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* JSONpath query that returns paths to the matches
@ 2021-12-16 15:56 Alex R <[email protected]>
2021-12-16 16:08 ` Re: JSONpath query that returns paths to the matches David G. Johnston <[email protected]>
0 siblings, 1 reply; 3+ messages in thread
From: Alex R @ 2021-12-16 15:56 UTC (permalink / raw)
To: [email protected]
Hi,
I am trying to figure out whether Postgres 14 allows me to find the paths
to certain values in the JSON, rather than the values themselves. To
illustrate, here is a test query:
SELECT JSONB_PATH_QUERY($${
"this": "that",
"that": [{"x": "aaa"},{"y": "missed"}],
"nested": {
"deep": {
"x": "bbb"
}
}
}$$, 'strict $.**."x"');
It returns 2 matches: "aaa" and "bbb". However, what I'd like to get
instead is 2 paths that point to the matches, i.e.,:
- $.that[0]
- $.nested.deep
Can this be accomplished using means that are available out of the box? If
not, what would be a sane way of implementing it?
Thank you for your help,
Alex
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: JSONpath query that returns paths to the matches
2021-12-16 15:56 JSONpath query that returns paths to the matches Alex R <[email protected]>
@ 2021-12-16 16:08 ` David G. Johnston <[email protected]>
2021-12-20 00:19 ` Re: JSONpath query that returns paths to the matches Alex R <[email protected]>
0 siblings, 1 reply; 3+ messages in thread
From: David G. Johnston @ 2021-12-16 16:08 UTC (permalink / raw)
To: Alex R <[email protected]>; +Cc: pgsql-novice <[email protected]>
On Thu, Dec 16, 2021 at 8:57 AM Alex R <[email protected]> wrote:
> It returns 2 matches: "aaa" and "bbb". However, what I'd like to get
> instead is 2 paths that point to the matches, i.e.,:
> - $.that[0]
> - $.nested.deep
>
> Can this be accomplished using means that are available out of the box? If
> not, what would be a sane way of implementing it?
>
1. Not that I can see documented.
2a See if some other language that has a PL extension for PostgreSQL can do
this more easily and write a function in the language.
2b Create a custom C language function based off of one of the existing
"path exists" functions that keeps track of its position in the graph and
the returns that instead of a boolean/whatever.
2c Create your own procedural code, which can be done in pl/pgsql, that
performs the graph traversal and captures the data like in 2b.
David J.
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: JSONpath query that returns paths to the matches
2021-12-16 15:56 JSONpath query that returns paths to the matches Alex R <[email protected]>
2021-12-16 16:08 ` Re: JSONpath query that returns paths to the matches David G. Johnston <[email protected]>
@ 2021-12-20 00:19 ` Alex R <[email protected]>
0 siblings, 0 replies; 3+ messages in thread
From: Alex R @ 2021-12-20 00:19 UTC (permalink / raw)
To: pgsql-novice <[email protected]>
Hi David,
Thank you for the swift reply. After ruling out the option of doing that by
leveraging JSONPath, I took a different approach and wrote a function
in pl/pgsql
that does not need these paths at all. I could deviate a bit, because I had
some wiggle room in the context of the bigger problem I was working on.
For others who might be confronted with a similar problem in the future,
here is a minimal example that uses Python and a library called jsonpath_ng,
which tells you what the match is and where it occurs:
```
# pip install jsonpath_ng
import json
from jsonpath_ng import jsonpath, parse
raw = '''{
"this": "that",
"that": [{"x": "aaa"},{"y": "missed"}],
"nested": {
"deep": {
"x": "bbb"
}
}
}'''
data = json.loads(raw)
query = parse('$..x')
results = query.find(data)
for entry in results:
print(f'{entry.full_path} -> {entry.value}')
# that.[0].x -> aaa
# nested.deep.x -> bbb
```
Porting this to pl/python is left as an exercise for the reader :-)
^ permalink raw reply [nested|flat] 3+ messages in thread
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2021-12-16 15:56 JSONpath query that returns paths to the matches Alex R <[email protected]>
2021-12-16 16:08 ` David G. Johnston <[email protected]>
2021-12-20 00:19 ` Alex R <[email protected]>
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