Query chain for types in a storagemap

Question

I want to get the meta function description of pallets storage maps. Returning an output like this:

{ Twox64Concat, [u8; 16], u32 } = query.storagemap(pallet: "template", storagemap: "SomeMap")

This is a storage map I created and spun up the substrate node template:

#[pallet::storage]
pub(super) type SomeMap<T: Config> = StorageMap<_, Twox64Concat, [u8; 16], u32>;

The metadata only gives limited information about the storage map:

              {
                name: SomeMap
                modifier: Optional
                type: {
                  Map: {
                    hashers: [
                      Twox64Concat
                    ]
                    key: 111
                    value: 4
                  }
                }
                fallback: 0x00
                docs: []
              }
            ]
          }

I'm trying to get the function input types,

The only type information I'm able to gathered is what polkadot.js gives me:

Thanks!
~ flipchan

Answer 1

There is also a type map in the metadata.

Something like this:

 metadata: {
    V14: {
      lookup: {
        types: [
          {
            id: 0
            type: {
              path: [
                account
                AccountId20
              ]
              params: []
              def: {
                Composite: {
                  fields: [
                    {
                      name: null
                      type: 1
                      typeName: [u8; 20]
                      docs: []
                    }
                  ]
                }
              }
              docs: []
            }
          }

You need to follow the type id to construct the type base on that map to get the real type.

E.G. this is my chain's [u8; 16] which is located at 105:

{
  name: Array16
  fields: [
    {
      name: null
      type: 105
      typeName: [u8; 16]
      docs: []
    }
  ]
  index: 4
  docs: []
}
{
  id: 105
  type: {
    path: []
    params: []
    def: {
      Array: {
        len: 16
        type: 2
      }
    }
    docs: []
  }
}

---

In simple terms, find the storage, find the type id then construct the type.