Whats the correct way of purging StorageDoubleMap

Question

I`m looking for an efficient way to purge StorageDoubleMap.

so lets assume I have some collection:

#[pallet::storage]
#[pallet::getter(fn provisions)]
pub type Provisions<T: Config> =
    StorageDoubleMap<_, Twox64Concat, T::AccountId, Twox64Concat, TokenId, Balance, ValueQuery>;

That is filled with some data and now I want to remove all the entries effectively.

What I tried so far is:

        #[pallet::weight(T::WeightInfo::claim_rewards())]
        #[transactional]
        pub fn finalize(origin: OriginFor<T>, limit: Option<u32>) -> DispatchResult {
            ensure_root(origin)?;

            let mut remove_counter = 0;

            for prefix in [
                Provisions::<T>::prefix_hash(),
            ] {
                match child::kill_storage(&ChildInfo::new_default_from_vec(prefix), limit) {
                    KillStorageResult::AllRemoved(num_removed) | 
                    KillStorageResult::SomeRemaining(num_removed) => {
                        if let Some(l) = limit {
                            remove_counter+=num_removed;
                            if  remove_counter >= l {
                                Self::deposit_event(Event::PartiallyCleaned);
                                return Ok(().into())
                            }
                        }
                    }
                };
            }
            Self::deposit_event(Event::Cleaned);
             Ok(().into())

        }

but it doesn't seem to work.

Answer 1

StorageDoubleMap has a function:

/// Remove all value of the storage.
pub fn remove_all(limit: Option<u32>) -> sp_io::KillStorageResult {
    <Self as crate::storage::StoragePrefixedMap<Value>>::remove_all(limit)
}

https://crates.parity.io/frame_support/pallet_prelude/struct.StorageDoubleMap.html#method.remove_all

So you can just call let kill_result = Provisions::<T>::remove_all(limit);

Then, check if kill_result is AllRemoved.