jsonb_concat: make sure we always return a non-scalar value

On 09/05/2015 02:47 AM, Oskari Saarenmaa wrote:

There was a long thread about concatenating jsonb objects to each
other, but that discussion didn't touch concatenating other types.
Currently jsonb_concat always just returns the other argument if one
of arguments is considered empty. This causes surprising behavior
when concatenating scalar values to empty arrays:

os=# select '[]'::jsonb || '1'::jsonb;
1

os=# select '[]'::jsonb || '[1]'::jsonb;
[1]

os=# select '[]'::jsonb || '1'::jsonb || '2'::jsonb;
[1, 2]

os=# select '0'::jsonb || '1'::jsonb;
[0, 1]

os=# select '{"x": "y"}'::jsonb || '[1]'::jsonb;
[{"x": "y"}, 1]

os=# select '{"x": "y"}'::jsonb || '1'::jsonb;
ERROR: invalid concatenation of jsonb objects

Attached a patch to fix and test this. Also added a test case for
concatenating two scalar values which currently produces an array..
I'm not sure that behavior makes sense, but didn't want to change that
in this patch as I guess someone could consider that feature useful.

This looks correct. Barring objection I'll apply this shortly.

cheers

andrew

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This looks correct. Barring objection I'll apply this shortly.

+1 Seems correct. Should we backpatch that?

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WWW: http://www.sigaev.ru/

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On 09/08/2015 10:48 AM, Teodor Sigaev wrote:

This looks correct. Barring objection I'll apply this shortly.

+1 Seems correct. Should we backpatch that?

Yes, certainly.

cheers

andrew

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On 8 September 2015 at 15:48, Teodor Sigaev <teodor@sigaev.ru> wrote:

This looks correct. Barring objection I'll apply this shortly.

+1 Seems correct. Should we backpatch that?

Yes, this needs correcting in 9.5 where it has been introduced.

Thom

On 09/08/2015 09:54 AM, Andrew Dunstan wrote:

On 09/05/2015 02:47 AM, Oskari Saarenmaa wrote:

There was a long thread about concatenating jsonb objects to each
other, but that discussion didn't touch concatenating other types.
Currently jsonb_concat always just returns the other argument if one
of arguments is considered empty. This causes surprising behavior
when concatenating scalar values to empty arrays:

os=# select '[]'::jsonb || '1'::jsonb;
1

os=# select '[]'::jsonb || '[1]'::jsonb;
[1]

os=# select '[]'::jsonb || '1'::jsonb || '2'::jsonb;
[1, 2]

os=# select '0'::jsonb || '1'::jsonb;
[0, 1]

os=# select '{"x": "y"}'::jsonb || '[1]'::jsonb;
[{"x": "y"}, 1]

os=# select '{"x": "y"}'::jsonb || '1'::jsonb;
ERROR: invalid concatenation of jsonb objects

Attached a patch to fix and test this. Also added a test case for
concatenating two scalar values which currently produces an array..
I'm not sure that behavior makes sense, but didn't want to change
that in this patch as I guess someone could consider that feature
useful.

This looks correct. Barring objection I'll apply this shortly.

Actually, I'm not sure the test is sufficient here. It looks to me like
we should only be taking this fast path if one operand is an empty array
and the other is a non-scalar array.

Otherwise we get things like this (second case is wrong, I think):

andrew=# select '[]'::jsonb || '"a"';
?column?
----------
["a"]

andrew=# select '[]'::jsonb || '{"a":"b"}';
?column?
------------
{"a": "b"}

andrew=# select '[1]'::jsonb || '{"a":"b"}';
?column?
-----------------
[1, {"a": "b"}]

cheers

andrew

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09.09.2015, 18:53, Andrew Dunstan kirjoitti:

On 09/08/2015 09:54 AM, Andrew Dunstan wrote:

On 09/05/2015 02:47 AM, Oskari Saarenmaa wrote:

There was a long thread about concatenating jsonb objects to each
other, but that discussion didn't touch concatenating other types.
Currently jsonb_concat always just returns the other argument if one
of arguments is considered empty. This causes surprising behavior
when concatenating scalar values to empty arrays:

os=# select '[]'::jsonb || '1'::jsonb;
1

os=# select '[]'::jsonb || '[1]'::jsonb;
[1]

os=# select '[]'::jsonb || '1'::jsonb || '2'::jsonb;
[1, 2]

os=# select '0'::jsonb || '1'::jsonb;
[0, 1]

os=# select '{"x": "y"}'::jsonb || '[1]'::jsonb;
[{"x": "y"}, 1]

os=# select '{"x": "y"}'::jsonb || '1'::jsonb;
ERROR: invalid concatenation of jsonb objects

Attached a patch to fix and test this. Also added a test case for
concatenating two scalar values which currently produces an array..
I'm not sure that behavior makes sense, but didn't want to change
that in this patch as I guess someone could consider that feature
useful.

This looks correct. Barring objection I'll apply this shortly.

Actually, I'm not sure the test is sufficient here. It looks to me like
we should only be taking this fast path if one operand is an empty array
and the other is a non-scalar array.

Otherwise we get things like this (second case is wrong, I think):

andrew=# select '[]'::jsonb || '"a"';
?column?
----------
["a"]

andrew=# select '[]'::jsonb || '{"a":"b"}';
?column?
------------
{"a": "b"}

andrew=# select '[1]'::jsonb || '{"a":"b"}';
?column?
-----------------
[1, {"a": "b"}]

It looks wrong, but I'm not sure what's right in that case. I think
it'd make sense to just restrict concatenation to object || object,
array || array and array || scalar and document that. I doubt many
people expect their objects to turn into arrays if they accidentally
concatenate an array into it. Alternatively the behavior could depend
on the order of arguments for concatenation, array || anything -> array,
object || array -> error.

/ Oskari

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On 9/9/15 12:03 PM, Oskari Saarenmaa wrote:

andrew=# select '[1]'::jsonb || '{"a":"b"}';
?column?
-----------------
[1, {"a": "b"}]

It looks wrong, but I'm not sure what's right in that case. I think
it'd make sense to just restrict concatenation to object || object,
array || array and array || scalar and document that. I doubt many
people expect their objects to turn into arrays if they accidentally
concatenate an array into it. Alternatively the behavior could depend
on the order of arguments for concatenation, array || anything -> array,
object || array -> error.

That definitely doesn't sound like a good default.

It might be useful to have a concat function that would concatinate
anything into an array. But if we don't provide one by default users
could always create their own with json__typeof() and json_build_array().
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Experts in Analytics, Data Architecture and PostgreSQL
Data in Trouble? Get it in Treble! http://BlueTreble.com

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On 09/09/2015 01:03 PM, Oskari Saarenmaa wrote:

09.09.2015, 18:53, Andrew Dunstan kirjoitti:

On 09/08/2015 09:54 AM, Andrew Dunstan wrote:

On 09/05/2015 02:47 AM, Oskari Saarenmaa wrote:

There was a long thread about concatenating jsonb objects to each
other, but that discussion didn't touch concatenating other types.
Currently jsonb_concat always just returns the other argument if one
of arguments is considered empty. This causes surprising behavior
when concatenating scalar values to empty arrays:

os=# select '[]'::jsonb || '1'::jsonb;
1

os=# select '[]'::jsonb || '[1]'::jsonb;
[1]

os=# select '[]'::jsonb || '1'::jsonb || '2'::jsonb;
[1, 2]

os=# select '0'::jsonb || '1'::jsonb;
[0, 1]

os=# select '{"x": "y"}'::jsonb || '[1]'::jsonb;
[{"x": "y"}, 1]

os=# select '{"x": "y"}'::jsonb || '1'::jsonb;
ERROR: invalid concatenation of jsonb objects

Attached a patch to fix and test this. Also added a test case for
concatenating two scalar values which currently produces an array..
I'm not sure that behavior makes sense, but didn't want to change
that in this patch as I guess someone could consider that feature
useful.

This looks correct. Barring objection I'll apply this shortly.

Actually, I'm not sure the test is sufficient here. It looks to me like
we should only be taking this fast path if one operand is an empty array
and the other is a non-scalar array.

Otherwise we get things like this (second case is wrong, I think):

andrew=# select '[]'::jsonb || '"a"';
?column?
----------
["a"]

andrew=# select '[]'::jsonb || '{"a":"b"}';
?column?
------------
{"a": "b"}

andrew=# select '[1]'::jsonb || '{"a":"b"}';
?column?
-----------------
[1, {"a": "b"}]

It looks wrong, but I'm not sure what's right in that case. I think
it'd make sense to just restrict concatenation to object || object,
array || array and array || scalar and document that. I doubt many
people expect their objects to turn into arrays if they accidentally
concatenate an array into it. Alternatively the behavior could depend
on the order of arguments for concatenation, array || anything ->
array, object || array -> error.

I don't think I want to change the semantics in general at this stage. A
simple minimal fix to handle the case of the fastpath where one of other
operand is empty, making it entirely consistent with the case where it's
not empty, is attached.

cheers

andrew