Expand Postgresql Nested Array Json Field - json

Question

I have a table (log_table) and in this table there is a nested array json field (activities). With using this activities field, I want to normalize my row.
log_table:
- id:long
- activities:json
- date:timestamp
example activities field:
[
{
"actionType":"NOTIFICATION",
"items":null
},
{
"actionType":"MUTATION",
"items":[
{
"id":387015007,
"name":"epic",
"value":{
"currency":"USD",
"amount":1.76
}
},
{
"id":386521039,
"name":"test",
"value":{
"currency":"USD",
"amount":1.76
}
}
]
}
]
As query, I've tried:
select
*
from
log_table l,
json_array_elements(l.activities) elems,
json_array_elements(elems->'items') obj;
With this query, I got error like below:
ERROR: cannot call json_array_elements on a scalar
Is there any suggestion?

Answer 1

The lack of items should be marked as [null], not null. You can use the case expression to correct this, e.g.:
select elems->>'actionType' as action_type, obj
from log_table
cross join jsonb_array_elements(l.activities::jsonb) elems
cross join jsonb_array_elements(case elems->'items' when 'null' then '[null]' else elems->'items' end) obj
action_type | obj
--------------+---------------------------------------------------------------------------------
NOTIFICATION | null
MUTATION | {"id": 387015007, "name": "epic", "value": {"amount": 1.76, "currency": "USD"}}
MUTATION | {"id": 386521039, "name": "test", "value": {"amount": 1.76, "currency": "USD"}}
(3 rows)