diesel/
r2d2.rs

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
//! Connection pooling via r2d2.
//!
//! Note: This module requires enabling the `r2d2` feature
//!
//! # Example
//!
//! The below snippet is a contrived example emulating a web application,
//! where one would first initialize the pool in the `main()` function
//! (at the start of a long-running process). One would then pass this
//! pool struct around as shared state, which, here, we've emulated using
//! threads instead of routes.
//!
//! ```rust
//! # include!("doctest_setup.rs");
//! use diesel::prelude::*;
//! use diesel::r2d2::ConnectionManager;
//! # use diesel::r2d2::CustomizeConnection;
//! # use diesel::r2d2::Error as R2D2Error;
//! use diesel::r2d2::Pool;
//! use diesel::result::Error;
//! use std::thread;
//!
//! # #[derive(Copy, Clone, Debug)]
//! # pub struct SetupUserTableCustomizer;
//! #
//! # impl CustomizeConnection<DbConnection, R2D2Error> for SetupUserTableCustomizer
//! # {
//! #     fn on_acquire(&self, conn: &mut DbConnection) -> Result<(), R2D2Error> {
//! #         setup_database(conn);
//! #         Ok(())
//! #     }
//! # }
//!
//! pub fn get_connection_pool() -> Pool<ConnectionManager<DbConnection>> {
//!     let url = database_url_for_env();
//!     let manager = ConnectionManager::<DbConnection>::new(url);
//!     // Refer to the `r2d2` documentation for more methods to use
//!     // when building a connection pool
//!     Pool::builder()
//! #         .max_size(1)
//!         .test_on_check_out(true)
//! #         .connection_customizer(Box::new(SetupUserTableCustomizer))
//!         .build(manager)
//!         .expect("Could not build connection pool")
//! }
//!
//! pub fn create_user(conn: &mut DbConnection, user_name: &str) -> Result<usize, Error> {
//!     use schema::users::dsl::*;
//!
//!     diesel::insert_into(users)
//!         .values(name.eq(user_name))
//!         .execute(conn)
//! }
//!
//! fn main() {
//!     let pool = get_connection_pool();
//!     let mut threads = vec![];
//!     let max_users_to_create = 1;
//!
//!     for i in 0..max_users_to_create {
//!         let pool = pool.clone();
//!         threads.push(thread::spawn({
//!             move || {
//!                 let conn = &mut pool.get().unwrap();
//!                 let name = format!("Person {}", i);
//!                 create_user(conn, &name).unwrap();
//!             }
//!         }))
//!     }
//!
//!     for handle in threads {
//!         handle.join().unwrap();
//!     }
//! }
//! ```
//!
//! # A note on error handling
//!
//! When used inside a pool, if an individual connection becomes
//! broken (as determined by the [R2D2Connection::is_broken] method)
//! then, when the connection goes out of scope, `r2d2` will close
//! and return the connection to the DB.
//!
//! `diesel` determines broken connections by whether or not the current
//! thread is panicking or if individual `Connection` structs are
//! broken (determined by the `is_broken()` method). Generically, these
//! are left to individual backends to implement themselves.
//!
//! For SQLite, PG, and MySQL backends `is_broken()` is determined
//! by whether or not the `TransactionManagerStatus` (as a part
//! of the `AnsiTransactionManager` struct) is in an `InError` state
//! or contains an open transaction when the connection goes out of scope.
//!
//!
//! # Testing with connections pools
//!
//! When testing with connection pools, it is recommended to set the pool size to 1,
//! and use a customizer to ensure that the transactions are never committed.
//! The tests using a pool prepared this way can be run in parallel, because
//! the changes are never committed to the database and are local to each test.
//!
//! # Example
//!
//! ```rust
//! # include!("doctest_setup.rs");
//! use diesel::prelude::*;
//! use diesel::r2d2::ConnectionManager;
//! use diesel::r2d2::CustomizeConnection;
//! use diesel::r2d2::TestCustomizer;
//! # use diesel::r2d2::Error as R2D2Error;
//! use diesel::r2d2::Pool;
//! use diesel::result::Error;
//! use std::thread;
//!
//! # fn main() {}
//!
//! pub fn get_testing_pool() -> Pool<ConnectionManager<DbConnection>> {
//!     let url = database_url_for_env();
//!     let manager = ConnectionManager::<DbConnection>::new(url);
//!
//!     Pool::builder()
//!         .test_on_check_out(true)
//!         .max_size(1) // Max pool size set to 1
//!         .connection_customizer(Box::new(TestCustomizer)) // Test customizer
//!         .build(manager)
//!         .expect("Could not build connection pool")
//! }
//!
//! table! {
//!     users {
//!         id -> Integer,
//!         name -> Text,
//!     }
//! }
//!
//! #[cfg(test)]
//! mod tests {
//!     use super::*;
//!
//!     #[test]
//!     fn test_1() {
//!         let pool = get_testing_pool();
//!         let mut conn = pool.get().unwrap();
//!
//!         crate::sql_query(
//!             "CREATE TABLE IF NOT EXISTS users (id SERIAL PRIMARY KEY, name TEXT NOT NULL)",
//!         )
//!         .execute(&mut conn)
//!         .unwrap();
//!
//!         crate::insert_into(users::table)
//!             .values(users::name.eq("John"))
//!             .execute(&mut conn)
//!             .unwrap();
//!     }
//!
//!     #[test]
//!     fn test_2() {
//!         let pool = get_testing_pool();
//!         let mut conn = pool.get().unwrap();
//!
//!         crate::sql_query(
//!             "CREATE TABLE IF NOT EXISTS users (id SERIAL PRIMARY KEY, name TEXT NOT NULL)",
//!         )
//!         .execute(&mut conn)
//!         .unwrap();
//!
//!         let user_count = users::table.count().get_result::<i64>(&mut conn).unwrap();
//!         assert_eq!(user_count, 0); // Because the transaction from test_1 was never committed
//!     }
//! }
//! ```
pub use r2d2::*;

/// A re-export of [`r2d2::Error`], which is only used by methods on [`r2d2::Pool`].
///
/// [`r2d2::Error`]: r2d2::Error
/// [`r2d2::Pool`]: r2d2::Pool
pub type PoolError = r2d2::Error;

use std::fmt;
use std::marker::PhantomData;

use crate::backend::Backend;
use crate::connection::{
    ConnectionSealed, LoadConnection, SimpleConnection, TransactionManager,
    TransactionManagerStatus,
};
use crate::expression::QueryMetadata;
use crate::prelude::*;
use crate::query_builder::{Query, QueryFragment, QueryId};

/// An r2d2 connection manager for use with Diesel.
///
/// See the [r2d2 documentation](https://docs.rs/r2d2/latest/r2d2/) for usage examples.
#[derive(Clone)]
pub struct ConnectionManager<T> {
    database_url: String,
    _marker: PhantomData<T>,
}

impl<T> fmt::Debug for ConnectionManager<T> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "ConnectionManager<{}>", std::any::type_name::<T>())
    }
}

#[allow(unsafe_code)] // we do not actually hold a reference to `T`
unsafe impl<T: Send + 'static> Sync for ConnectionManager<T> {}

impl<T> ConnectionManager<T> {
    /// Returns a new connection manager,
    /// which establishes connections to the given database URL.
    pub fn new<S: Into<String>>(database_url: S) -> Self {
        ConnectionManager {
            database_url: database_url.into(),
            _marker: PhantomData,
        }
    }

    /// Modifies the URL which was supplied at initialization.
    ///
    /// This does not update any state for existing connections,
    /// but this new URL is used for new connections that are created.
    pub fn update_database_url<S: Into<String>>(&mut self, database_url: S) {
        self.database_url = database_url.into();
    }
}

/// The error used when managing connections with `r2d2`.
#[derive(Debug)]
pub enum Error {
    /// An error occurred establishing the connection
    ConnectionError(ConnectionError),

    /// An error occurred pinging the database
    QueryError(crate::result::Error),
}

impl fmt::Display for Error {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match *self {
            Error::ConnectionError(ref e) => e.fmt(f),
            Error::QueryError(ref e) => e.fmt(f),
        }
    }
}

impl ::std::error::Error for Error {}

/// A trait indicating a connection could be used inside a r2d2 pool
pub trait R2D2Connection: Connection {
    /// Check if a connection is still valid
    fn ping(&mut self) -> QueryResult<()>;

    /// Checks if the connection is broken and should not be reused
    ///
    /// This method should return only contain a fast non-blocking check
    /// if the connection is considered to be broken or not. See
    /// [ManageConnection::has_broken] for details.
    ///
    /// The default implementation does not consider any connection as broken
    fn is_broken(&mut self) -> bool {
        false
    }
}

impl<T> ManageConnection for ConnectionManager<T>
where
    T: R2D2Connection + Send + 'static,
{
    type Connection = T;
    type Error = Error;

    fn connect(&self) -> Result<T, Error> {
        T::establish(&self.database_url).map_err(Error::ConnectionError)
    }

    fn is_valid(&self, conn: &mut T) -> Result<(), Error> {
        conn.ping().map_err(Error::QueryError)
    }

    fn has_broken(&self, conn: &mut T) -> bool {
        std::thread::panicking() || conn.is_broken()
    }
}

impl<M> SimpleConnection for PooledConnection<M>
where
    M: ManageConnection,
    M::Connection: R2D2Connection + Send + 'static,
{
    fn batch_execute(&mut self, query: &str) -> QueryResult<()> {
        (**self).batch_execute(query)
    }
}

impl<M> ConnectionSealed for PooledConnection<M>
where
    M: ManageConnection,
    M::Connection: ConnectionSealed,
{
}

impl<M> Connection for PooledConnection<M>
where
    M: ManageConnection,
    M::Connection: Connection + R2D2Connection + Send + 'static,
{
    type Backend = <M::Connection as Connection>::Backend;
    type TransactionManager =
        PoolTransactionManager<<M::Connection as Connection>::TransactionManager>;

    fn establish(_: &str) -> ConnectionResult<Self> {
        Err(ConnectionError::BadConnection(String::from(
            "Cannot directly establish a pooled connection",
        )))
    }

    fn begin_test_transaction(&mut self) -> QueryResult<()> {
        (**self).begin_test_transaction()
    }

    fn execute_returning_count<T>(&mut self, source: &T) -> QueryResult<usize>
    where
        T: QueryFragment<Self::Backend> + QueryId,
    {
        (**self).execute_returning_count(source)
    }

    fn transaction_state(
        &mut self,
    ) -> &mut <Self::TransactionManager as TransactionManager<Self>>::TransactionStateData {
        (**self).transaction_state()
    }

    fn instrumentation(&mut self) -> &mut dyn crate::connection::Instrumentation {
        (**self).instrumentation()
    }

    fn set_instrumentation(&mut self, instrumentation: impl crate::connection::Instrumentation) {
        (**self).set_instrumentation(instrumentation)
    }

    fn set_prepared_statement_cache_size(&mut self, size: crate::connection::CacheSize) {
        (**self).set_prepared_statement_cache_size(size)
    }
}

impl<B, M> LoadConnection<B> for PooledConnection<M>
where
    M: ManageConnection,
    M::Connection: LoadConnection<B> + R2D2Connection,
{
    type Cursor<'conn, 'query> = <M::Connection as LoadConnection<B>>::Cursor<'conn, 'query>;
    type Row<'conn, 'query> = <M::Connection as LoadConnection<B>>::Row<'conn, 'query>;

    fn load<'conn, 'query, T>(
        &'conn mut self,
        source: T,
    ) -> QueryResult<Self::Cursor<'conn, 'query>>
    where
        T: Query + QueryFragment<Self::Backend> + QueryId + 'query,
        Self::Backend: QueryMetadata<T::SqlType>,
    {
        (**self).load(source)
    }
}

#[doc(hidden)]
#[allow(missing_debug_implementations)]
pub struct PoolTransactionManager<T>(std::marker::PhantomData<T>);

impl<M, T> TransactionManager<PooledConnection<M>> for PoolTransactionManager<T>
where
    M: ManageConnection,
    M::Connection: Connection<TransactionManager = T> + R2D2Connection,
    T: TransactionManager<M::Connection>,
{
    type TransactionStateData = T::TransactionStateData;

    fn begin_transaction(conn: &mut PooledConnection<M>) -> QueryResult<()> {
        T::begin_transaction(&mut **conn)
    }

    fn rollback_transaction(conn: &mut PooledConnection<M>) -> QueryResult<()> {
        T::rollback_transaction(&mut **conn)
    }

    fn commit_transaction(conn: &mut PooledConnection<M>) -> QueryResult<()> {
        T::commit_transaction(&mut **conn)
    }

    fn transaction_manager_status_mut(
        conn: &mut PooledConnection<M>,
    ) -> &mut TransactionManagerStatus {
        T::transaction_manager_status_mut(&mut **conn)
    }
}

impl<M> crate::migration::MigrationConnection for PooledConnection<M>
where
    M: ManageConnection,
    M::Connection: crate::migration::MigrationConnection,
    Self: Connection,
{
    fn setup(&mut self) -> QueryResult<usize> {
        (**self).setup()
    }
}

impl<Changes, Output, M> crate::query_dsl::UpdateAndFetchResults<Changes, Output>
    for PooledConnection<M>
where
    M: ManageConnection,
    M::Connection: crate::query_dsl::UpdateAndFetchResults<Changes, Output>,
    Self: Connection,
{
    fn update_and_fetch(&mut self, changeset: Changes) -> QueryResult<Output> {
        (**self).update_and_fetch(changeset)
    }
}

#[derive(QueryId)]
pub(crate) struct CheckConnectionQuery;

impl<DB> QueryFragment<DB> for CheckConnectionQuery
where
    DB: Backend,
{
    fn walk_ast<'b>(
        &'b self,
        mut pass: crate::query_builder::AstPass<'_, 'b, DB>,
    ) -> QueryResult<()> {
        pass.push_sql("SELECT 1");
        Ok(())
    }
}

impl Query for CheckConnectionQuery {
    type SqlType = crate::sql_types::Integer;
}

impl<C> RunQueryDsl<C> for CheckConnectionQuery {}

/// A connection customizer designed for use in tests. Implements
/// [CustomizeConnection] in a way that ensures transactions
/// in a pool customized by it are never committed.
#[derive(Debug, Clone, Copy)]
pub struct TestCustomizer;

impl<C: Connection> CustomizeConnection<C, crate::r2d2::Error> for TestCustomizer {
    fn on_acquire(&self, conn: &mut C) -> Result<(), crate::r2d2::Error> {
        conn.begin_test_transaction()
            .map_err(crate::r2d2::Error::QueryError)
    }
}

#[cfg(test)]
mod tests {
    use std::sync::mpsc;
    use std::sync::Arc;
    use std::thread;
    use std::time::Duration;

    use crate::r2d2::*;
    use crate::test_helpers::*;

    #[test]
    fn establish_basic_connection() {
        let manager = ConnectionManager::<TestConnection>::new(database_url());
        let pool = Arc::new(Pool::builder().max_size(2).build(manager).unwrap());

        let (s1, r1) = mpsc::channel();
        let (s2, r2) = mpsc::channel();

        let pool1 = Arc::clone(&pool);
        let t1 = thread::spawn(move || {
            let conn = pool1.get().unwrap();
            s1.send(()).unwrap();
            r2.recv().unwrap();
            drop(conn);
        });

        let pool2 = Arc::clone(&pool);
        let t2 = thread::spawn(move || {
            let conn = pool2.get().unwrap();
            s2.send(()).unwrap();
            r1.recv().unwrap();
            drop(conn);
        });

        t1.join().unwrap();
        t2.join().unwrap();

        pool.get().unwrap();
    }

    #[test]
    fn is_valid() {
        let manager = ConnectionManager::<TestConnection>::new(database_url());
        let pool = Pool::builder()
            .max_size(1)
            .test_on_check_out(true)
            .build(manager)
            .unwrap();

        pool.get().unwrap();
    }

    #[test]
    fn pooled_connection_impls_connection() {
        use crate::select;
        use crate::sql_types::Text;

        let manager = ConnectionManager::<TestConnection>::new(database_url());
        let pool = Pool::builder()
            .max_size(1)
            .test_on_check_out(true)
            .build(manager)
            .unwrap();
        let mut conn = pool.get().unwrap();

        let query = select("foo".into_sql::<Text>());
        assert_eq!("foo", query.get_result::<String>(&mut conn).unwrap());
    }

    #[test]
    fn check_pool_does_actually_hold_connections() {
        use std::sync::atomic::{AtomicU32, Ordering};

        #[derive(Debug)]
        struct TestEventHandler {
            acquire_count: Arc<AtomicU32>,
            release_count: Arc<AtomicU32>,
            checkin_count: Arc<AtomicU32>,
            checkout_count: Arc<AtomicU32>,
        }

        impl r2d2::HandleEvent for TestEventHandler {
            fn handle_acquire(&self, _event: r2d2::event::AcquireEvent) {
                self.acquire_count.fetch_add(1, Ordering::Relaxed);
            }
            fn handle_release(&self, _event: r2d2::event::ReleaseEvent) {
                self.release_count.fetch_add(1, Ordering::Relaxed);
            }
            fn handle_checkout(&self, _event: r2d2::event::CheckoutEvent) {
                self.checkout_count.fetch_add(1, Ordering::Relaxed);
            }
            fn handle_checkin(&self, _event: r2d2::event::CheckinEvent) {
                self.checkin_count.fetch_add(1, Ordering::Relaxed);
            }
        }

        let acquire_count = Arc::new(AtomicU32::new(0));
        let release_count = Arc::new(AtomicU32::new(0));
        let checkin_count = Arc::new(AtomicU32::new(0));
        let checkout_count = Arc::new(AtomicU32::new(0));

        let handler = Box::new(TestEventHandler {
            acquire_count: acquire_count.clone(),
            release_count: release_count.clone(),
            checkin_count: checkin_count.clone(),
            checkout_count: checkout_count.clone(),
        });

        let manager = ConnectionManager::<TestConnection>::new(database_url());
        let pool = Pool::builder()
            .max_size(1)
            .test_on_check_out(true)
            .event_handler(handler)
            .build(manager)
            .unwrap();

        assert_eq!(acquire_count.load(Ordering::Relaxed), 1);
        assert_eq!(release_count.load(Ordering::Relaxed), 0);
        assert_eq!(checkin_count.load(Ordering::Relaxed), 0);
        assert_eq!(checkout_count.load(Ordering::Relaxed), 0);

        // check that we reuse connections with the pool
        {
            let conn = pool.get().unwrap();

            assert_eq!(acquire_count.load(Ordering::Relaxed), 1);
            assert_eq!(release_count.load(Ordering::Relaxed), 0);
            assert_eq!(checkin_count.load(Ordering::Relaxed), 0);
            assert_eq!(checkout_count.load(Ordering::Relaxed), 1);
            std::mem::drop(conn);
        }

        assert_eq!(acquire_count.load(Ordering::Relaxed), 1);
        assert_eq!(release_count.load(Ordering::Relaxed), 0);
        assert_eq!(checkin_count.load(Ordering::Relaxed), 1);
        assert_eq!(checkout_count.load(Ordering::Relaxed), 1);

        // check that we remove a connection with open transactions from the pool
        {
            let mut conn = pool.get().unwrap();

            assert_eq!(acquire_count.load(Ordering::Relaxed), 1);
            assert_eq!(release_count.load(Ordering::Relaxed), 0);
            assert_eq!(checkin_count.load(Ordering::Relaxed), 1);
            assert_eq!(checkout_count.load(Ordering::Relaxed), 2);

            <TestConnection as Connection>::TransactionManager::begin_transaction(&mut *conn)
                .unwrap();
        }

        // we are not interested in the acquire count here
        // as the pool opens a new connection in the background
        // that could lead to this test failing if that happens to fast
        // (which is sometimes the case for sqlite)
        //assert_eq!(acquire_count.load(Ordering::Relaxed), 1);
        assert_eq!(release_count.load(Ordering::Relaxed), 1);
        assert_eq!(checkin_count.load(Ordering::Relaxed), 2);
        assert_eq!(checkout_count.load(Ordering::Relaxed), 2);

        // check that we remove a connection from the pool that was
        // open during panicking
        #[allow(unreachable_code, unused_variables)]
        std::panic::catch_unwind(std::panic::AssertUnwindSafe(|| {
            let conn = pool.get();
            assert_eq!(acquire_count.load(Ordering::Relaxed), 2);
            assert_eq!(release_count.load(Ordering::Relaxed), 1);
            assert_eq!(checkin_count.load(Ordering::Relaxed), 2);
            assert_eq!(checkout_count.load(Ordering::Relaxed), 3);
            panic!();
            std::mem::drop(conn);
        }))
        .unwrap_err();

        // we are not interested in the acquire count here
        // as the pool opens a new connection in the background
        // that could lead to this test failing if that happens to fast
        // (which is sometimes the case for sqlite)
        //assert_eq!(acquire_count.load(Ordering::Relaxed), 2);
        assert_eq!(release_count.load(Ordering::Relaxed), 2);
        assert_eq!(checkin_count.load(Ordering::Relaxed), 3);
        assert_eq!(checkout_count.load(Ordering::Relaxed), 3);
        // this is required to workaround a segfault while shutting down
        // the pool
        std::thread::sleep(Duration::from_millis(100));
    }

    #[cfg(feature = "postgres")]
    #[test]
    fn verify_that_begin_test_transaction_works_with_pools() {
        use crate::prelude::*;
        use crate::r2d2::*;

        table! {
            users {
                id -> Integer,
                name -> Text,
            }
        }

        #[derive(Debug)]
        struct TestConnectionCustomizer;

        impl<E> CustomizeConnection<PgConnection, E> for TestConnectionCustomizer {
            fn on_acquire(&self, conn: &mut PgConnection) -> Result<(), E> {
                conn.begin_test_transaction()
                    .expect("Failed to start test transaction");

                Ok(())
            }
        }

        let manager = ConnectionManager::<PgConnection>::new(database_url());
        let pool = Pool::builder()
            .max_size(1)
            .connection_customizer(Box::new(TestConnectionCustomizer))
            .build(manager)
            .unwrap();

        let mut conn = pool.get().unwrap();

        crate::sql_query(
            "CREATE TABLE IF NOT EXISTS users (id SERIAL PRIMARY KEY, name TEXT NOT NULL)",
        )
        .execute(&mut conn)
        .unwrap();

        crate::insert_into(users::table)
            .values(users::name.eq("John"))
            .execute(&mut conn)
            .unwrap();

        std::mem::drop(conn);

        let mut conn2 = pool.get().unwrap();

        let user_count = users::table.count().get_result::<i64>(&mut conn2).unwrap();
        assert_eq!(user_count, 1);
    }
}