Macro prepare 

macro_rules! prepare {
    (struct $name:ident { $($field:ident : $ty:ty),* $(,)? }) => { ... };
}

prepare! {
    struct ByEmail { email: Text }
}

let query = select((users::id,))
    .from(users::Table)
    .filter(users::email.eq(ByEmail::email()))
    .prepare::<ByEmail, _>(Postgres);

let (sql, params) = query.resolve(ByEmail { email: "a@example.com".into() })?;