From: | Andrew Dunstan <andrew(at)dunslane(dot)net> |
---|---|
To: | Joe Conway <mail(at)joeconway(dot)com>, Davin Shearer <davin(at)apache(dot)org>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Emitting JSON to file using COPY TO |
Date: | 2023-12-05 21:12:00 |
Message-ID: | 22d9e40d-7de2-1301-3970-16136f7732a6@dunslane.net |
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Lists: | pgsql-general pgsql-hackers |
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
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