Re: A little confusion about JSON Path

Laurenz Albe schrieb am 17.10.2019 um 13:25:
>> I don't understand why the following two JSON Path expressions aren't doing the same thing in Postgres 12:
>>
>>  jsonb_path_exists(data, '$.k1.list.type() ? (@ == "array")'), -- returns true as expected
>>  jsonb_path_exists(data, '$.k1.list ? (@.type() == "array")') -- returns false - not expected
>>
>> Apparently "@.type()" returns something different then "$.k1.list.type()"
>>
> This seems to be a consequence of "lax" mode:
> 
>  "Besides, comparison operators automatically unwrap their operands in the lax mode,
>   so you can compare SQL/JSON arrays out-of-the-box. An array of size 1 is considered
>   equal to its sole element. Automatic unwrapping is not performed only when:
> 
>   - The path expression contains type() or size() methods that return the type and
>     the number of elements in the array, respectively.
> 
> (from https://www.postgresql.org/docs/12/functions-json.html)
> 
> with sample (data) as (
>   values
>     ('{"k1": {"list":[1,2,3]}}'::jsonb)
> )
> select data,
>        jsonb_path_exists(data, '$.k1.list ? (@.type() == "number")'),       -- lax mode unwraps the array
>        jsonb_path_exists(data, 'strict $.k1.list ? (@.type() == "array")')  -- strict mode doesn't
> from sample;


Ah, thanks. I did not see that part.