PragmaTwice commented on code in PR #5208:
URL: https://github.com/apache/opendal/pull/5208#discussion_r1807737653
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core/src/services/sqlite/backend.rs:
##########
@@ -188,7 +195,27 @@ impl Adapter {
}
}
+#[self_referencing]
+pub struct SqlStream {
+ pool: SqlitePool,
+ query: String,
+
+ #[borrows(pool, query)]
+ #[covariant]
+ stream: BoxStream<'this, Result<String>>,
+}
Review Comment:
The lifetime handling here is a bit tricky.
`sqlx::query_scalar()` and its `.fetch()` heavily depend on lifetime
parameter restrictions:
```rust
pub fn fetch<'e, 'c: 'e, E>(self, executor: E) -> BoxStream<'e, Result<O,
Error>>
where
'q: 'e,
E: 'e + Executor<'c, Database = DB>,
DB: 'e,
A: 'e,
O: 'e,
```
So here to extend the lifetime (since we don't use GAT in our API here e.g.
`type ScanIter<'a>`, in order to be compatible to trait `List` which is also
not a GAT in `Access`.), we need to carry the `Pool` and also the query `&str`
and put it into a self-referencing structure and then we don't need to care the
lifetime checking.
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