Add `FromField` instance for `UUID`

[vrom911]

postgresql-simple contains such instance. It would be really helpful to have it here as well.

[sigrlami]

@vrom911 thanks for reporting. I'll take a look into it.

[kmicklas]

Postgres supports UUIDs as a native type, so there is a canonical encoding. SQLite doesn't, so we'd have to decide whether to encode them via the text representation of more compactly as binary blobs. Neither way is going to be best for all use cases.

[danwdart]

I've been using this locally, and I can make it a "pivot" package with only instances, if there's interest:

instance FromField UUID where
    fromField f@(Field (SQLText txt) _) = case fromText txt of
        Just r  -> Ok r
        Nothing -> returnError ConversionFailed f "need a uuid"
    fromField f = returnError ConversionFailed f "need a uuid"

instance ToField UUID where
    toField = SQLText . toText

Or I can pluck the code from #89...

[malteneuss]

As there are basically two valuable encodings (as binary BLOB for performance, and TEXT for human readability in e.g. CLI), would it be possible to add both encodings with BLOB as the default to be fast by default like Postgres and popular Rust libraries like rusqlite do, and a newtype wrapper like TextUUID for textual representations?

Having UUIDv7 soon in haskell-hvr/uuid#87 makes the UUID type even more appealing in databases so that out-of-the-box support would be great.

[jchia]

Unlike Postgresql, sqlite has no UUID type. I'm skeptical about favoring the binary representation over the textual representation or vice versa, so if some change is to be made, I think it makes more sense to have 2 newtype wrappers over UUID. Or at least the default to use should be settable when opening a connection.

[malteneuss]

True, there's no native Sqlite type, but UUID has canonical representations in BLOB or TEXT form (as described in https://www.rfc-editor.org/rfc/rfc9562.html#section-4), which are commonly used with Sqlite , see e.g. https://docs.rs/sqlx/latest/sqlx/sqlite/types/index.html#uuid.

• BLOB has the straight-forward Big-endian Hex-encoding "Saving UUIDs to binary format is done by sequencing all fields in big-endian format"
• TEXT has the common hyphenated format. "The formal definition of the UUID string representation is provided by the following ABNF .... f81d4fae-7dec-11d0-a765-00a0c91e6bf6"

For convenience it would be great to make one of those encodings the default one for the UUID type. I would prefer to make the more performant one (BLOB) the default to have better speeds by default for those that don't care, but either one is fine.