environment variable `DATABASE_URL` not defined

[haruhinoshana]

hi good evening im new on using diesel i use it with rocket ... i do try to work diesel on rocket but i got
environment variable DATABASE_URL not defined error

heres my code
#![feature(plugin)]
#![plugin(rocket_codegen)]
#[macro_use]
extern crate rocket;
extern crate diesel;
extern crate dotenv;

use diesel::prelude::*;
use diesel::r2d2::{ConnectionManager, Pool, PooledConnection};
use dotenv::dotenv;
use std::env;

// An alias to the type for a pool of Diesel SQLite connections.
type MysqlPool = Pool<ConnectionManager>;

// The URL to the database, set via the DATABASE_URL environment variable.
static DATABASE_URL: &'static str = env!("DATABASE_URL");

/// Initializes a database pool.
fn init_pool() -> Pool {
let manager = ConnectionManager::::new(DATABASE_URL);
Pool::new(manager).expect("db pool");
}

#[get("/")]
fn index() -> &'static str {
"Hello, world!"
}

fn main() {
rocket::ignite()
.manager(init_pool())
.mount("/", routes![index])
.launch();
}

my rust version 1.27.0-nightly (637ac17c5 2018-04-03)

[weiznich]

This error message means that the environment variable DATABASE_URL is not set at compile time. See the documentation of env! for details.