On Chain: How can i verify if an account holds a NFT of a particular collection?

Question

I want to build a governance program where only accounts which hold the NFT of a particular collection can vote. How can i check on chain if an accounts holds an NFT of a particular collection. Would this be computationally expensive?

Answer 1

You can fetch the metadata of a mint onchain using mpl_token_metadata crate. Steps to get the collection account on an account :

1. Get the metadata PDA for a mint address

   pub fn get_metadata(mint: Pubkey) -> Pubkey {
   let (metadata, _) = Pubkey::find_program_address(
       &[
           mpl_token_metadata::state::PREFIX.as_bytes(),
           mpl_token_metadata::id().as_ref(),
           mint.as_ref(),
       ],
       &mpl_token_metadata::id(),
   );
    metadata 
   }
   

2. Read the metadata data

   let mint_metadata= Metadata::from_account_info(&ctx.accounts.mint_metadata_address.to_account_info())?; 

3. Check the collection NFT on the mint

    if mint_metadata.collection.is_some() {
               let collection = mint_metadata.collection.unwrap();
               if collection.verified  {
                  // Do your stuff here
               }
           } 

Suggestion - You can store your collection NFT mint address in some global variable (PDA data on a static seed) and then on 3rd step along with the exist check add another check if it belongs to that particular collection or not that you have stored.