There are three requirements for applying for a patent for invention and utility model, among which novelty means that the same invention or utility model has not been published in domestic and foreign publications before the application date, has been publicly used in China, or is known to the public in other ways.
You can't apply for invention, you may apply for utility model, but if someone wants to invalidate your patent, you only need to provide evidence that you have been selling it before the filing date, and your patent will be invalid.