AddListings is missing check to prevent duplicate

[0xTranqui]

@iainnash from some initial local UI testing, it looks like addListings is missing a check to prevent duplicate listings from showing up. with the new data structure maybe we can't actually prevent this? would be great if we could, will give it a shot later today

[iainnash]

If we want to use an extra data write to hash the addListings for each listing and check for duplicates we can but does add extra on-chain overhead. Users can delete duplicates or admins can – front-ends can also dedupe.

[0xTranqui]

if we were to prevent dups on front end, do u imagine it looks something like:

• fetch all current listings
• compare new listings to be added to see if they are already included onchain
• prevent txn from being sent if there is a match?

[iainnash]

Yep exactly.