Sqlx, issue with trait bounds for transactions

1

Im trying to extend sqlx Query generically to provide a "finisher" (like execute(), fetch_one(), etc) that will also write a message to an outbox table. The method should take a Transaction, and should reject any other thing that derefs to Executor, since I wan't to be absolutley sure that the original query and the INSERT to my outbox table happens within the same transaction - but I'm running into issues setting up the trait bounds for it.

I've got this:

// ------------------------------------------------------------
// Trait definition
// ------------------------------------------------------------
pub trait Publishable<'q, DB>
where
    DB: Database,
{
    const OUTBOX_INSERT: &'static str = r#"
        INSERT INTO outbox (id, channel, message)
        VALUES ($1, $2, $3, $4)
    "#;

    ///
    async fn outbox_transact<'a>(
        self,
        tx: &'a mut Transaction<'a, DB>,
    ) -> Result<<DB as Database>::QueryResult, sqlx::Error>;
}

// ------------------------------------------------------------
// Geneirc implmentation for Query
// ------------------------------------------------------------
impl<'q, DB, A> Publishable<'q, DB> for Query<'q, DB, A>
where
    DB: Database,
    A: IntoArguments<'q, DB> + Send + 'q,
    for<'c> &'c mut Transaction<'c, DB>: Executor<'c, Database = DB>,
{
    async fn outbox_transact<'a>(
        self,
        tx: &'a mut Transaction<'a, DB>,
    ) -> Result<<DB as Database>::QueryResult, sqlx::Error> {
        self.execute(tx).await
    }
}

Now the above seems to check out at first, but when I try to invoke it on a query like this:

let mut tx = pool.begin().await?;

let query = sqlx::query(
    r#"
        INSERT INTO example (data)
        VALUES ($1)
    "#,
)
.bind(1);

query.outbox_transact(&mut *tx).await?; // <<< compile error here

tx.commit().await?;

Then I run into this compiler error:

error[E0599]: the method `outbox_transact` exists for struct `Query<'_, _, _>`, but its trait bounds were not satisfied
   --> src/outbox/driven.rs:199:15
    |
199 |         query.outbox_transact(&mut *tx).await?;
    |               ^^^^^^^^^^^^^^^ method cannot be called on `Query<'_, _, _>` due to unsatisfied trait bounds
    |
   ::: /home/jakob/.cargo/registry/src/index.crates.io-6f17d22bba15001f/sqlx-core-0.8.2/src/query.rs:17:1
    |
17  | pub struct Query<'q, DB: Database, A> {
    | ------------------------------------- doesn't satisfy `_: Publishable<'_, _>`
    |
note: the following trait bounds were not satisfied:
      `&'c mut Transaction<'c, _>: sqlx::Executor<'c>`
      `<&'c mut Transaction<'c, _> as sqlx::Executor<'c>>::Database = _`
   --> src/outbox/driven.rs:154:42
    |
150 | impl<'q, DB, A> Publishable<'q, DB> for Query<'q, DB, A>
    |                 -------------------     ----------------
...
154 |     for<'c> &'c mut Transaction<'c, DB>: Executor<'c, Database = DB>,
    |                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |                                          |            |
    |                                          |            unsatisfied trait bound introduced here
    |                                          unsatisfied trait bound introduced here
    = help: items from traits can only be used if the trait is implemented and in scope
note: `outbox::driven::Publishable` defines an item `outbox_transact`, perhaps you need to implement it
   --> src/outbox/driven.rs:131:1
    |
131 | pub trait Publishable<'q, DB>
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Then, in trying to fix it I loosen the bounds on the impl to:

for<'c> &'c mut <DB as Database>::Connection: Executor<'c, Database = DB>

...but then I instead get into errors on the call to execute() within my trait impl

error[E0277]: the trait bound `&mut Transaction<'a, DB>: sqlx::Executor<'_>` is not satisfied
   --> src/outbox/driven.rs:160:26
    |
160 |         self.execute(tx).await
    |                          ^^^^^ the trait `sqlx::Executor<'_>` is not implemented for `&mut Transaction<'a, DB>`
    |
    = help: the following other types implement trait `sqlx::Executor<'c>`:
              `&'c mut AnyConnection` implements `sqlx::Executor<'c>`
              `&'c mut MySqlConnection` implements `sqlx::Executor<'c>`
              `&'c mut PgConnection` implements `sqlx::Executor<'c>`
              `&'c mut PgListener` implements `sqlx::Executor<'c>`
              `&'c mut SqliteConnection` implements `sqlx::Executor<'c>`
              `&Pool<DB>` implements `sqlx::Executor<'p>`
note: required by a bound in `sqlx::query::Query::<'q, DB, A>::execute`
   --> /home/jakob/.cargo/registry/src/index.crates.io-6f17d22bba15001f/sqlx-core-0.8.2/src/query.rs:188:12
    |
184 |     pub async fn execute<'e, 'c: 'e, E>(self, executor: E) -> Result<DB::QueryResult, Error>
    |                  ------- required by a bound in this associated function
...
188 |         E: Executor<'c, Database = DB>,
    |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `Query::<'q, DB, A>::execute`

Would be very grateful for any insight on the above, I'm pretty stuck with this.