Plume/plume-models/src/db_conn.rs

use diesel::{r2d2::{ConnectionManager, CustomizeConnection, Error as ConnError, Pool, PooledConnection}};
#[cfg(feature = "sqlite")]
use diesel::{dsl::sql_query, ConnectionError, RunQueryDsl};
use rocket::{
    http::Status,
    request::{self, FromRequest},
    Outcome, Request, State,
};
use std::ops::Deref;

use Connection;

pub type DbPool = Pool<ConnectionManager<Connection>>;

// From rocket documentation

// Connection request guard type: a wrapper around an r2d2 pooled connection.
pub struct DbConn(pub PooledConnection<ConnectionManager<Connection>>);

/// Attempts to retrieve a single connection from the managed database pool. If
/// no pool is currently managed, fails with an `InternalServerError` status. If
/// no connections are available, fails with a `ServiceUnavailable` status.
impl<'a, 'r> FromRequest<'a, 'r> for DbConn {
    type Error = ();

    fn from_request(request: &'a Request<'r>) -> request::Outcome<Self, Self::Error> {
        let pool = request.guard::<State<DbPool>>()?;
        match pool.get() {
            Ok(conn) => Outcome::Success(DbConn(conn)),
            Err(_) => Outcome::Failure((Status::ServiceUnavailable, ())),
        }
    }
}

// For the convenience of using an &DbConn as an &Connection.
impl Deref for DbConn {
    type Target = Connection;

    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

// Execute a pragma for every new sqlite connection
#[derive(Debug)]
pub struct PragmaForeignKey;
impl CustomizeConnection<Connection, ConnError> for PragmaForeignKey {
    #[cfg(feature = "sqlite")] // will default to an empty function for postgres
    fn on_acquire(&self, conn: &mut Connection) -> Result<(), ConnError> {
        sql_query("PRAGMA foreign_keys = on;").execute(conn)
            .map(|_| ())
            .map_err(|_| ConnError::ConnectionError(ConnectionError::BadConnection(String::from("PRAGMA foreign_keys = on failed"))))
    }
}