the trait `LoadConnection` is not implemented for `&diesel::PgConnection` - postgresql

Question

I want to create a rest api with rust and can't make it work.
My relevant code so far:
In the main.rs:
#[actix_web::main]
async fn main() -> std::io::Result<()> {
// Loading .env into environment variable.
dotenv::dotenv().ok();
env_logger::init_from_env(env_logger::Env::new().default_filter_or("info"));
// set up database connection pool
let database_url = std::env::var("DATABASE_URL").expect("DATABASE_URL");
let manager = ConnectionManager::<PgConnection>::new(database_url);
let pool: DbPool = r2d2::Pool::builder()
.test_on_check_out(true)
.build(manager)
.expect("Could not build connection pool");
let port = std::env::var("PORT").expect("$PORT is not set.");
HttpServer::new(move || {
App::new()
.app_data(web::Data::new(pool.clone()))
.wrap(middleware::Logger::default())
.route("/", web::get().to(|| async { "Actix REST API" }))
.service(handlers::common::houses::index)
})
.bind(("0.0.0.0", port.parse().unwrap()))?
.run()
.await
}
The schema:
diesel::table! {
houses (id) {
id -> Int4,
user_id -> Varchar,
street -> Varchar,
figure -> Varchar,
floor -> Varchar,
create_date -> Timestamp,
update_date -> Timestamp,
is_deleted -> Bool,
}
}
The model:
#[derive(Debug, Serialize, Deserialize, Queryable)]
pub struct House {
pub id: i32,
pub user_id: String,
pub street: String,
pub figure: String,
pub floor: String,
pub create_date: chrono::NaiveDateTime,
pub update_date: chrono::NaiveDateTime,
pub is_deleted: bool,
}
The handler:
#[get("/houses")]
async fn index(pool: web::Data<DbPool>) -> Result<HttpResponse, Error> {
let houses = web::block(move || {
let conn = &pool.get()?;
find_all(&conn)
})
.await?
.map_err(actix_web::error::ErrorInternalServerError)?;
Ok(HttpResponse::Ok().json(houses))
}
fn find_all(conn: &PgConnection) -> Result<Vec<House>, DbError> {
use crate::schemas::common::houses::houses::dsl::*;
let items =houses.load::<House>(&mut conn)?;
Ok(items)
}
The dependencies are:
[dependencies]
actix-web = "4"
chrono = { version = "0.4.19", features = ["serde"] }
diesel = { version = "2.0.3", features = ["postgres", "r2d2", "chrono"] }
dotenv = "0.15.0"
env_logger = "0.10.0"
serde = { version = "1.0.136", features = ["derive"] }
serde_json = "1.0"`
It keeps giving an error, and I don't understand why.
The error is:
`error[E0277]: the trait bound `&diesel::PgConnection: LoadConnection` is not satisfied src\handlers\common\houses.rs:25:37
| 25 | let items =houses.load::<House>(&mut conn)?;
| ---- -^^^^^^^^
| | | the trait `LoadConnection` is not implemented for `&diesel::PgConnection` help: consider removing the leading `&`-reference required by a bound introduced by this call
| note: required for `table` to implement `LoadQuery<'_, &diesel::PgConnection, House>` note: required by a bound in `diesel::RunQueryDsl::load`
I've seen a similar error with the diesel version 1.4, but I think that this version is different.
Plus I'm starting with rust and I'm a little lost in general at the moment.
I was hopping someone knows what the problem is and how to fix it.

Answer 1

PgConnection implements LoadConnection but &PgConnection does not (note the extra &).
Make conn mutable and pass as a mutable reference:
#[get("/houses")]
async fn index(pool: web::Data<DbPool>) -> Result<HttpResponse, Error> {
let houses = web::block(move || {
let mut conn = pool.get()?; // <------------
find_all(&mut conn) // <------------
})
.await?
.map_err(actix_web::error::ErrorInternalServerError)?;
Ok(HttpResponse::Ok().json(houses))
}
fn find_all(conn: &mut PgConnection) -> Result<Vec<House>, DbError> {
// ^^^ <------------
use crate::schemas::common::houses::houses::dsl::*;
let items = houses.load::<House>(conn)?; // <------------
Ok(items)
}