Re: Emitting JSON to file using COPY TO

On 2023-12-05 Tu 16:02, Joe Conway wrote:
> On 12/5/23 15:55, Andrew Dunstan wrote:
>>
>> On 2023-12-05 Tu 14:50, Davin Shearer wrote:
>>> Hi Joe,
>>>
>>> In reviewing the 005 patch, I think that when used with FORCE ARRAY, 
>>> we should also _imply_ FORCE ROW DELIMITER.  I can't envision a use 
>>> case where someone would want to use FORCE ARRAY without also using 
>>> FORCE ROW DELIMITER.  I can, however, envision a use case where 
>>> someone would want FORCE ROW DELIMITER without FORCE ARRAY, like 
>>> maybe including into a larger array.  I definitely appreciate these 
>>> options and the flexibility that they afford from a user perspective.
>>>
>>> In the test output, will you also show the different variations with 
>>> FORCE ARRAY and FORCE ROW DELIMITER => {(false, false), (true, 
>>> false), (false, true), (true, true)}? Technically you've already 
>>> shown me the (false, false) case as those are the defaults.
>>>
>>>
>>
>> I don't understand the point of FORCE_ROW_DELIMITER at all. There is
>> only one legal delimiter of array items in JSON, and that's a comma.
>> There's no alternative and it's not optional. So in the array case you
>> MUST have commas and in any other case (e.g. LINES) I can't see why you
>> would have them.
>
> The current patch already *does* imply row delimiters in the array 
> case. It says so here:
> 8<---------------------------
> +    <varlistentry>
> + <term><literal>FORCE_ARRAY</literal></term>
> +     <listitem>
> +      <para>
> +       Force output of array decorations at the beginning and end of 
> output.
> +       This option implies the <literal>FORCE_ROW_DELIMITER</literal>
> +       option. It is allowed only in <command>COPY TO</command>, and 
> only
> +       when using <literal>JSON</literal> format.
> +       The default is <literal>false</literal>.
> +      </para>
> 8<---------------------------
>
> and it does so here:
> 8<---------------------------
> +         if (opts_out->force_array)
> +             opts_out->force_row_delimiter = true;
> 8<---------------------------
>
> and it shows that here:
> 8<---------------------------
> + copy copytest to stdout (format json, force_array);
> + [
> +  {"style":"DOS","test":"abc\r\ndef","filler":1}
> + ,{"style":"Unix","test":"abc\ndef","filler":2}
> + ,{"style":"Mac","test":"abc\rdef","filler":3}
> + ,{"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb","filler":4}
> + ]
> 8<---------------------------
>
> It also does not allow explicitly setting row delimiters false while 
> force_array is true here:
> 8<---------------------------
>
> +         if (opts_out->force_array &&
> +             force_row_delimiter_specified &&
> +             !opts_out->force_row_delimiter)
> +             ereport(ERROR,
> +                     (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
> +                      errmsg("cannot specify FORCE_ROW_DELIMITER 
> false with FORCE_ARRAY true")));
> 8<---------------------------
>
> Am I understanding something incorrectly?


But what's the point of having it if you're not using FORCE_ARRAY?


cheers


andrew

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