pool does not live long enough when using AsyncMigrationHarness::new(pool.get().await?)

[DrFlowerkick]

Hi,
during testing I want to create for each test case a test database and migrate my current database setup.

I have the following error message:

error[E0597]: `pool` does not live long enough
   --> db_postgres/tests/postal_address/../common/mod.rs:194:54
    |
192 |           let pool = Pool::builder().build(config).await?;
    |               ---- binding `pool` declared here
193 |           
194 |           let mut harness = AsyncMigrationHarness::new(pool.get().await?);
    |                                                        ^^^^ borrowed value does not live long enough
195 | /         harness
196 | |             .run_pending_migrations(MIGRATIONS)
    | |_______________________________________________- argument requires that `pool` is borrowed for `'static`
...
204 |       }
    |       - `pool` dropped here while still borrowed

Here is my code:

pub async fn new_and_migration() -> Result<Url> {
    let admin_url = url_custom_db("postgres")?;
    let config = AsyncDieselConnectionManager::new(admin_url);
    let pool = Pool::builder().build(config).await?;
    let mut conn = pool.get().await?;

    // Name the DB
    let prefix = std::env::var("TEST_DB_PREFIX").unwrap_or_else(|_| "tst_".into());
    let db_name = format!("{}{}", prefix, uuid::Uuid::new_v4());

    // Connect to admin and create the DB
    create_test_database(&mut conn, &db_name).await?;

    let db_url = url_custom_db(&db_name)?;
    info!(%db_name, %db_url, "Created test database");

    // Run migrations (blocking, but offloaded) against the new DB
    let config = AsyncDieselConnectionManager::new(db_url.clone());
    let pool: Pool<AsyncPgConnection> = Pool::builder().build(config).await?;

    let mut harness = AsyncMigrationHarness::new(pool.get().await?);
    harness
        .run_pending_migrations(MIGRATIONS)
        .map_err(|e| anyhow!("migration failed: {e}"))?;

    Ok(db_url)
}

Any idea what I'm doing wrong?

$ cargo version
cargo 1.90.0 (840b83a10 2025-07-30)

[dependencies]
diesel = { version = "2.3", features = ["postgres", "extras"] }
diesel-async = { version = "0.7", features = ["postgres", "pool", "bb8", "migrations"] }
diesel_migrations = { version = "2.3", features = ["postgres"] }

Running on arch linux.

Regards
Marc

[paolobarbolini]

I don't have my code on me right now to verify, but you may want to try replacing the problematic pool.get() with pool.get_owned()

[weiznich]

The other possible solution is to restrict the scope in that the harness exists to be clearly smaller that the scope the pool exists in. So essentially just wrapping everything that belongs to the migration step into an additional block with {} to enforce dropping the harness earlier

[DrFlowerkick]

Using get_owned() worked for me. I tried using an additional block like this:

    let config = AsyncDieselConnectionManager::new(db_url.clone());
    let pool: Pool<AsyncPgConnection> = Pool::builder().build(config).await?;

    {
        let mut harness = AsyncMigrationHarness::new(pool.get().await?);
        harness
            .run_pending_migrations(MIGRATIONS)
            .map_err(|e| anyhow!("migration failed: {e}"))?;
    }

but this although results in an "pool does not live long enough" message.