Re: Cast jsonb to numeric, int, float, bool

> 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: teodor@sigaev.ru
                                                    WWW: http://www.sigaev.ru/