Custom query for storage

Question

I want to write custom query based on this answer:

impl<T: Config> Pallet<T> {
    pub fn hello_world() -> u128 {
        10
    }
}

But the problem is, it is not exposed in query of pallet inspector in substrate-node-template.

Neither I could query with polkadot js api.

  const queryResHandler = result =>
    result.isNone ? setStatus('None') : setStatus(result.toString()) 
const opts = []
let data = api.query.templateModule.hello_world(...opts, queryResHandler)
or 
let data = api.query.templateModule.helloWorld(...opts, queryResHandler)

Gives error

TypeError: Function.prototype.apply was called on undefined, which is a undefined and not a function

What more I need to do?

Answer 1

As some in the comments mentioned you can create a custom RPC that queries a value from storage.

Check this answer on StackExchange about how to do it or this tutorial, that creates a custom RPC query from the pallet template in the Substrate node template.