Re: json casts

On 05/27/2014 03:57 PM, Heikki Linnakangas wrote:
> On 05/27/2014 10:53 PM, Andrew Dunstan wrote:
>> I've been on the receiving end of a couple of mumbles about the fact
>> that the JSON rendering code ignores casts of builtin types to JSON.
>> This was originally done as an optimization to avoid doing cache lookups
>> for casts for things we knew quite well how to turn into JSON values
>> (unlike, say, hstore). However, there is at least one concrete case
>> where this has some possibly undesirable consequences, namely
>> timestamps. Many JSON processors, especially JavaScript/ECMAScript
>> processors, require timestamp values to be in ISO 8601 format, with a
>> 'T' between the date part and the time part, and thus they barf on the
>> output we produce for such values.
>
> I don't understand what ignoring casts of builtin types to JSON means. 
> Can you give an example?


See src/backend/utils/adt/json.c:json_categorize_type() lines 1280-1300.

When rendering some value as part of a json string, if a cast exists 
from the data type to json, then the cast function is used to render the 
json instead of the type's normal output function, but only if it's not 
a builtin type.

cheers

andrew