Can't override nested settings

[sedrik]

Given a Config structure like

#[derive(serde::Deserialize, Debug)]
pub struct Settings {
    pub authentication_url: String,
    pub database: DatabaseSettings,
}

#[derive(serde::Deserialize, Debug)]
pub struct DatabaseSettings {
    pub host: String,
}

And the following config setup

    let config = Config::builder()
        .add_source(config::File::from(
            configuration_directory.join("base.yaml"),
        ))
        .add_source(config::Environment::with_prefix("APP"));

I am able to use APP_AUTHENTICATION_URL to override settings.authentication_url but when I try APP_DATABASE_HOST my customization is not detected. Is there something special I need to do to allow env overrides for nested configs?

Using the following entry in Cargo.toml

config = "0.13.0"

[szarykott]

It is more of an educated guess and quick look at env.rs, but did you try something like APP_DATABASE.HOST?

[kjaleshire]

It's non-obvious but you must explicitly set the separator, otherwise the environment source won't attempt to break up the key into nested components:

std::env::set_var("APP_DATABASE_HOST", "postgres://foo.url");

let config = Config::builder()
    .add_source(config::File::from(
        configuration_directory.join("base.yaml"),
    ))
    .add_source(config::Environment::with_prefix("APP").separator("_"))
    .try_deserialize()
    .unwrap();

println!("{}", config.database.host);
// # postgres://foo.url

[kjaleshire]

@szarykott or @mehcode , is there a reason nesting is impossible using env vars by default?

[matthiasbeyer]

It seems to me that the env-var stuff makes more problems than it solves. :cry:

[sedrik]

Ah, setting the separator did indeed solve it.

While the env overwrite logic complicates things it is really nice for running the same docker in different envs.

Thanks for the support, it's a great library to use :heart: