Improve not_occupied solution
Not being a subquery is better! I realized later that a LEFT JOIN would probably do it even betterer? with like `HAVING count(x) = 0`? but the `left_outer_joins` method doesn't seem to be in Rails 4, and I don't want to do stringy joins, so this is fine for now!
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@ -87,11 +87,15 @@ class Item < ActiveRecord::Base
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zone_ids = Zone.matching_label(zone_label, locale).map(&:id)
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i = Item.arel_table
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sa = SwfAsset.arel_table
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psa = ParentSwfAssetRelationship.arel_table
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subquery = SwfAsset.select('COUNT(*)').joins(:parent_swf_asset_relationships).
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where(psa[:parent_type].eq('Item')).where(psa[:parent_id].eq(i[:id])).
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where(sa[:zone_id].in(zone_ids))
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where("(#{subquery.to_sql}) = 0")
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# Querying for "has NO swf_assets matching these zone IDs" is trickier than
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# the positive case! To do it, we GROUP_CONCAT the zone_ids together for
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# each item, then use FIND_IN_SET to search the result for each zone ID,
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# and assert that it must not find a match. (This is uhh, not exactly fast,
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# so it helps to have other tighter conditions applied first!)
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# TODO: I feel like this could also be solved with a LEFT JOIN, idk if that
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# performs any better? In Rails 5+ `left_outer_joins` is built in so!
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condition = zone_ids.map { 'FIND_IN_SET(?, GROUP_CONCAT(zone_id)) = 0' }.join(' AND ')
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joins(:swf_assets).group(i[:id]).having(condition, *zone_ids).distinct
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}
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scope :restricts, ->(zone_label, locale = I18n.locale) {
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zone_ids = Zone.matching_label(zone_label, locale).map(&:id)
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