On 07.01.2018 00:11, Pavel Stehule wrote:
2018-01-06 22:02 GMT+01:00 Oleg Bartunov <obartu...@gmail.com
<mailto:obartu...@gmail.com>>:
On Sat, Jan 6, 2018 at 8:22 AM, Pavel Stehule
<pavel.steh...@gmail.com <mailto:pavel.steh...@gmail.com>> wrote:
> Hi
>
> I am checking the JSONPath related code
>
> Questions, notes:
>
> 1. jsonpath operators are not consistent with any other .. json,
xml .. I am
> missing ?, @> operátors
I have slides about jsonpath
http://www.sai.msu.su/~megera/postgres/talks/sqljson-pgconf.eu-2017.pdf
<http://www.sai.msu.su/%7Emegera/postgres/talks/sqljson-pgconf.eu-2017.pdf>
> 2. documentation issue - there is "'{"a":[1,2,3,4,5]}'::json *?
'$.a[*] ? (@
>> 2)'" - operator *? doesn't exists
There are should be @? operator
> 3. operator @~ looks like too aggressive shortcut - should be better
> commented
>
> What is not clean, if jsonpath should to create some new
operators for json,
> jsonb types? It is special filter, defined by type, so from my
perspective
> the special operators are not necessary.
It's impossible to distinguish jsonpath from text, so introducing
new operators
are easier than everytime explicitly specify jsonpath datatype.
There are two possible solutions - special operator or explicit
casting. In this case I am not sure if special operator for this case
is good solution. Probably nobody will use it - because there SQL/JSON
functions, but I don't think so this inconsistency is correct.
I have not strong opinion about it - it will be hidden feature for
almost all users.
Operators are necessary for index support now.
Operators allows us to use a more concise syntax in simple cases, when
we extract JSON item(s) without error handling:
js @* '$.key'
vs
JSON_QUERY(js, '$.key' RETURNING jsonb ERROR ON ERROR)
Also @* оperator gives us ability to extract a set of JSON items.
JSON_QUERY can only wrap extracted item sequence into JSON array which
we have to unwrap with our json[b]_array_elements() function. I also
thought about returning setof-types in JSON_VALUE/JSON_QUERY:
JSON_QUERY(jsonb '[1,2,3]', '$[*]' RETURNING SETOF jsonb)
But it is not so easy to implement now, because we should introduce new
node like TableFunc (or also we can try to use existing JSON_TABLE
infrastructure).
Set-returning expressions are not allowed in every context, so for
returning singleton items there should be additional operator.
--
Nikita Glukhov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company
