Re: Tackling JsonPath support

Hi Pavel,

Can I check a few assumptions about what you're suggesting for this task?

* Our ultimate goal is to give Postgres an implementation of the functions "JSON_EXISTS", "JSON_VALUE", and "JSON_QUERY" which fully comply with the SQL standards.

* The best representation of those standards is found here: [1].

* When [1] mentions a "JSON path expression" or "JSON path language", it's referring to the query language described here: [2].

* Even if other popular DBMS's deviate from [1], or other popular JSONPath implementations deviate from [2], we remain committed to a faithful implementation of [1]. 

* It's okay for my first commit to implement just two things: (a) a PG-internal implementation of JsonPath, and (b) a user-visible implementation of "JSON_QUERY" based on (a).  Later commits could add implementations of "JSON_VALUE", "JSON_EXISTS", etc. in terms of (a).

Thanks,

Christian

[1] http://jtc1sc32.org/doc/N2501-2550/32N2528-WG3-Tutorial-Opening-Plenary.pdf

[2] http://goessner.net/articles/JsonPath

On Fri, Sep 16, 2016 at 2:28 AM, Pavel Stehule <pavel.stehule@gmail.com> wrote:

Hi

2016-09-15 18:05 GMT+02:00 Christian Convey <christian.convey@gmail.com>:

On Mon, Sep 5, 2016 at 1:44 PM, Pavel Stehule <pavel.stehule@gmail.com> wrote:
...

> I wrote XMLTABLE function, and I am thinking about JSON_TABLE function. But
> there is one blocker - missing JsonPath support in our JSON implementation.
>
> So one idea - implement JsonPath support and related JSON query functions.
> This can help with better standard conformance.

Hi Pavel,

Are you still looking for someone to add the JsonPath support to the
JSON implementation?  And if so, how urgently are people waiting for
it?

yes - JsonPath support should be great. I hope so this or next commitfest the XMLTABLE patch will be committed, and with JsonPath I can start to work on JSON_TABLE function.

But the JsonPath can be merged separately without dependency to JSON_TABLE. There are more JSON searching functions, and these functions should to support JsonPath be ANSI SQL compliant.

 

I'd be happy to start working on a patch, but since I'm new to PG
development, I'm probably not the fastest person to get it done.

It is not problem. Probably you should to do this work without deep knowledges about PostgreSQL internals. The work with data types (and functions for data types) is well isolated from PostgreSQL engine.

You can learn from current searching on JSON -  postgresql/src/backend/utils/adt/json.c

And it is good start to be PostgreSQL's hacker - I started with implementation of own data type and related functions.

Regards

Pavel

Kind regards,
Christian