Extension for PostgreSQL cast jsonb to hstore WIP

On 2024-04-02 Tu 07:07, ShadowGhost wrote:

Hello all.
Recently, when working with the hstore and json formats, I came across
the fact that PostgreSQL has a cast of hstore to json, but there is no
reverse cast. I thought it might make it more difficult to work with
these formats. And I decided to make a cast json in the hstore. I used
the built-in jsonb structure to create it and may have introduced
methods to increase efficiency by 25% than converting the form
jsonb->text->hstore. Which of course is a good fact. I also wrote
regression tests to check the performance. I think this extension will
improve the work with jsonb and hstore in PostgreSQL.
If you've read this far, thank you for your interest, and I hope you
enjoy this extension!

One reason we don't have such a cast is that hstore has a flat
structure, while json is tree structured, and it's not always an object
/ hash. Thus it's easy to reliably cast hstore to json but far less easy
to cast json to hstore in the general case.

What do you propose to do in the case or json consisting of scalars, or
arrays, or with nested elements?

cheers

andrew

--
Andrew Dunstan
EDB: https://www.enterprisedb.com

At the moment, this cast supports only these structures, as it was enough
for my tasks:
{str:numeric}
{str:str}
{str:bool}
{str:null}
But it's a great idea and I'll think about implementing it.

вт, 2 апр. 2024 г. в 19:48, Andrew Dunstan <andrew@dunslane.net>:

On 2024-04-02 Tu 11:43, ShadowGhost wrote:

At the moment, this cast supports only these structures, as it was
enough for my tasks:
{str:numeric}
{str:str}
{str:bool}
{str:null}
But it's a great idea and I'll think about implementing it.

Please don't top-post on the PostgreSQL lists. See
<https://wiki.postgresql.org/wiki/Mailing_Lists#Email_etiquette_mechanics&gt;

I don't think a cast that doesn't cater for all the forms json can take
is going to work very well. At the very least you would need to error
out in cases you didn't want to cover, and have tests for all of those
errors. But the above is only a tiny fraction of those. If the error
cases are going to be so much more than the cases that work it seems a
bit pointless.

cheers

andrew

--
Andrew Dunstan
EDB:https://www.enterprisedb.com

On 2024-04-03 Wn 04:21, Andrew Dunstan

I don't think a cast that doesn't cater for all the forms json can take is
going to work very well. At the very least you would need to error out in
cases you didn't want to cover, and have tests for all of those errors. But
the above is only a tiny fraction of those. If the error cases are going to
be so much more than the cases that work it seems a bit pointless.

Hi everyone
I changed my mail account to be officially displayed in the correspondence.
I also made an error conclusion if we are given an incorrect value. I
believe that such a cast is needed by PostgreSQL since we already have
several incomplete casts, but they perform their duties well and help in
the right situations.

cheers
Antoine Violin

Antoine

On Mon, Jul 15, 2024 at 12:42 PM Andrew Dunstan <andrew@dunslane.net> wrote:

On Mon, Jul 15, 2024 at 12:44 PM Антуан Виолин <violin.antuan@gmail.com>
wrote:

On 2024-04-03 Wn 04:21, Andrew Dunstan

I don't think a cast that doesn't cater for all the forms json can take
is going to work very well. At the very least you would need to error out
in cases you didn't want to cover, and have tests for all of those errors.
But the above is only a tiny fraction of those. If the error cases are
going to be so much more than the cases that work it seems a bit pointless.

Hi everyone
I changed my mail account to be officially displayed in the correspondence.
I also made an error conclusion if we are given an incorrect value. I
believe that such a cast is needed by PostgreSQL since we already have
several incomplete casts, but they perform their duties well and help in
the right situations.

cheers
Antoine Violin

Antoine

On Mon, Jul 15, 2024 at 12:42 PM Andrew Dunstan <andrew@dunslane.net>
wrote:

On 2024-04-02 Tu 11:43, ShadowGhost wrote:

At the moment, this cast supports only these structures, as it was enough
for my tasks:
{str:numeric}
{str:str}
{str:bool}
{str:null}
But it's a great idea and I'll think about implementing it.

Please don't top-post on the PostgreSQL lists. See
<https://wiki.postgresql.org/wiki/Mailing_Lists#Email_etiquette_mechanics&gt;
<https://wiki.postgresql.org/wiki/Mailing_Lists#Email_etiquette_mechanics&gt;

I don't think a cast that doesn't cater for all the forms json can take
is going to work very well. At the very least you would need to error out
in cases you didn't want to cover, and have tests for all of those errors.
But the above is only a tiny fraction of those. If the error cases are
going to be so much more than the cases that work it seems a bit pointless.

cheers

andrew

--
Andrew Dunstan
EDB: https://www.enterprisedb.com

Hi! I agree in some cases this cast can be useful.
I Have several comments about the patch:
1)I think we should call pfree on pairs(now we call palloc, but not pfree)
2)I think we should add error handling of load_external_function or maybe
rewrite using of DirectFunctionCall
3)i think we need replace all strdup occurences to pstrdup
4)why such a complex system , you first make global variables there to load
a link to functions there, and then wrap this pointer to a function through
a define?
5) postgres=# SELECT '{"aaa": "first_value", "aaa":
"second_value"}'::jsonb::hstore;
hstore
-----------------------
"aaa"=>"second_value"
(1 row)
is it documented behaviour?