[英]Why does mutably borrowing fix an expected trait implementation?
I am using rust sqlx and I am getting a connection from my DB pool for my query:我正在使用 rust sqlx,并且我正在从我的数据库池获取连接以进行查询:
POOL: OnceCell<Pool<Postgres>> = OnceCell::new();
pub async fn get_connection() -> PoolConnection<Postgres> {
POOL.get().unwrap().acquire().await.unwrap()
}
pub async fn fetch_users() -> Result<Vec<User>> {
let result = sqlx::query_as!(User,
r#"SELECT * FROM users"#)
.fetch_all(get_connection().await).await?;
Ok(result)
}
But get_connection().await
is giving me an error:但是
get_connection().await
给了我一个错误:
the trait bound `sqlx::pool::PoolConnection<sqlx::Postgres>: sqlx::Executor<'_>` is not satisfied expected an implementor of trait `sqlx::Executor<'_>`
The compiler is telling me to fix by using consider mutably borrowing here: `&mut`
which works fine when I change to &mut get_connection().await
.编译器告诉我通过
using consider mutably borrowing here: `&mut`
当我更改为&mut get_connection().await
时效果很好。
I don't understand why this fixes the issue.我不明白为什么这可以解决问题。 Can anyone explain?
谁能解释一下?
Looking at the implementations for sqlx::Executor
, all of them are on some &mut T
type.查看
sqlx::Executor
的实现,它们都属于某种&mut T
类型。 It is implemented for &mut PoolConnection<Postgres>
but not PoolConnection<Postgres>
.它是为
&mut PoolConnection<Postgres>
而不是PoolConnection<Postgres>
实现的。
Adding &mut
changes it from passing a PoolConnection<Postgres>
into a &mut PoolConnection<Postgres>
.添加
&mut
会将其从传递PoolConnection<Postgres>
更改为&mut PoolConnection<Postgres>
。 This is required since Rust does not auto-borrow function parameters.这是必需的,因为 Rust 不会自动借用 function 参数。
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