Do I need an invitation letter to visit my boyfriend who is a teacher?

Hi, my boyfriend teaches in an international school in Tianjin. I plan to visit over christmas and have my ticket & travel insurance all sorted. I have filled in the application form online but there is no list of criteria that is required to bring with you. I am ready to book my appointment at the application centre and just want to be sure I do not need an invitation letter from him, or copies of his visa and accommodation too??? I am unsure and want to be certain as I will have to take time off from work to put the application in.