How to use Single Map Account BTreeMap anchor solana

Question

I'm following this tutorial (https://solanacookbook.com/guides/account-maps.html#single-map-account) to create an account that store a mapping. But when I run anchor test, the compiler returns

"IdlError: Type not found: {"name":"map","type":{"defined":"BTreeMap<u128,MarketItem>"}}"

This is my code:

pub mod nft {
use super::*;
pub fn init_state(ctx: Context<InitState>) -> Result<()> {
        let authority_account = &ctx.accounts.authority_account;
        let system_program = &ctx.accounts.system_program;
        let state_account = &ctx.accounts.state_account;

        let (state_pda, state_bump) =
            Pubkey::find_program_address(&[b"state".as_ref()], system_program.key);

        if state_pda != *state_account.key
            || !state_account.is_writable
            || !state_account.data_is_empty()
        {
            return Err(error::Error::InvalidStateAccount.into());
        }

        let rent = Rent::get()?;
        let rent_lamports = rent.minimum_balance(State::LEN);

        let create_state_ix = &solana_program::system_instruction::create_account(
            authority_account.key,
            state_account.key,
            rent_lamports,
            State::LEN.try_into().unwrap(),
            system_program.key,
        );

        // msg!("Creating stateAccount account");
        solana_program::program::invoke_signed(
            create_state_ix,
            &[
                authority_account.clone(),
                state_account.clone(),
                system_program.to_account_info(),
            ],
            &[&[b"state".as_ref(), &[state_bump]]],
        )?;

        // msg!("Deserializing MapAccount account");
        let mut program_state =
            solana_program::borsh::try_from_slice_unchecked::<State>(&state_account.data.borrow())
                .unwrap();
        let empty_map: BTreeMap<u128, MarketItem> = BTreeMap::new();

        program_state.map = empty_map;

        // msg!("Serializing MapAccount account");
        program_state.serialize(&mut &mut state_account.data.borrow_mut()[..])?;

        Ok(())
    }
}
#[derive(AnchorSerialize, AnchorDeserialize, Clone)]
pub struct MarketItem {
    item_id: u128,
    nft_contract: Pubkey, // program id,
    token_id: Pubkey,     // ATA
    seller: Pubkey,
    owner: Option<Pubkey>,
    price: u128,
    file_name: String,
    description: String,
    cash_back: u8,
    sold: bool,
    gacha: bool,
    bump: u8,
}

#[derive(AnchorSerialize, AnchorDeserialize, Clone)]
pub struct State {
    pub map: BTreeMap<u128, MarketItem>,
    pub item_ids: u128,
    pub item_sold: u128,
    pub owner: Pubkey,
    pub seed: u64,
}

impl State {
    const LEN: usize = 1 + (4 + (10 * 64));
}

How can I fix this? Thanks

Answer 1

Unfortunately, Anchor/Solana does not support IDL type for BtreeMap.

You can find all available types here: https://www.anchor-lang.com/docs/javascript-anchor-types

The tutorial link given in your question does not saying that it used BTreeMap like what you did, but it's explaining how to achieve Map-like logic in Solana using PDAs.

In your example, you can create a PDA for a MarketItem seeded with item_id and the address of State ensuring it's market from your state account.

However, it would be nicer to have state address stored in MarketItem struct as well so that you can filter markets by state in your offchain logic.