mysql - Error querying database using Diesel, r2d2, and r2d2-diesel -

i've set system using connection pooling system utilizing diesel, r2d2, , r2d2-diesel serve api host web application. i've been following blog post basis has helped me set things up. however, i've made modification of switching mysql database backend; i've added necessary diesel features , assumed wouldn't issue.

here's code use set connection pool (very same blog post):

use diesel::prelude::*; use diesel::mysql::mysqlconnection; use r2d2::{ gettimeout, pool, pooledconnection, config }; use r2d2_diesel::connectionmanager;  pub struct db(pooledconnection<connectionmanager<mysqlconnection>>);  impl db {     pub fn conn(&self) -> &mysqlconnection {         &*self.0     } }  pub fn create_db_pool() -> pool<connectionmanager<mysqlconnection>> {     let config = config::default();     let manager = connectionmanager::<mysqlconnection>::new(format!("{}", db_credentials));     pool::new(config, manager).expect("failed create pool.") } 

i've been encountering issue during process of setting database interface system. when make query database through diesel, following error: err(databaseerror(__unknown, "commands out of sync; can\'t run command now"))

i've done research , seems error occurs when previous query hasn't been read before sending another, leading me believe may library error. checked mysql query log, , see no queries @ other creating connections in connection pools.

i've reduced error down test case. following responds error message pasted above:

/// make sure can run basic queries on database using connection pool #[test] fn basic_queries() {     use diesel::connection::simpleconnection;      let mut pool = create_db_pool();     let mut conn = pool.get().unwrap();     let res = conn.batch_execute("select 1");     println!("{:?}", res); } 

the same error message produced running query following, that's more difficult reduce single test case:

let query = diesel::insert(&beatmap).into(schema::beatmaps::dsl::beatmaps); // println!("{:?}", query); print_sql!(query); let conn: &mysqlconnection = &*client.pool.get().expect("unable connection pool"); let res = query.execute(conn); 

i'd think implementation error on part, possible has database configuration? database i'm using development in active use on 3 languages , several applications without issue, doubt it.

edit: has been fixed in latest versions of involved crates.

it turns out r2d2-diesel library is broken mysql. health check makes query never reads result out messes mysql command ordering user-made queries.

i made fork of r2d2-diesel repository fixes issue. not designed long-term solution , only works mysql clients. if you'd use it, add following cargo.toml:

r2d2-diesel-mysql = { git = "https://github.com/ameobea/r2d2-diesel" } 

change instances of r2d2_diesel r2d2_diesel_mysql in codebase , should work drop-in replacement.