unsaved-changes.md

Changes to collections are not saved

Configuration

• detector id: unsaved-changes
• severity: high

Description

NEAR SDK provides some map collections which can store key-value mappings. You can use get to get a value by its key and insert or overwrite the value by calling insert with a specified key. The collections use borsh to serialize and deserialize, when you want to make some changes to a collection, you need to get an existing value and make changes to it, then insert it into the collection again. Without the insert function, the changes will not be saved to the contract.

Note, since the v4.1.0 of NEAR SDK, developers can use maps in near_sdk::store which will write back changes automatically to avoid this issue introduced by near_sdk::collections.

Sample code

#[allow(unused)]
pub fn modify(&mut self, change: I128) {
    let mut balance = self
        .accounts
        .get(&env::predecessor_account_id())
        .unwrap_or_else(|| env::panic_str("Account is not registered"));

    balance = balance
        .checked_add(change.0)
        .unwrap_or_else(|| env::panic_str("Overflow"));

    // self.accounts
    //     .insert(&env::predecessor_account_id(), &balance);
}

In this sample, balance is a value from self.accounts indexed by the caller's account id, the contract makes some changes to it by calling checked_add. However, the changes are not saved without calling the insert function.