Database persistence keeps application data available for later retrieval. A Rust application can connect to PostgreSQL and query it, or use a database to store records beyond the lifetime of a single request. section 4.2 section 4.4.3
In a web application, database persistence supports several parts of the request flow:
- Connect to PostgreSQL and query it from an async Rust program. section 4.2
- Store a posted course, then retrieve a course list or individual course details through web APIs. section 4.4.3
- Retrieve user credentials during sign-in and create, update, or delete records in response to HTTP requests. section 9.1 section 9.8
- Package the database as a container to make it portable across machines and easier to operate with the web service. section 12.3
Listing 4.10 The main() function for iteration 3
use actix_web::{web, App, HttpServer};
use dotenv::dotenv;
use sqlx::postgres::PgPool;
use std::env;
use std::io;
use std::sync::Mutex;
#[path = "../iter3/db_access.rs"]
mod db_access;
#[path = "../iter3/handlers.rs"]
mod handlers;
#[path = "../iter3/models.rs"]
mod models;
#[path = "../iter3/routes.rs"]
mod routes;
#[path = "../iter3/state.rs"]
mod state;
use routes::*;
use state::AppState;
#[actix_rt::main]
async fn main() -> io::Result<()> {
dotenv().ok();
let database_url = env::var("DATABASE_URL").expect(
"DATABASE_URL is not set in .env file");
let db_pool = PgPool::connect(&database_url).await.unwrap();
let shared_data = web::Data::new(AppState { #1
health_check_response: "I'm good. You've already
asked me ".to_string(),
visit_count: Mutex::new(0),
db: db_pool,
});
let app = move || { #2
App::new()
.app_data(shared_data.clone()) #3
.configure(general_routes) #4
.configure(course_routes) #4
};
//Start HTTP server
HttpServer::new(app).bind("127.0.0.1:3000")?.run().await #5
}
The service entry point reads the database URL, connects a PostgreSQL pool, and shares it through application state. section 4.4.3
