Not possible to use Array<SomeTuple> as SqlType

[weiznich]

It seems not to be possible to use Array<SomeTuple> as SqlType.

Think of the following query:

select a.*, array_agg(b.*),
from table_a as a 
left join table_b as b on a.id = b.table_a_id
group by a.id

This results in (A::SqlType, Array<B::SqlType>) as SqlType where B::SqlType' is a Tuple (e.g.(BigInt, Text, BigInt)`).

FromSql and FromSqlRow are implemented for Array for each SqlType that has a FromSql implementation. Tuples implement however only FromSqlRow

[sgrif]

We don't currently support tuple types in PG. They're not currently on the list of types that are high priority to support.

[sgrif]

Clearing out old issues....

This is basically just "we don't support PG tuples". I think support for this will probably need to come from another crate. I don't think we can make this ergonomic without variadic generics. If nothing else, the PG type (int4, int4) will map to PgTuple<i32, i32> not (i32, i32) if we ever support it in Diesel.

Closing, as this is not immediately actionable.