Want to use Box for bind? But Type<DB> is not object safe. Here's the solution, use enum

[kingwingfly]

I just want to post a new feature request, however, I found a solution while writing and the feature request is wrong, so I post it here.

I'm trying to define a function, returning Values which is defined as follows:

trait Bind<'q>: Send + Encode<'q, Postgres> + Type<Postgres> {}
type Values<'q> = Vec<Box<dyn Bind<'q>>>;

impl<'q> Encode<'q, Postgres> for Box<dyn Bind<'q>> {}
impl<'q> Type<Postgres> for Box<dyn Bind<'q>> {}
impl<'q, T> Bind<'q> for T where T: Send + Encode<'q, Postgres> + Type<Postgres> {}

So I can define a trait Field having a values method returning Values which can be used to bind on a Query.

pub trait Field {
    /// Return the field names, which will be used in SQL query when insert.
    fn keys(&self) -> Vec<String>;
    /// Return the field values, which matched the keys.
    fn values<'q>(&self) -> Values<'q>;
}

async fn insert<D>(_ctx: &Ctx, mm: &ModelManager, data: D) -> DbResult<i64>
    where
        D: Field,
{
    ....
    let mut q = sqlx::query(&sql);
    for v in data.values() {
        q = q.bind(v);
    }
    let id = q.fetch_one(mm.pgdb()).await?.try_get(0)?;
    Ok(id)
}

However, Type<DB: Database> is not Object safe.

Write until now, I realized that I should use enum to wrap the values I want to insert and match it when bind. But for learning, I post it here, and maybe someone else could refer to this.