When migrating threads and posts together with users the threads and the posts will be assigned as created by the user with the uid from myBB which is not the same in flarum if a user was ever deleted in myBB. This can (and in my case) let the migration fail with the following error due to the user not existing in flarum:
Next Illuminate\Database\QueryException: SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails (`forum`.`posts`, CONSTRAINT `posts_user_id_foreign` FOREIGN KEY (`user_id`) REFERENCES `users` (`id`) ON DELETE SET NULL) (SQL: insert into `posts` (`is_approved`, `created_at`, `discussion_id`, `user_id`, `type`, `ip_address`, `content`, `number`, `is_private`) values (1, 2015-05-30 23:08:34, 160, 73, comment, , Test, 2, 0)) in /var/www/forum/vendor/illuminate/database/Connection.php:664
When migrating threads and posts together with users the threads and the posts will be assigned as created by the user with the
uidfrom myBB which is not the same in flarum if a user was ever deleted in myBB. This can (and in my case) let the migration fail with the following error due to the user not existing in flarum: