GraphQL 当有人触发购买事件时，更新一个新的ItemBought对象，更新activeItem产生新买家，这不会从activeItem中删除，update with a new buyer 当有人取消事件时，更新activeItem中买家为死地址，以此判断item被取消
Build completed: Qme8dwbjRFfXEBmw87ZxpmmrhubL3cekycdceTdFZbiTuL
Deployed to https://thegraph.com/studio/subgraph/nft-marketplace
Subgraph endpoints: Queries (HTTP): https://api.studio.thegraph.com/query/53377/nft-marketplace/v0.0.1