Greg Sabino Mullane wrote:
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Having found a case where PostgreSQL's composite types might be useful
here, I wonder if support for them could be added to DBD::Pg.
I spent a lot of time today playing with this, and it looks like it would
be possible, although it is going to be quite a bear to code: I got
about 50% there and am going to stop for a while, but thought I should
report back anyway.
While it would be nice to detect custom types "on the fly", we can't:
we first learn about them as we're fetching columns, and it's too late
then to query the system about what the type looks like. So I wrote
a method $dbh->pg_learn_custom_types(). The idea is that you call this
at the top of your script, or you pass something to the connect call that
does it for you first thing.
It does add some overhead, so I'm not comfortable having it automatically
enabled quite yet. This method basically slurps all the custom type
information from the system catalogs and stores in internally in a
C/XS LL struct. When we are fetching and find an unknown type, we walk
the list of custom types to find a match. If we do find one, we make
a temporary sql_info_type struct for it and move on. Then we call a
second internal function for each row, pg_build_hashref(), which recursively
converts the string returned by Postgres into a glorious nest of hashrefs and
arrayrefs. Most of all that is written. What's also needed is the reverse
mapper, to change a bunch of hashrefs into a stringified form to pass to
PQexec and friends, and some minor bind_param hacks.
All rather rough, and the method names will probably change, but that's the
basic plan if anyone wants to comment on it.
Very little API changes, except for the learn() call above and probably an
attribute such as $dbh->{pg_convert_custom_types} which will more than
likely default to on (or should it simply be on after learn() is called?)
We really badly need to get better support into libpq for array and
composite types.
I'm prepared to help if you want to go down that road.
cheers
andrew
