Iden all columns

[Sytten]

Motivation

I am reviving #90 because I had time to mature our solution and I think it is relevant to the general community.
Almost all our Iden look like:

use sea_query::Iden;

#[derive(Iden, Clone)]
pub enum Responses {
    Table,
    Id,
    StatusCode,
    Raw,
    Length,
    RoundtripTime,
    CreatedAt,
}

impl Responses {
    pub fn all_table_columns() -> Vec<(Responses, Responses)> {
        vec![
            (Responses::Table, Responses::Id),
            (Responses::Table, Responses::StatusCode),
            (Responses::Table, Responses::Raw),
            (Responses::Table, Responses::Length),
            (Responses::Table, Responses::RoundtripTime),
            (Responses::Table, Responses::CreatedAt),
        ]
    }

    pub fn all_columns() -> Vec<Responses> {
        vec![
            Responses::Id,
            Responses::StatusCode,
            Responses::Raw,
            Responses::Length,
            Responses::RoundtripTime,
            Responses::CreatedAt,
        ]
    }
}

This is super useful for query building because you have a central place to change if you add a new column to your table.
Both methods needed since sometimes you can't specify a table name (like in a CTE scenario), but most of the time you want to specify the table name.

Proposed Solutions

I think we should add a way to generate those methods or a variant of them with the Iden macro.
Or maybe it could be another macro like IdenIter.

I would also try to get rid of the Vec if possible and maybe even add some helpers on the Iterator.
I could see something like Responses::all_columns().except(Responses::Length)

Additional Information

I tried EnumIter but it really it not as convenient because of the need to add the table name.

[tyt2y3]

I think this is doable in SeaORM, because it is shipping it's own version of DeriveIden SeaQL/sea-orm#1740

[Sytten]

This particular project doesn't pull sea-orm (it's a combination of diesel and sea-query). Worst case I can create another crate for this macro.

[tyt2y3]

If we put this inside sea-query, may be we can have a new macro, may be IdenIter / IdenList. And the methods can probably look like:

fn iter_columns() -> impl Iterator<Item = Self> {
    ..
}

fn all_columns() -> Vec<Self> {
    Self::iter_columns().collect()
}