Function fetch_background_info_from_item_id 

pub async fn fetch_background_info_from_item_id(
    conn: &mut SqliteConnection,
    item_id: i64,
) -> Result<Vec<BackgroundInfo>, Error>

アイテムに紐づいた背景情報をアイテムIDから取得します。

SELECT background_info.*
FROM background_info
        LEFT OUTER JOIN rel_background_and_item
                        ON background_info.id = rel_background_and_item.background_info_id
WHERE item_id = ?;