Re: GSoC 2015: Extra Jsonb functionality - Mailing list pgsql-hackers
| From | Dmitry Dolgov |
|---|---|
| Subject | Re: GSoC 2015: Extra Jsonb functionality |
| Date | |
| Msg-id | CA+q6zcUuDxB96Zbaa2dGMw1PmxR+PqAVTqUZb-tbn00PG-259Q@mail.gmail.com Whole thread Raw |
| In response to | Re: GSoC 2015: Extra Jsonb functionality (Alvaro Herrera <alvherre@2ndquadrant.com>) |
| Responses |
Re: GSoC 2015: Extra Jsonb functionality
|
| List | pgsql-hackers |
> Perhaph it's my misunderstanding, but this would seem to be more of an intersection operation on keys rather than a delete.
Hm...why? We remove all elements, which are contains in the first and second jsonb ("f": [4, 5] in this case) from the first one.
> Could there be a corresponding jsonb_except function which does the opposite (i.e. returns everything on the left side except where it matches with the right)?
and if I understand your question correctly, this is exactly what the jsonb_delete_jsonb will do, isn't it?.
> Is there a use-case for the example you've given above, where you take JSON containing objects and arrays, and flatten them out into a one-dimensional array?
Hm...actually I don't know about such use-cases. This function is analog of the hstore_to_array (and the similar function hstore_to_matrix), which is used sometimes, judging by github. So I thought this function should be implemented (after this question I'm not so sure).
> What should happen if "g" or {"g"} were used instead?
Did you mean {"g": "key"}? Hmm...but in any case, I suppose this new object should be appended to the array as a regular element.
=# jsonb_add_to_path('{"b": {"c": ["d", "f"]}}'::jsonb, {b, c}::text[], '"g"'::jsonb);
jsonb_add_to_path
---------------------------------------
{"b": {"c": ["d", "f", "g"]}}
> This is a bit strange. Why did "f" get flattened out of "d"?
The main purpose if this function is to get values for required keys from all nesting levels (actually, I thougth it will be not so convenient otherwise and I didn't consider the implementation with path usage). If this so confusing, I can remove this function from the list =)
On 20 March 2015 at 00:08, Alvaro Herrera <alvherre@2ndquadrant.com> wrote:
Thom Brown wrote:
> On 19 March 2015 at 14:35, Alvaro Herrera <alvherre@2ndquadrant.com> wrote:
> > Thom Brown wrote:
> >> On 19 March 2015 at 14:12, Alvaro Herrera <alvherre@2ndquadrant.com> wrote:
> >> > Dmitry Dolgov wrote:
> >> >
> >> >> * jsonb_slice - extract a subset of an jsonb
> >> >> Example of usage:
> Okay, so it pulls it all parents? So I guess you'd get this too:
>
> SELECT jsonb_slice('{"a": 1, "b": {"c": 2}, "d": {"f": 3}, "f":
> 4}'::jsonb, ARRAY['b', 'f', 'x']);
>
> jsonb_slice
> ------------------------------------------------
> {"a": 1, "b": {"c": 2}, "d": {"f": 3}, "f": 4}
Yeah, except "a" wouldn't be output, of course. (The example gets more
interesting if "d" contains more members than just "f". Those would not
get output.)
> >> Although I'm still a bit confused about "f" being produced.
> >
> > I guess you could say that the second argument is an array of element
> > paths, not key names. So to get the result I suggest, you would have to
> > use ARRAY['{b}', '{d,f}', '{x}']. (Hm, this is a non-rectangular
> > array actually... I guess I'd go for ARRAY['b', 'd//f', 'x'] instead, or
> > whatever the convention is to specify a json path).
>
> I think that's where jsquery would come in handy.
If that's what we think, then perhaps we shouldn't accept jsonb_slice at
all because of ambiguous mode of operation.
--
Álvaro Herrera http://www.2ndQuadrant.com/
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