Re: [HACKERS] [PATCH] Generic type subscripting

čt 14. 1. 2021 v 18:09 odesílatel Dian M Fay <dian(dot)m(dot)fay(at)gmail(dot)com> napsal:

> On Thu Jan 14, 2021 at 10:04 AM EST, Dmitry Dolgov wrote:
> > > On Tue, Jan 12, 2021 at 08:02:59PM +0100, Pavel Stehule wrote:
> > > ne 10. 1. 2021 v 19:52 odesílatel Pavel Stehule <
> pavel(dot)stehule(at)gmail(dot)com>
> > > napsal:
> > >
> > > I tested behaviour and I didn't find anything other than the mentioned
> > > issue.
> > >
> > > Now I can check this feature from plpgsql, and it is working. Because
> there
> > > is no special support in plpgsql runtime, the update of jsonb is
> > > significantly slower than in update of arrays, and looks so update of
> jsonb
> > > has O(N2) cost. I don't think it is important at this moment - more
> > > important is fact, so I didn't find any memory problems.
> >
> > Thanks for testing. Regarding updates when the structure doesn't match
> > provided path as I've mentioned I don't have strong preferences, but on
> > the second though probably more inclined for returning an error in this
> > case. Since there are pros and cons for both suggestions, it could be
> > decided by vote majority between no update (Dian) or an error (Pavel,
> > me) options. Any +1 to one of the options from others?
> >
> > Other than that, since I've already posted the patch for returning an
> > error option, it seems that the only thing left is to decide with which
> > version to go.
>
> The trigger issue (which I did verify) makes the "no update" option
> unworkable imo, JavaScript's behavior notwithstanding. But it should be
> called out very clearly in the documentation, since it does depart from
> what people more familiar with that behavior may expect. Here's a quick
> draft, based on your v44 patch:
>
> <para>
> <type>jsonb</type> data type supports array-style subscripting expressions
> to extract or update particular elements. It's possible to use multiple
> subscripting expressions to extract nested values. In this case, a chain
> of
> subscripting expressions follows the same rules as the
> <literal>path</literal> argument in <literal>jsonb_set</literal> function,
> e.g. in case of arrays it is a 0-based operation or that negative integers
> that appear in <literal>path</literal> count from the end of JSON arrays.
> The result of subscripting expressions is always of the jsonb data type.
> </para>
> <para>
> <command>UPDATE</command> statements may use subscripting in the
> <literal>SET</literal> clause to modify <type>jsonb</type> values. Every
> affected value must conform to the path defined by the subscript(s). If
> the
> path cannot be followed to its end for any individual value (e.g.
> <literal>val['a']['b']['c']</literal> where <literal>val['a']</literal> or
> <literal>val['b']</literal> is null, a string, or a number), an error is
> raised even if other values do conform.
> </para>
> <para>
> An example of subscripting syntax:
>

+1

Pavel