diff options
Diffstat (limited to 'app/models/event_collection.rb')
-rw-r--r-- | app/models/event_collection.rb | 98 |
1 files changed, 98 insertions, 0 deletions
diff --git a/app/models/event_collection.rb b/app/models/event_collection.rb new file mode 100644 index 00000000000..8b8244314af --- /dev/null +++ b/app/models/event_collection.rb @@ -0,0 +1,98 @@ +# A collection of events to display in an event list. +# +# An EventCollection is meant to be used for displaying events to a user (e.g. +# in a controller), it's not suitable for building queries that are used for +# building other queries. +class EventCollection + # To prevent users from putting too much pressure on the database by cycling + # through thousands of events we put a limit on the number of pages. + MAX_PAGE = 10 + + # projects - An ActiveRecord::Relation object that returns the projects for + # which to retrieve events. + # filter - An EventFilter instance to use for filtering events. + def initialize(projects, limit: 20, offset: 0, filter: nil) + @projects = projects + @limit = limit + @offset = offset + @filter = filter + end + + # Returns an Array containing the events. + def to_a + return [] if current_page > MAX_PAGE + + relation = if Gitlab::Database.join_lateral_supported? + relation_with_join_lateral + else + relation_without_join_lateral + end + + relation.with_associations.to_a + end + + private + + # Returns the events relation to use when JOIN LATERAL is not supported. + # + # This relation simply gets all the events for all authorized projects, then + # limits that set. + def relation_without_join_lateral + events = filtered_events.in_projects(projects) + + paginate_events(events) + end + + # Returns the events relation to use when JOIN LATERAL is supported. + # + # This relation is built using JOIN LATERAL, producing faster queries than a + # regular LIMIT + OFFSET approach. + def relation_with_join_lateral + projects_for_lateral = projects.select(:id).to_sql + + lateral = filtered_events + .limit(limit_for_join_lateral) + .where('events.project_id = projects_for_lateral.id') + .to_sql + + # The outer query does not need to re-apply the filters since the JOIN + # LATERAL body already takes care of this. + outer = base_relation + .from("(#{projects_for_lateral}) projects_for_lateral") + .joins("JOIN LATERAL (#{lateral}) AS #{Event.table_name} ON true") + + paginate_events(outer) + end + + def filtered_events + @filter ? @filter.apply_filter(base_relation) : base_relation + end + + def paginate_events(events) + events.limit(@limit).offset(@offset) + end + + def base_relation + # We want to have absolute control over the event queries being built, thus + # we're explicitly opting out of any default scopes that may be set. + Event.unscoped.recent + end + + def limit_for_join_lateral + # Applying the OFFSET on the inside of a JOIN LATERAL leads to incorrect + # results. To work around this we need to increase the inner limit for every + # page. + # + # This means that on page 1 we use LIMIT 20, and an outer OFFSET of 0. On + # page 2 we use LIMIT 40 and an outer OFFSET of 20. + @limit + @offset + end + + def current_page + (@offset / @limit) + 1 + end + + def projects + @projects.except(:order) + end +end |