bitsongofficial
SetNFT for existing NFT
In the nft module, the method which allows to save a new NFT (the SetNFT method), performs a search to find any existing NFT with the same ID. If the search produces positive results (find the NFT), the method proceeds by deleting the old one and adding the new one
https://github.com/bitsongofficial/go-bitsong/blob/84691c819214a1f9b9dd844ea2b49b7ccc8ece1b/x/nft/keeper/nft.go#L60-L64
Why do we follow this pattern?
In the fantoken module, during a new FanToken saving procedure, if an existing FanTokein is found, the insertion returns an error
https://github.com/bitsongofficial/go-bitsong/blob/84691c819214a1f9b9dd844ea2b49b7ccc8ece1b/x/fantoken/keeper/fantoken.go#L57-L60
Why do we follow different patterns? Is there any advantage in deleting the old NFT and providing the new one?
Moreover, if we do not need the DeleteNFT method, we can also remove it, since it is only used inside the SetNFT method
https://github.com/bitsongofficial/go-bitsong/blob/84691c819214a1f9b9dd844ea2b49b7ccc8ece1b/x/nft/keeper/nft.go#L78-L88
We delete previous NFT because, it has NFT information as well as NFT by owner keys. When set NFT is called on transfer NFT, only owner field will need to be updated. But if it's used on NFT update, only nft data itself should be updated. To make things put on a single place and can be used multiple times, this is introduced.
What do you mean by NFT update? An NFT is made up of:
type NFT struct {
CollId // Which should never change
MetadataId // Which should never change
Seq // Which should never change
Owner // Which could change
}
IMHO, only the Owner should be able to change for an NFT. If we want to change part of Metadata, this is related to metadata, not NFT directly.
WRT the TransferNFT (which is related to changing the Owner), this would only require deleting the old element from NFTByOwner and adding the new one.
If DeleteNFT is not so used, we could implement the Delete and Set operations on the TransferNFT method.