Re: Automatically parsing in-line composite types

Hi!

On Tue, Oct 29, 2019 at 9:06 AM Fabio Ugo Venchiarutti
<f(dot)venchiarutti(at)ocado(dot)com> wrote:
> You can use subqueries and array_agg() to deepen your output tree all
> the way to a stack overflow, a single <whatever>_to_json() call at the
> top will recursively traverse and convert whatever you feed it.

Yes, what you are describing is exactly the sad state of things: the
only way to meaningfully retrieve inline composite types which are
made when one aggregate things like that, or when you subselect a set
of fields from a table in a sub-query, is that you then convert the
whole thing to JSON and transmit it in that way. Because this is the
only way you can parse things on the client. Because if you leave it
as raw composite type encoding, you cannot really parse that on the
client correctly in all cases without knowing what types are stored
inside those composite types you are getting.

But JSON is not a lossless transport format: it does not support full
floating point spec (no inf, NANs) and for many types of fields it
just converts to string representation of that, which can be
problematic. For example, if you have binary blobs.

So no, JSON is a workaround, but it is sad that we should have to use
it. PostgreSQL seems to be almost there with the support for composite
types and nested query results, only it seems you cannot really parse
it out. I mean, why PostgreSQL even has its own binary format for
results, then it could just transmit everything as JSON. :-) But that
does not really work for many data types.

I think RowDescription should be extended to provide full recursive
metadata about all data types. That would be the best way to do it.

Mitar

--
http://mitar.tnode.com/
https://twitter.com/mitar_m