fetch_one using &mut conn as in documentation does not compile

[rschooley]

I am very, very new to Rust and would appreciate a little help with the issue below. I have migrations and fixtures working, but can only get my test to compile using a workaround (more down below).

I am following this page in the docs: https://docs.rs/sqlx/latest/sqlx/attr.test.html

#[cfg(test)]
mod tests {
    use sqlx::{PgPool, Row};

    #[sqlx::test(fixtures("companies"))]
    async fn basic_test(pool: PgPool) -> sqlx::Result<()> {
        let mut conn = pool.acquire().await?;

        let foo = sqlx::query("SELECT * FROM companies")
            .fetch_one(&mut conn)
            .await?;

        assert_eq!(foo.get::<String, _>("name"), "Acme");

        Ok(())
    }
}

The line .fetch_one(&mut conn) has a compiler error:

error[E0277]: the trait bound `&mut sqlx::pool::PoolConnection<Postgres>: Executor<'_>` is not satisfied
   --> src/lib.rs:18:24
    |
18  |             .fetch_one(&mut conn)
    |              --------- ^^^^^^^^^ the trait `Executor<'_>` is not implemented for `&mut sqlx::pool::PoolConnection<Postgres>`
    |              |
    |              required by a bound introduced by this call
    |
    = help: the following other types implement trait `Executor<'c>`:
              <&'c mut PgConnection as Executor<'c>>
              <&'c mut PgListener as Executor<'c>>
              <&'c mut AnyConnection as Executor<'c>>
              <&Pool<DB> as Executor<'p>>
note: required by a bound in `Query::<'q, DB, A>::fetch_one`
   --> /home/robert/.cargo/registry/src/index.crates.io-6f17d22bba15001f/sqlx-core-0.7.1/src/query.rs:213:12
    |
209 |     pub async fn fetch_one<'e, 'c: 'e, E>(self, executor: E) -> Result<DB::Row, Error>
    |                  --------- required by a bound in this associated function
...
213 |         E: Executor<'c, Database = DB>,
    |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `Query::<'q, DB, A>::fetch_one`

I can get this compile (and the test works correctly) if I make this update suggested by Copilot:

.fetch_one(&mut conn as &mut PgConnection)

Playing around a bit more I also got it to compile with this:

.fetch_one(conn.as_mut())

But these don't match the documentation. Did I miss something along the way? Is the as_mut() ok to use or are there issues?

My toml file for reference (I am on nightly):

[package]
name = "rust-sample"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
sqlx = { version = "0.7", features = [
  "macros",
  "migrate",
  "postgres",
  "runtime-tokio",
] }

I tried adding futures (saw it in a video) to see if that was the issue and it didn't resolve it. I also tried the pool: PoolConnection<Postgres> arg for basic_test and also didn't past this.

Aside: having documentation be example based is a great help.

Thanks,
Robert

[paul-hansen]

Looks like this issue is tracking updating that example: #2368

Instead of
&mut conn
Use
&mut *conn