Why am I getting an Err(missing field `web3_node_provider`)?

I am new to Rust–confused why I am getting an Err(missing field "web3_node_provider") error when I cargo run using config-rs. Appears to fail at s.try_deserialize()

config.rs

use config::{Config, ConfigError, Environment, File};
use serde::Deserialize;

#[derive(Debug, Deserialize)]
#[allow(unused)]
struct Web3NodeProvider {
    ethereum_mainnet_node_url_http: String,
    alchemy_api_key: String,
}

#[derive(Debug, Deserialize)]
#[allow(unused)]
pub struct Settings {
    web3_node_provider: Web3NodeProvider,
}

impl Settings {
    pub fn new() -> Result<Self, ConfigError> {
        let s = Config::builder()
            .add_source(File::with_name("config/default"))
            .add_source(File::with_name("config/local").required(false))
            .add_source(Environment::with_prefix("app"))
            .build()?;
        s.try_deserialize()
    }
}

main.rs

mod settings;

use settings::Settings;

fn main() {
    let settings = Settings::new();
    println!("{:?}", settings);
}

I’ve pretty much exactly followed the hierarchy example in config-rs, so I’m sure I’m just misunderstanding something basic or missing something. I am able to use "Web3NodeProvider.url" but not "web3_node_provider.ethereum_mainnet_node_url_http".

default.toml

[Web3NodeProvider]
ethereum_mainnet_node_url_http = "https://eth-mainnet.g.alchemy.com/v2/"
alchemy_api_key = "alchemy-api-key"

local.toml

[Web3NodeProvider]
alchemy_api_key = "randomapikey"

>Solution :

I think you have to name your field in config as name of attribute not name of class. Like so:

[web3_node_provider]
ethereum_mainnet_node_url_http = "https://eth-mainnet.g.alchemy.com/v2/"
alchemy_api_key = "alchemy-api-key"