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