Return Vec<Option<Type> with belonging_to

[RubberDuckShobe]

Hello, I have an optional 1-to-1 relation set up between Song and ExtraSongInfo.
When I want to get a single Song's ExtraSongInfo, I can do this and it will return an Option<ExtraSongInfo>:

let extra_info: Option<ExtraSongInfo> = ExtraSongInfo::belonging_to(&song)
    .first(&mut conn)
    .await
    .optional()?;

Now, I want to do this for a Vec<Song>, where songs may not have an ExtraSongInfo associated with them.
So, I tried this:

let extra_info = ExtraSongInfo::belonging_to(&songs)
    .select(ExtraSongInfo::as_select())
    .load(&mut conn)
    .await
    .optional()?;

This, however, returns Option<Vec<ExtraSongInfo>>.
Side note: When I omit .optional(), Visual Studio Code (or rust-analyzer itself?) tries telling me that extra_info is Vec<Option<ExtraSongInfo>>, even though it's actually Vec<ExtraSongInfo>.

How can I actually get Vec<Option<ExtraSongInfo>> where it's None for every song that doesn't have an associated ExtraSongInfo row?

[weiznich]

The correct way to model an 1:1 relation is using a join. For optional 1:1 dependencies that means you want to use left_join().

In this particular case you end up with a query like that:

songs::table.left_join(extra_song_info::table).filter(songs::id.eq_any(song_ids)).select(Option::<ExtraSongInfo>::as_select()).load(&mut conn)?;

See the Relation Guide for more details and information on this topic.

Side note: When I omit .optional(), Visual Studio Code (or rust-analyzer itself?) tries telling me that extra_info is Vec<Option>, even though it's actually Vec.

That's an issue in rust-analyzer, not in diesel. Please report it in their issue tracker, as we cannot do much about it.

[RubberDuckShobe]

That works, thank you!