How to clean a double storage map using primary key?

Question

I have a double storage map.

pub type Schools<T: Config> = StorageDoubleMap<
        _,
        Blake2_128Concat,
        SchoolId,
        Blake2_128Concat,
        StudentId,
        SchoolData<T>,
    >;

With System.killStorage, I am able to delete single entry from this storage after fetching encoded storage key from chain state using primary and secondary key.

How can I delete all entries from this storage in one go?

Answer 1

I don't recommend do this with extrinsic.

This is no way to do this in one OP, it results in O(n) time complexity.

• storage double map key deletion

---

I suggest writing a migration for this.

If the storage is not that large.

• https://paritytech.github.io/polkadot-sdk/master/frame_support/storage/migration/fn.clear_storage_prefix.html

If the storage is large.

• What is the time complexity of StorageMap::clear()?