Merge pull request #8736 from gschlager/rename_reply_id_column

REFACTOR: Rename `post_replies.reply_id` column to `post_replies.reply_post_id`

db/migrate/20200116140132_rename_reply_id_column.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+class RenameReplyIdColumn < ActiveRecord::Migration[6.0]
+  def up
+    Migration::ColumnDropper.mark_readonly(:post_replies, :reply_id)
+
+    add_column :post_replies, :reply_post_id, :integer
+
+    execute <<~SQL
+      UPDATE post_replies
+      SET reply_post_id = reply_id
+    SQL
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end

db/migrate/20200117141138_update_post_reply_indexes.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+class UpdatePostReplyIndexes < ActiveRecord::Migration[6.0]
+  # Adding and removing indexes concurrently doesn't work within transaction.
+  # It also needs existence checks for indexes in case the migration fails and needs to run again.
+  disable_ddl_transaction!
+
+  def up
+    if !index_exists?(:post_replies, [:post_id, :reply_post_id])
+      add_index :post_replies, [:post_id, :reply_post_id], unique: true, algorithm: :concurrently
+    end
+
+    if !index_exists?(:post_replies, [:reply_post_id])
+      add_index :post_replies, [:reply_post_id], algorithm: :concurrently
+    end
+
+    if index_exists?(:post_replies, [:post_id, :reply_id])
+      remove_index :post_replies, column: [:post_id, :reply_id], algorithm: :concurrently
+    end
+
+    if index_exists?(:post_replies, [:reply_id])
+      remove_index :post_replies, column: [:reply_id], algorithm: :concurrently
+    end
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end