On Wed, May 20, 2015 at 8:16 AM, Shulgin, Oleksandr
<oleksandr.shulgin@zalando.de> wrote:
> Hi, Hackers!
>
> Attached is a patch against master to generalize the JSON-producing
> functions in utils/adt/json.c and to provide a set of callbacks which can be
> overridden the same way that is already provided for *parsing* JSON.
>
> The motivation behind this to be able to produce specially-crafted JSON in a
> logical replication output plugin, such that numeric (and bigint) values are
> quoted. This requirement, in turn, arises from the fact that JavaScript
> specification, which is quite natural to expect as a consumer for this JSON
> data, allows to silently drop significant digits when converting from string
> to number object.
>
> I believe this is a well-known problem and I'm aware of a number of tricks
> that might be used to avoid it, but none of them seems to be optimal from my
> standpoint.
>
> I can also imagine this can be used to convert date/time to string
> differently, or adding indentation depending on the depth in object
> hierarchy, etc.
>
> What this patch does apart from providing callbacks, is abstracting most of
> code for producing the correct JSON structure, which was previously
> scattered and repeated in a number of functions with slight differences. In
> the current code there are 5 styles for producing JSON object string,
> differing in whitespace only:
>
> a) no spaces
>
> select to_json(row(1,2));
> to_json
> -----------------
> {"f1":1,"f2":2}
>
> b) some spaces (hstore_to_json)
>
> select hstore(row(1,2))::json;
> hstore
> ------------------------
> {"f1": "1", "f2": "2"}
>
> c) spaces around colon
>
> select json_build_object('f1',1,'f2',2);
> json_build_object
> ----------------------
> {"f1" : 1, "f2" : 2}
>
> d) spaces around colon *and* curly braces
>
> select json_object_agg(x,x) from unnest('{1,2}'::int[]) x;
> json_object_agg
> ----------------------
> { "1" : 1, "2" : 2 }
>
> e) line feeds (row_to_json_pretty)
>
> select row_to_json(row(1,2), true) as row;
> row
> ----------
> {"f1":1,+
> "f2":2}
>
> Personally, I think we should stick to (b), however that would break a lot
> of test cases that already depend on (a). I've tried hard to minimize the
> amount of changes in expected/json.out, but it is quickly becomes cumbersome
> trying to support all of the above formats. So I've altered (c) and (d) to
> look like (b), naturally only whitespace was affected.
Disagree. IMNSHO, the default should be (a), as it's the most compact
format and therefore the fastest. Whitespace injection should be
reserved for prettification functions.
merlin
