Many thanks for your reply. I have built inventory systems using uobjects, structs, maps, arrays. The core concepts are not difficult but Indeed very tedious, because so many moving pieces. But I simply can't use other people's system, especially built in blueprint. For saving, I've also found out it's not easy. I could serialize objects myself and saved it then convert ited back. I can't believe, common game sub systems like inventory is still so hard to build.