Consider `#[derive(QueryAll)]`

[sgrif]

Not sold on the name. We should come up with a better one.

A question that periodically comes up is "my Queryable struct uses all but one column from my table. How do I do this?"

In crates.io we have the following:

/// We literally never want to select `textsearchable_index_col`
/// so we provide this type and constant to pass to `.select`
type AllColumns = (
    crates::id,
    crates::name,
    crates::updated_at,
    crates::created_at,
    crates::downloads,
    crates::description,
    crates::homepage,
    crates::documentation,
    crates::readme,
    crates::readme_file,
    crates::license,
    crates::repository,
    crates::max_upload_size,
);

pub const ALL_COLUMNS: AllColumns = (
    crates::id,
    crates::name,
    crates::updated_at,
    crates::created_at,
    crates::downloads,
    crates::description,
    crates::homepage,
    crates::documentation,
    crates::readme,
    crates::readme_file,
    crates::license,
    crates::repository,
    crates::max_upload_size,
);

impl Crate {
    pub fn all() -> diesel::dsl::Select<crates::table, AllColumns> {
        crates::table.select(ALL_COLUMNS)
    }
}

This seems like a reasonable pattern to derive in Diesel. I'd want to pull this into a trait though so the type and constant can become an associated type and associated constant. I think I'd also want to call them UsedColumns.