We will declare a struct with a connection instance inside and add methods over this connection:

pub struct Api {
    conn: PgConnection,
}

The Api struct can be created with the connect method, which uses the DATABASE_URL environment variable to bootstrap a connection to PostgreSQL:

impl Api {
    pub fn connect() -> Result<Self, Error> {
        let database_url = env::var("DATABASE_URL")
            .unwrap_or("postgres://postgres@localhost:5432".to_string());
        let conn = PgConnection::establish(&database_url)?;
        Ok(Self { conn })
    }
}

We use a direct connection here without an r2d2 pool, but you can also make the Api struct compatible with concurrent access. Let's add first the API method for registering new users.