Avoid undesired flattening of jsonb arrays?
The || operator for the jsonb type has a surprising behaviour.
Instead of appending the right operand "as is" to the left operand,
it has a magic behaviour if the right operand is an array,
in which case it will append the items of the array,
instead of appending the array itself as a single value.
Example:
SELECT '[10,20]'::jsonb || '30'::jsonb;
[10, 20, 30]
SELECT '[10,20]'::jsonb || '[30]'::jsonb;
[10, 20, 30]
Since [10, 20, [30]] is desired in our case, we must use jsonb_insert() to work-around the problem in a not very nice way:
SELECT jsonb_insert('[10,20]'::jsonb,'{-1}','[30]'::jsonb,TRUE);
[10, 20, [30]]
Suggestions welcome if there is a better way to solve this problem.
Best regards,
Joel
On Fri, Dec 18, 2020 at 8:24 AM Joel Jacobson <joel@compiler.org> wrote:
The || operator for the jsonb type has a surprising behaviour.
Instead of appending the right operand "as is" to the left operand,
it has a magic behaviour if the right operand is an array,
in which case it will append the items of the array,
instead of appending the array itself as a single value.
It's not magic, and it is documented clearly.
I'll agree that the description could discuss the case explicitly, and the
array||scalar case could be added to the examples.
Suggestions welcome if there is a better way to solve this problem.
As you are writing literals just put an array in the to-be-merged array.
select '["a","b"]'::jsonb || '[["c","d"]]'::jsonb
David J.
"David G. Johnston" <david.g.johnston@gmail.com> writes:
I'll agree that the description could discuss the case explicitly, and the
array||scalar case could be added to the examples.
Yeah, the documentation completely fails to explain what happens
when the inputs aren't two arrays or two objects. I'd kind of assumed
that that's an error, but it isn't. Some experimentation indicates
that the behavior in all cases except two objects is to convert any
non-array input to a one-element array, reducing the situation to the
two-array case.
regards, tom lane
The following nicer work-around was suggested to me by Andreas Karlsson:
- jsonb_insert(x.jsonb_array,'{-1}',next_item.item,TRUE)
+ x.jsonb_array || jsonb_build_array(next_item.item)Show quoted text
On Fri, Dec 18, 2020, at 17:20, Tom Lane wrote:
"David G. Johnston" <david.g.johnston@gmail.com> writes:
I'll agree that the description could discuss the case explicitly, and the
array||scalar case could be added to the examples.Yeah, the documentation completely fails to explain what happens
when the inputs aren't two arrays or two objects. I'd kind of assumed
that that's an error, but it isn't. Some experimentation indicates
that the behavior in all cases except two objects is to convert any
non-array input to a one-element array, reducing the situation to the
two-array case.regards, tom lane