On 06/10/2015 04:02 PM, Peter Geoghegan wrote:
On Wed, Jun 10, 2015 at 11:48 AM, Andrew Dunstan <and...@dunslane.net> wrote:
Sorry for the delay on this. I've been mostly off the grid, having an all
too rare visit from Tom "Mr Enum" Dunstan, and I misunderstood what you were
suggesting,
Thank you for working with me to address this. I've been busy with
other things the past few days too.
Please submit a patch to adjust the treatment of negative integers in the
old functions to be consistent with their treatment in the new functions.
i.e. in the range [-n,-1] they should refer to the corresponding element
counting from the right.
I've almost finished that patch. I'm currently blocked on deciding
what to do about the old path-orientated operators (#> and #>> for
json and jsonb types). It's rather painful to support pushing down
negative subscripting there -- maybe we should just not do so for
those variants, especially given that they're already notationally
inconsistent with the other operators that I'll be updating. What do
you think?
Maybe I'll come up with a simpler way of making that work by taking a
fresh look at it, but haven't done that yet.
My current, draft approach to making subscripting work with the json
variants (not the jsonb variants) is to use a second get_worker() call
in the event of a negative subscript, while making the first such call
(the existing get_worker() call) establish the number of top-level
array elements. That isn't beautiful, and involves some amount of
redundant work, but it's probably better than messing with
get_worker() in a more invasive way. Besides, this second get_worker()
call only needs to happen in the event of a negative subscript, and
I'm only really updating this (that is, updating routines like
json_array_element()) to preserve consistency with jsonb. What do you
think of that idea?
Just took a quick look. My impression is that the jsonb case should be
fairly easy. If the index is negative, add JB_ROOT_COUNT(container) to
it and use that as the argument to getIthJsonbValueFromContainer().
I agree that the json case looks a bit nasty. Maybe a better approach
would be to provide a function that, given a JsonLexContext, returns the
number of array elements of the current array. In get_array_start we
could call that if the relevant path element is negative and adjust it
accordingly.
cheers
andrew
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