Rust - Cannot Access r2d2 pool connection from Rocket State - rust

Question

I am currently learning Rust and Rocket
Using Rust 1.54.0+Rocket 0.5.0_rc1+ Diesel 1.4.7 + r2d2 0.8.9
I created a DB Postgres connection pool with r2d2. I want to share the connection pool between requests/Routes, to do that I am trying to use Rocket Managed State. https://rocket.rs/v0.5-rc/guide/state/#managed-state
I created a DB Connection Pool, saved it on the state, but when I tried to access that DB Connection Pool from the Route. I am getting 2 error on the same line
Cell<i32> cannot be shared between threads safely
RefCell<HashMap<StatementCacheKey<Pg>, pg::connection::stmt::Statement>> cannot be shared between threads safely
here my code
pub async fn establish_pooled_connection() -> Result<PooledConnection<ConnectionManager<PgConnection>>, r2d2_diesel::Error> {
dotenv().ok();
let database_url = env::var("DATABASE_URL")
.expect("DATABASE_URL must be set");
let manager = ConnectionManager::<PgConnection>::new(&database_url);
let pool = r2d2::Pool::builder().build(manager).expect("Failed to create pool.");
let conn = pool.clone().get().unwrap();
Ok(conn)
}
struct DBPool{
db_pool: PooledConnection<ConnectionManager<PgConnection>>
}
#[rocket::main]
async fn main() {
let pool = establish_pooled_connection();
rocket::build()
.mount("/",routes![callapi])
.manage(DBPool{db_pool: pool})
.launch()
.await.ok();
}
#[post("/callapi", data = "<request>")]
async fn callapi(request: RequestAPI<'_>, _dbpool: &State<DBPool>) -> Json<models::api_response::ApiResponse> {
......
The errors are for this parameter
_dbpool: &State<DBPool>
thanks in advance

Answer 1

Finally, I was able to make this work.
I mostly used this GitHub repo as base
https://github.com/practical-rust-web-development/mystore/tree/v1.1
The repo uses Actix but I am using Rocket.
I think my main miss understanding is that the base PostgreSQL connection is a PGConnection and what you get from the Pool is a PGPooledConnection which at the end is the same.
Here my code
db_connection.rs
use diesel::pg::PgConnection;
use dotenv::dotenv;
use std::env;
use diesel::r2d2::{ Pool, PooledConnection, ConnectionManager, PoolError };
pub type PgPool = Pool<ConnectionManager<PgConnection>>;
pub type PgPooledConnection = PooledConnection<ConnectionManager<PgConnection>>;
//Connects to Postgres and call init pool
pub fn establish_connection() -> PgPool {
dotenv().ok();
let database_url = env::var("DATABASE_URL")
.expect("DATABASE_URL must be set");
init_pool(&database_url).expect("Failed to create pool")
}
//Creates a default R2D2 Postgres DB Pool
fn init_pool(database_url: &str) -> Result<PgPool, PoolError> {
let manager = ConnectionManager::<PgConnection>::new(database_url);
Pool::builder().build(manager)
}
//this functions returns a connection from the Pool
pub fn pg_pool_handler(pool: &PgPool) -> Result<PgPooledConnection, PoolError> {
let _pool = pool.get().unwrap();
Ok(_pool)
}
main.rs
mod db_connection;
use db_connection::{PgPool};
#[rocket::main]
async fn main() {
rocket::build()
.mount("/API",routes![demo])
.manage(db_connection::establish_connection()) //here is where you pass the pool to Rocket state.
.launch()
.await.ok();
}
#[post("/demo", data = "<request>")]
async fn demo _dbpool: &State<PgPool>) -> Json<models::Response> {
let connection = db_connection::pg_pool_handler(_dbpool).unwrap();
let results = users.limit(1)
.load::<User>(&connection)
.expect("Error loading users");
........
That is the basic code, the code can be improved to handle errors in a better way.