How can I get all items in a storage map?

Question

How can I get all items in a storage map? In polkadot-js, can we choose a storage map and give no id and its return all items? How can I do it like that?

Answer 1

Actually, the polkadot js did not fetch all the items.

It uses get_keys_paged to get the first <default paged size>(maybe 100) items.

This RPC accepts a key and a start key as params. So, that is how it works. Starting searching the first x items under the given key.

Tips:

After getting all the keys that you want, call get_storage to get the key's value (generally this is a batch call).

You could make a loop like this to fetch all the pairs.

Answer 2

The JavaScript API provides the .keys() and .entries() interfaces on storage. This means -

// returns all the entries, key + value pairs
const entries = await api.query.someWhere.someMap.entries()

// returns the keys only (decoded)
const entries = await api.query.someWhere.someMap.keys()

For a description of the above, you can follow along in the documentation. It is listed here -

• map with keys and entries
• more examples with double-maps

The UI calls .entries() for maps when the option is selected. Underlying in the API it indeed uses the pages keys RPCs to retrieve all keys/entries.

Answer 3

For anyone wondering how to do it in rust for use in the Runtime: You can use the method .iter() of StorageMap combined with the itertools method .collect_vec().

So for example if you wish to get all accounts that hold balance in frame_system::Account, you would do as following:

use itertools::Itertools // imports .collect_vec()
let balances_tuples = frame_system::Account::<ParaRuntime>::iter().collect_vec();