity_types.id and assuming activity_types_id is not needed as a part of hash key.

Activity.joins(:activity_types).group('activity_types.name').order(:activity_types_id).sum(:occurrences)

incase [activity_type_id, activity_types.name] needed as a part of key

Activity.joins(:activity_types).group(:activity_types_id, 'activity_types.name').order(:activity_types_id).sum(:occurrences)