I would like to complain about this patch. First, I think that it
would've been a better idea to use functions for this rather than
operators, because now ::text does something totally unlike what ::int
does, and that's confusing. If we had json_to_WHATEVER for various
values of WHATEVER then all of the conversions could be spelled
similarly; as the commit message right points out, the cast can only
do one thing.
From another point of view, casting jsonb to text produces completely grounded
result: we get a text correctly formatted as json. Other casts produce correct
json but with non-text type.
Casting jsonb with text is two-way casting:
# select '123'::jsonb::text::jsonb, '"xxx"'::jsonb::text::jsonb;
jsonb | jsonb
-------+-------
123 | "xxx"
But casting with numeric types and bool is not, but it could be done with
intermediate cast to text (uppercase cast):
# select '123'::jsonb::int::TEXT::jsonb;
jsonb
-------
123
For completeness it's possible to add direct cast from numeric/boolean types to
jsonb. Then such casts will be mutual.
Also, I think the error messages aren't great:
+select '[]'::jsonb::bool;
+ERROR: jsonb value must be boolean
In this simple scenario, it's clear enough what has gone wrong, but in
a more complicated case I suspect people will have a hard time
figuring out what the source of that error message is. It seems like
it would be better to say something about casting or converting in the
error message, to give users a clue.
Agree, something like "could not convert jsonb value to boolean type. jsonb
value must be scalar boolean type"?
--
Teodor Sigaev E-mail: teo...@sigaev.ru
WWW: http://www.sigaev.ru/
