Add FromRow and ToRow traits

[lilac]

Support converting a basic Rust value from and to a PostgresRow instance, so that the insertion and query api would be much cleaner.

For example, instead of

conn.execute("INSERT INTO person (name, time_created, data)
                    VALUES ($1, $2, $3)",
                 [&me.name as &ToSql, &me.time_created as &ToSql,
                  &me.data as &ToSql]);

you write

conn.execute("INSERT INTO person (name, time_created, data)
                    VALUES ($1, $2, $3)", me.toRow());

[sfackler]

You can write that yourself:

impl Person {
    fn to_row<'a>(&'a self) -> [&'a ToSql, ..3] {
        [&self.name as &ToSql, &self.time_created as &ToSql, &self.data as &ToSql]
    }
}

Once rust-lang/rust#11151 lands, It'll be possible to do some interesting ORM-y stuff.

[lilac]

Thanks for the quick response!
Does the current deriving technique support deriving user created traits like "[#deriving(FromRow, ToRow)] struct Person"?

[sfackler]

All derivable traits are currently hardcoded into the compiler. The PR I linked above will allow something like #[derivive_rows] struct Person, but not #[deriving(FromRow, ToRow)] struct Person. We aren't yet sure if we want to make deriving a "special" decorator or not.

[lilac]

Oh, I've found the answer to my question from http://static.rust-lang.org/doc/master/tutorial.html:
The full list of derivable traits is Eq, TotalEq, Ord, TotalOrd, Encodable Decodable, Clone, DeepClone, IterBytes, Rand, Default, Zero, and ToStr.

@sfackler Excellent! That sounds promising!

[sfackler]

I've been thinking about this, and I don't think it's possible to make a reasonable API without creating a fully featured ORM which is beyond the scope of this library.