#264

backend/db/migrate/20260409123700_create_post_versions.rb

@@ -1,3 +1,6 @@
+require 'set'
+
+
 class CreatePostVersions < ActiveRecord::Migration[8.0]
   class Post < ApplicationRecord
     self.table_name = 'posts'
@@ -27,44 +30,122 @@ class CreatePostVersions < ActiveRecord::Migration[8.0]
       t.references :created_by_user, foreign_key: { to_table: :users }
 
       t.index [:post_id, :version_no], unique: true
-      t.check_constraint 'version_no > 0'
-      t.check_constraint "event_type IN ('create', 'update', 'discard', 'restore')"
+      t.check_constraint 'version_no > 0',
+                         name: 'post_versions_version_no_positive'
+      t.check_constraint "event_type IN ('create', 'update', 'discard', 'restore')",
+                         name: 'post_versions_event_type_valid'
     end
 
+    PostVersion.reset_column_information
+
     say_with_time 'Backfilling post_versions' do
       Post.find_in_batches(batch_size: 500) do |posts|
         post_ids = posts.map(&:id)
 
-        tag_names_by_post_id =
+        post_tag_rows_by_post_id =
             PostTag
             .joins('INNER JOIN tags ON tags.id = post_tags.tag_id')
             .joins('INNER JOIN tag_names ON tag_names.id = tags.tag_name_id')
             .where(post_id: post_ids)
-            .where('post_tags.discarded_at IS NULL')
-            .where('tags.discarded_at IS NULL')
-            .where('tag_names.discarded_at IS NULL')
-            .pluck('post_tags.post_id', 'tag_names.name')
-            .each_with_object(Hash.new { |h, k| h[k] = [] }) do |(post_id, tag_name), h|
-              h[post_id] << tag_name
+            .pluck('post_tags.post_id',
+                   'post_tags.created_at',
+                   'post_tags.discarded_at',
+                   'post_tags.created_user_id',
+                   'post_tags.deleted_user_id',
+                   'tag_names.name')
+            .each_with_object(Hash.new { |h, k| h[k] = [] }) do |row, h|
+              post_id, created_at, discarded_at, created_user_id, deleted_user_id, tag_name = row
+              h[post_id] << { created_at:,
+                              discarded_at:,
+                              created_user_id:,
+                              deleted_user_id:,
+                              tag_name: }
             end
 
-        rows = posts.map do |post|
-          tags = tag_names_by_post_id[post.id].uniq.sort.join(' ')
-          { post_id: post.id,
-            version_no: 1,
+        rows = []
+
+        posts.each do |post|
+          post_tag_rows = post_tag_rows_by_post_id[post.id]
+
+          events = post_tag_rows.flat_map do |post_tag_row|
+            ary = [[post_tag_row[:created_at],
+                    post_tag_row[:created_user_id],
+                    :add,
+                    post_tag_row[:tag_name]]]
+
+            if post_tag_row[:discarded_at]
+              ary << [post_tag_row[:discarded_at],
+                      post_tag_row[:deleted_user_id],
+                      :remove,
+                      post_tag_row[:tag_name]]
+            end
+
+            ary
+          end
+
+          kind_order = { add: 0, remove: 1 }
+
+          events.sort_by! do |event_at, user_id, kind, tag_name|
+            [event_at, user_id || 0, kind_order.fetch(kind), tag_name]
+          end
+
+          event_buckets = bucket_events(events)
+
+          active_tags = Set.new
+          version_no = 0
+
+          if event_buckets.empty?
+            version_no += 1
+            rows << build_row(post:,
+                              version_no:,
                               event_type: 'create',
-            title: post.title,
-            url: post.url,
-            thumbnail_base: post.thumbnail_base,
-            tags:,
-            parent_id: post.parent_id,
-            original_created_from: post.original_created_from,
-            original_created_before: post.original_created_before,
                               created_at: post.created_at,
-            created_by_user_id: post.uploaded_user_id }
+                              created_by_user_id: post.uploaded_user_id,
+                              tags: [])
+            next
           end
 
-        PostVersion.insert_all!(rows) if rows.present?
+          first_bucket = event_buckets.first
+          merge_first_bucket_into_create = first_bucket[:first_at] <= post.created_at + 1.second
+
+          if merge_first_bucket_into_create
+            event_buckets.shift
+            apply_bucket!(active_tags, first_bucket)
+
+            version_no += 1
+            rows << build_row(
+                post:,
+                version_no:,
+                event_type: 'create',
+                created_at: post.created_at,
+                created_by_user_id: post.uploaded_user_id || first_bucket[:user_ids].compact.first,
+                tags: active_tags.to_a.sort)
+          else
+            version_no += 1
+            rows << build_row(
+                post:,
+                version_no:,
+                event_type: 'create',
+                created_at: post.created_at,
+                created_by_user_id: post.uploaded_user_id,
+                tags: [])
+          end
+
+          event_buckets.each do |bucket|
+            apply_bucket!(active_tags, bucket)
+
+            version_no += 1
+            rows << build_row(
+                post:,
+                version_no:,
+                event_type: 'update',
+                created_at: bucket[:first_at],
+                created_by_user_id: bucket[:user_ids].compact.first,
+                tags: active_tags.to_a.sort)
+          end
+        end
+
+        PostVersion.insert_all!(rows) if rows.any?
       end
     end
   end
@@ -72,4 +153,51 @@ class CreatePostVersions < ActiveRecord::Migration[8.0]
   def down
     drop_table :post_versions
   end
+
+  private
+
+  def bucket_events events
+    buckets = []
+
+    events.each do |event_at, user_id, kind, tag_name|
+      if buckets.empty? || event_at - buckets.last[:last_at] > 1.second
+        buckets << { first_at: event_at,
+                     last_at: event_at,
+                     user_ids: [user_id],
+                     events: [[kind, tag_name]] }
+      else
+        bucket = buckets.last
+        bucket[:last_at] = event_at
+        bucket[:user_ids] << user_id
+        bucket[:events] << [kind, tag_name]
+      end
+    end
+
+    buckets
+  end
+
+  def apply_bucket! active_tags, bucket
+    bucket[:events].each do |kind, tag_name|
+      if kind == :add
+        active_tags.add(tag_name)
+      else
+        active_tags.delete(tag_name)
+      end
+    end
+  end
+
+  def build_row post:, version_no:, event_type:, created_at:, created_by_user_id:, tags:
+    { post_id: post.id,
+      version_no:,
+      event_type:,
+      title: post.title,
+      url: post.url,
+      thumbnail_base: post.thumbnail_base,
+      tags: tags.join(' '),
+      parent_id: post.parent_id,
+      original_created_from: post.original_created_from,
+      original_created_before: post.original_created_before,
+      created_at:,
+      created_by_user_id: }
+  end
 end

backend/db/schema.rb

@@ -149,8 +149,8 @@ ActiveRecord::Schema[8.0].define(version: 2026_04_09_123700) do
     t.index ["parent_id"], name: "index_post_versions_on_parent_id"
     t.index ["post_id", "version_no"], name: "index_post_versions_on_post_id_and_version_no", unique: true
     t.index ["post_id"], name: "index_post_versions_on_post_id"
-    t.check_constraint "`event_type` in (_utf8mb4'create',_utf8mb4'update',_utf8mb4'discard',_utf8mb4'restore')"
-    t.check_constraint "`version_no` > 0"
+    t.check_constraint "`event_type` in (_utf8mb4'create',_utf8mb4'update',_utf8mb4'discard',_utf8mb4'restore')", name: "post_versions_event_type_valid"
+    t.check_constraint "`version_no` > 0", name: "post_versions_version_no_positive"
   end
 
   create_table "posts", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|