CODEWITHSUNDEEP
substrate
Sudip Ghimire
Sudip Ghimire

Reputation: 715

Maintain a growing list in offchain storage substrate or use StorageValueRef::mutate in extrensics

I was trying to have a offchain storage that stores a collection of data (likely Vector). And I was assuming to keep this vector growing.

One smooth-seeming approach was to use StorageValueRef::mutate() function but only later that I found we can't use that in extrinsic ( or maybe we could and I am not aware of ).

Another simple approach is to use BlockNumber to create a storage key and use BlockNumber from offchain wroker to reference that value.

But on what I am doing there will be need to store multiple data coming into single block. So I will be restricted to be able to store only one value per block which also doesn't fit the requirements.

Upvotes: 2

Views: 226

Answers (1)

bkchr
bkchr

Reputation: 641

You could create a map like this:

#[pallet::storage]
pub type MyData<T: Config> =
        StorageMap<_, Twox64Concat, T::BlockNumber, Vec<MyData>>;

Then you can do MyData::<T>::append(block_number, data) in your pallet as often as you want.

But I would propose that you introduce some "pruning" window. Let's say 10 and only keep the data of the latest 10 blocks in the state. For that you can just have some MyData::<T>::remove(block_number - 10) in your on_intialize.

But if it is really just about data that you want to set from the runtime for the offchain worker, you could use sp_io::offchain_index::set("key", "data");. But this is a more low level interface. However, here you could also prefix the key by block number to have it unique per block, but you will need to come up with your own custom way of storing multiple values per block.

Upvotes: 2

Related Questions