How ActiveRecord::Rollback behaves in nested begin-rescue blocks-CodePudding

I have below code

ActiveRecord::Base.transaction do
  begin
    account.save
    # outer statement
    begin
      user.save
      # inner statement
    rescue StandardError
      raise ActiveRecord::Rollback
    end
  rescue StandardError
    raise ActiveRecord::Rollback
  end
end

If there is an exception in 'inner statement', only 'user' will be rollbacked, right? 'account' won't be rollbacked in that case, isn't it?

CodePudding user response：

In your code there is a single database transaction, and it is all-or-nothing. Rolling back a transaction will roll back all the changes made in that transaction, regardless of where you issue the rollback.

You can nest transactions as well, but be wary that by default transactions are squished together, so even if you add a second transaction inside first transaction:

ActiveRecord::Base.transaction do
  begin
    account.save
    # outer statement
    ActiveRecord::Base.transaction do
      begin
        user.save
        # inner statement
      rescue StandardError
        raise ActiveRecord::Rollback
      end
    end
  rescue StandardError
    raise ActiveRecord::Rollback
  end
end

This will still result in the single transaction, and rollback will cancel all the changes.

To ask for a real subtransaction, you need to add request_new: true to the inner transaction:

ActiveRecord::Base.transaction do
  begin
    account.save
    # outer statement
    ActiveRecord::Base.transaction(require_new: true) do
      begin
        user.save
        # inner statement
      rescue StandardError
        raise ActiveRecord::Rollback
      end
    end
  rescue StandardError
    raise ActiveRecord::Rollback
  end
end

However, at the moment the only database supporting true nested transaction is MS-SQL. Rails at the moment handles this using save points - so don't be confused by the logs.