Natural values don't fit into an sql database

[NorfairKing]

persistent/persistent/Database/Persist/Sql/Class.hs

Lines 493 to 494 in 6665283

	instance PersistFieldSql Natural where
	sqlType _ = SqlInt64

This fails to round-trip for naturals bigger than a Word64.
I would argue that this instance should be removed.
If you don't need naturals that big, then just use the Word64 instance instead.
If you do, then you expect them to roundtrip.

[parsonsmatt]

Good catch, thanks! Removing the instance seems right, given that we don't provide an instance for Integer and there doesn't appear to be a truly unbounded number type. MySQL supports 65 digits in numeric, and Postgres supports 1000 digits, which are both huge but not infinite.

[hdgarrood]

I think by this argument the Rational instances should be considered for removal, too? Currently Rational is represented as numeric(32,20):

persistent/persistent/Database/Persist/Sql/Class.hs

Lines 490 to 491 in 6d134f7

	instance PersistFieldSql Rational where
	sqlType _ = SqlNumeric 32 20 -- need to make this field big enough to handle Rational to Mumber string conversion for ODBC

but there are lots of rational numbers which can't be represented exactly this way. In particular, anything with more than 20 decimal places, anything with more than 32 significant figures, and also any fraction with a denominator which has prime factors other than 2 or 5 (such as 1/3).

[NorfairKing]

Yes, please remove them too!

[NorfairKing]

You could still have Ratio Int32 maybe..