How to get StorageDoubleMap keys under a primary key prefix?

[khssnv]

Hello. The types.CreateStorageKey returns an error in an attempt to create a key without secondary key of the StorageDoubleMap specified. Please find a minimal example below.

At the same time state_getKeys method allows to query by pallet name + storage item name for all keys and by pallet name + storage item name + primary key for all secondary keys under the primary key.

How to create a key for querying for all the secondary keys under a specific primary key prefix?

Minimal example.

Querying FRAME pallet-staking pallet, ErasStakers storage item with 1261 era index.

package main

import (
	gsrpc "github.com/centrifuge/go-substrate-rpc-client/v4"
	"github.com/centrifuge/go-substrate-rpc-client/v4/types"
	"github.com/centrifuge/go-substrate-rpc-client/v4/types/codec"
)

func main() {
	api, _ := gsrpc.NewSubstrateAPI("wss://rpc.polkadot.io")
	meta, _ := api.RPC.State.GetMetadataLatest()

	var eraIndex types.U32 = 1261
	bytes, _ := codec.Encode(eraIndex)

	key, err := types.CreateStorageKey(meta, "Staking", "ErasStakers", bytes, nil)
	if err != nil {
		panic(err)
	}
	println(key)
}

Output.

$ go run .
2023/11/16 11:45:32 Connecting to wss://rpc.polkadot.io...
panic: Staking:ErasStakers is a map, therefore requires that number of arguments should exactly match number of hashers in metadata. Expected: 2, received: 1

goroutine 1 [running]:
main.main()
        /example/main.go:18 +0x12e
exit status 2

Keys that works with state_getKeys call.

pallet-staking module: 0x5f3e4907f716ac89b6347d15ececedca
pallet-staking module + ErasStakers method: 0x5f3e4907f716ac89b6347d15ececedca8bde0a0ea8864605e3b68ed9cb2da01b
pallet-staking module + ErasStakers method + 1261 era index primary key: 0x5f3e4907f716ac89b6347d15ececedca8bde0a0ea8864605e3b68ed9cb2da01bba856e6711ab17a6ed040000

[cdamian]

Hi @khssnv,

Please refer to the answers provided in - #300