Message-ID: <f22384c9-feda-4e3a-ae3d-1ea5f403d6d9@dunslane.net>
Date: Wed, 4 Sep 2024 16:10:37 -0400
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Subject: Re: json_query conditional wrapper bug
To: Peter Eisentraut <peter@eisentraut.org>,
 pgsql-hackers <pgsql-hackers@postgresql.org>
References: <8022e067-818b-45d3-8fab-6e0d94d03626@eisentraut.org>
 <0919c21e-af83-458b-8e40-1228429eaaa4@eisentraut.org>
From: Andrew Dunstan <andrew@dunslane.net>
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On 2024-09-04 We 6:16 AM, Peter Eisentraut wrote:
> On 28.08.24 11:21, Peter Eisentraut wrote:
>> These are ok:
>>
>> select json_query('{"a": 1, "b": 42}'::jsonb, 'lax $.b' without 
>> wrapper);
>>   json_query
>> ------------
>>   42
>>
>> select json_query('{"a": 1, "b": 42}'::jsonb, 'lax $.b' with 
>> unconditional wrapper);
>>   json_query
>> ------------
>>   [42]
>>
>> But this appears to be wrong:
>>
>> select json_query('{"a": 1, "b": 42}'::jsonb, 'lax $.b' with 
>> conditional wrapper);
>>   json_query
>> ------------
>>   [42]
>>
>> This should return an unwrapped 42.
>
> If I make the code change illustrated in the attached patch, then I 
> get the correct result here.  And various regression test results 
> change, which, to me, all look more correct after this patch.  I don't 
> know what the code I removed was supposed to accomplish, but it seems 
> to be wrong somehow.  In the current implementation, the WITH 
> CONDITIONAL WRAPPER clause doesn't appear to work correctly in any 
> case I could identify.


Agree the code definitely looks wrong. If anything the test should 
probably be reversed:

         wrap = count > 1  || !(
             IsAJsonbScalar(singleton) ||
             (singleton->type == jbvBinary &&
JsonContainerIsScalar(singleton->val.binary.data)));

i.e. in the count = 1 case wrap unless it's a scalar or a binary 
wrapping a scalar. The code could do with a comment about the logic.

I know we're very close to release but we should fix this as it's a new 
feature.


cheers


andrew


--
Andrew Dunstan
EDB: https://www.enterprisedb.com