Add like, not_like and concat for PostgreSQL Bytea

[Justice4Joffrey]

I saw a couple of issues requestinhg support for this (e.g. #3127).

This is mostly a copy of TextExpressionMethods.

Would love to know if there's a more concise way of creating a Vec<u8> from a readable literal other than "S%".as_bytes().to_owned()).

[Mingun]

I believe, the shortest way is b"S%".to_vec()

[weiznich]

Thanks for opening this PR 👍

The implementation itself looks good. I would like to see a compile test that demonstrates that code using like/concat/not_like with a binary column only compiles using a postgres connection.

[Justice4Joffrey]

In the current implementation, all of these pg-specific expression methods will be available for all T's when the "postgres_backend" feature flag is set. Probably works in practice but is clearly incorrect.

E.g.

impl<T> PgTextExpressionMethods for T
where
    T: Expression,
    T::SqlType: TextOrNullableText,
{
}

[weiznich]

That's what I assumed 😉.

So the correct way to fix this is to introduce postgres specific variants of the corresponding operators. It should be easy to define them via the diesel::infix_operation! macro.

[Justice4Joffrey]

Ok I see. I think the take-home here is you should never return a type other than those defined in pg/helper_types.rs, and those should only refer to pg specific operators.

IMO it would be good to make that slightly more obvious. All methods in that file specifically use helper_types through the crate-level dsl module, which is misleading.

[weiznich]

Thanks for the update 👍

Yes that requirement could made more clear. I would definitively accept a PR adding corresponding comments. Otherwise I try to remember that and will add a comment there myself as soon as I touch that part of the code again.