Model concerns organization into module namespaces (#28149)

app/models/concerns/account/merging.rb

@@ -0,0 +1,56 @@
+# frozen_string_literal: true
+
+module Account::Merging
+  extend ActiveSupport::Concern
+
+  def merge_with!(other_account)
+    # Since it's the same remote resource, the remote resource likely
+    # already believes we are following/blocking, so it's safe to
+    # re-attribute the relationships too. However, during the presence
+    # of the index bug users could have *also* followed the reference
+    # account already, therefore mass update will not work and we need
+    # to check for (and skip past) uniqueness errors
+
+    owned_classes = [
+      Status, StatusPin, MediaAttachment, Poll, Report, Tombstone, Favourite,
+      Follow, FollowRequest, Block, Mute,
+      AccountModerationNote, AccountPin, AccountStat, ListAccount,
+      PollVote, Mention, AccountDeletionRequest, AccountNote, FollowRecommendationSuppression,
+      Appeal
+    ]
+
+    owned_classes.each do |klass|
+      klass.where(account_id: other_account.id).reorder(nil).find_each do |record|
+        record.update_attribute(:account_id, id)
+      rescue ActiveRecord::RecordNotUnique
+        next
+      end
+    end
+
+    target_classes = [
+      Follow, FollowRequest, Block, Mute, AccountModerationNote, AccountPin,
+      AccountNote
+    ]
+
+    target_classes.each do |klass|
+      klass.where(target_account_id: other_account.id).reorder(nil).find_each do |record|
+        record.update_attribute(:target_account_id, id)
+      rescue ActiveRecord::RecordNotUnique
+        next
+      end
+    end
+
+    CanonicalEmailBlock.where(reference_account_id: other_account.id).find_each do |record|
+      record.update_attribute(:reference_account_id, id)
+    end
+
+    Appeal.where(account_warning_id: other_account.id).find_each do |record|
+      record.update_attribute(:account_warning_id, id)
+    end
+
+    # Some follow relationships have moved, so the cache is stale
+    Rails.cache.delete_matched("followers_hash:#{id}:*")
+    Rails.cache.delete_matched("relationships:#{id}:*")
+    Rails.cache.delete_matched("relationships:*:#{id}")
+  end
+end