pack order into BoxableExpression

[weiznich]

Discussed in #3411

^{Originally posted by mlesin November 15, 2022}
I'm following documentation of BoxableExpression trait, trying to pack dynamically chosen order into BoxableExpression:

    let order_field: Box<dyn BoxableExpression<tasks::table, Pg, SqlType = NotSelectable>> =
        match order.field {
            TasksOrderField::Id => {
                if order.ascending {
                    Box::new(tasks::id.asc())
                } else {
                    Box::new(tasks::id.desc())
                }
            }
            TasksOrderField::Label => {
                if order.ascending {
                    Box::new(tasks::label.asc())
                } else {
                    Box::new(tasks::label.desc())
                }
            }
        };
    query = query.order(order_field);

But this is fails to compile with the following message:

   |
74 |     query = query.order(order_field);
   |                   ^^^^^ the trait `AppearsOnTable<FromClause<tasks::table>>` is not implemented for `dyn BoxableExpression<tasks::table, Pg, SqlType = NotSelectable>`

And I have no idea how to satisfy AppearsOnTable<FromClause<..>> trait because FromClause trait is private.
What am I doing wrong?