#442

backend/app/controllers/post_versions_controller.rb

@@ -15,7 +15,6 @@ class PostVersionsController < ApplicationController
     offset = (page - 1) * limit
 
     q = HistoryAccess.visible(PostVersion.all)
-    q = q.with_previous_version if tag_id || external_tag_id
     q = q.where('post_versions.post_id = ?', post_id) if post_id
     q = q.with_previous_version if tag_id || external_tag_id
     if external_tag_id || (tag_id && !(Tag.exists?(id: tag_id)))
@@ -34,7 +33,7 @@ class PostVersionsController < ApplicationController
                 .limit(limit)
                 .offset(offset)
                 .pluck('post_versions.id')
-    versions = HistoryAccess.visible(version_scope.where(id: ids))
+    versions = version_scope.merge(q).where(id: ids)
         .order(Arel.sql('post_versions.created_at DESC, post_versions.id DESC'))
 
     render json: { versions: serialise_versions(versions, locale.language_code), count:, population_count: HistoryAccess.population_count(PostVersion) }

backend/app/controllers/posts_controller.rb

@@ -37,7 +37,7 @@ class PostsController < ApplicationController
 
     offset = (page - 1) * limit
 
-    updated_at_all_sql = 'posts.updated_at'
+    needs_history_join = order[0] == 'updated_at' || updated_between.any?(&:present?)
 
     q =
         filtered_posts(locale)
@@ -56,12 +56,25 @@ class PostsController < ApplicationController
     end
     q = q.where('posts.created_at >= ?', created_between[0]) if created_between[0]
     q = q.where('posts.created_at <= ?', created_between[1]) if created_between[1]
+    count_scope = q
+    if needs_history_join
+      history_times = HistoryAccess.visible(PostVersion.all)
+          .select('post_id, MAX(created_at) AS latest_at').group(:post_id)
+      q = q.joins("LEFT JOIN (#{ history_times.to_sql }) history_times " +
+                  'ON history_times.post_id = posts.id')
+      updated_at_all_sql = 'GREATEST(posts.updated_at, ' +
+          'COALESCE(history_times.latest_at, posts.updated_at))'
+    end
     if updated_between[0]
       q = q.where("#{ updated_at_all_sql } >= ?", updated_between[0])
     end
     if updated_between[1]
       q = q.where("#{ updated_at_all_sql } <= ?", updated_between[1])
     end
+    count_scope = q if updated_between.any?(&:present?)
+    if needs_history_join
+      q = q.select('posts.*', "#{ updated_at_all_sql } AS updated_at")
+    end
 
     sort_sql =
         case order[0]
@@ -78,14 +91,20 @@ class PostsController < ApplicationController
              .limit(limit)
              .offset(offset)
              .to_a
-    latest_version_times = HistoryAccess.visible(PostVersion.where(post_id: posts.map(&:id)))
-        .group(:post_id).maximum(:created_at)
+    latest_version_times =
+        if needs_history_join
+          { }
+        else
+          HistoryAccess.visible(PostVersion.where(post_id: posts.map(&:id)))
+              .group(:post_id).maximum(:created_at)
+        end
 
-    q = q.except(:select, :order)
+    count_scope = count_scope.except(:select, :order)
 
     render json: { posts: posts.map { |post|
+      updated_at = [post.updated_at, latest_version_times[post.id]].compact.max
       PostRepr.base(post, language_code: locale.language_code)
-              .merge(updated_at: post.updated_at).tap do |json|
+          .merge('updated_at' => updated_at).tap do |json|
         json['thumbnail'] =
             if post.thumbnail.attached?
               rails_storage_proxy_url(post.thumbnail, only_path: false)
@@ -93,7 +112,7 @@ class PostsController < ApplicationController
               nil
             end
       end
-    }, count: q.group_values.present? ? q.count.size : q.count }
+    }, count: count_scope.group_values.present? ? count_scope.count.size : count_scope.count }
   end
 
   def random

backend/app/models/history_access.rb

@@ -59,20 +59,21 @@ class HistoryAccess < ActiveSupport::CurrentAttributes
   end
 
   def self.json_reference(table, key, document)
-    "NOT EXISTS (SELECT 1 FROM JSON_TABLE(COALESCE(#{ document }, JSON_ARRAY()), " +
+    # A scalar lookup avoids MySQL's semijoin rewrite losing the JSON row correlation.
+    "(SELECT 1 FROM JSON_TABLE(COALESCE(#{ document }, JSON_ARRAY()), " +
         "'$[*]' COLUMNS (reference_id BIGINT PATH '$' NULL ON EMPTY)) reference_entry " +
         "JOIN (#{ discarded_keys(table, key) }) blocked " +
-        "ON reference_entry.reference_id = blocked.#{ key })"
+        "ON reference_entry.reference_id = blocked.#{ key } LIMIT 1) IS NULL"
   end
 
   def self.list_reference(table, key, document)
     # Preserve FIND_IN_SET's exact token semantics, including empty tokens.
     array = "CONCAT('[', REPLACE(JSON_QUOTE(REPLACE(COALESCE(#{ document }, ''), " +
         "' ', ',')), ',', '\",\"'), ']')"
-    "NOT EXISTS (SELECT 1 FROM JSON_TABLE(#{ array }, '$[*]' " +
+    "(SELECT 1 FROM JSON_TABLE(#{ array }, '$[*]' " +
         "COLUMNS (reference_id VARCHAR(255) PATH '$')) reference_entry " +
         "JOIN (#{ discarded_keys(table, key) }) blocked " +
-        "ON reference_entry.reference_id = CAST(blocked.#{ key } AS CHAR))"
+        "ON reference_entry.reference_id = CAST(blocked.#{ key } AS CHAR) LIMIT 1) IS NULL"
   end
 
   def self.snapshot_reference(model, row, external: false)
@@ -91,8 +92,8 @@ class HistoryAccess < ActiveSupport::CurrentAttributes
       match += ' AND reference_version.version_no = tag_reference.version_no'
       latest = ''
     end
-    "NOT EXISTS (SELECT 1 FROM #{ source } JOIN #{ table } reference_version ON #{ match } " +
-        "WHERE NOT (#{ sql(model, 'reference_version') }) #{ latest })"
+    "(SELECT 1 FROM #{ source } JOIN #{ table } reference_version ON #{ match } " +
+        "WHERE NOT (#{ sql(model, 'reference_version') }) #{ latest } LIMIT 1) IS NULL"
   end
 
   def self.reference_sql(table, row)