Oracle 12c: Remove JSON object from JSON array - json

Question

Need to create a function which takes input of CLOB and I need to remove array matching the condition.
create or replace FUNCTION remove_config_node_by_key (
p_in_json IN CLOB,
p_in_key IN VARCHAR2
) RETURN CLOB IS
l_ja json_array_t;
l_po json_object_t;
l_key VARCHAR2(500);
BEGIN
l_ja := json_array_t.parse(p_in_json);
FOR idx IN 0.. l_ja.get_size - 1 LOOP
l_po := json_object_t(l_ja.get(idx));
l_key := l_po.get_string('key');
-- check if the key matches with input and then delete that node.
dbms_output.put('Key to remove in the JSON: ' || l_key);
IF l_key = p_in_key THEN
dbms_output.put('Key to remove in the JSON: ' || l_key);
l_ja.remove (idx);
-- dbms_output.new_line;
dbms_output.put('Key is removed in the JSON: ' || l_key);
END IF;
END LOOP;
RETURN l_ja.to_clob;
END;
When called with:
update COLD_DRINKS cd set cd.configuration = remove_config_node_by_key(cd.configuration, 'b')
where country='INDIA';
I get error:
Error report -
ORA-30625: method dispatch on NULL SELF argument is disallowed
ORA-06512: at "SYS.JSON_OBJECT_T", line 72
ORA-06512: at "PLATFORM_ADMIN_DATA.REMOVE_CONFIG_NODE_BY_KEY", line 11
input JSON:
[
{
"key": "a",
"value": "lemon soda"
},
{
"key": "b",
"value": "Coke"
},
{
"key": "c",
"value": "Pepsi"
}
]
Expected JSON after execution:
[
{
"key": "a",
"value": "lemon soda"
},
{
"key": "c",
"value": "Pepsi"
}
]
I think something is wrong about this l_ja.remove (idx); as this one causes the exception. Not able to remove the object at index.

Answer 1

In 18c at least it works with your sample data (with the trailing comma removed from the array), but it gets that error with a null configuration.
So you can either test for null in your function, or exclude nulls from your update, or fix your data so it doesn't have nulls.
The simplest thing to do is probably add a null check:
...
BEGIN
IF p_in_json IS NULL THEN
RETURN NULL;
END IF;
l_ja := json_array_t.parse(p_in_json);
...
fiddle

Answer 2

You can also remove it using json_transform:
create or replace function remove_config_node_by_key (
p_in_json IN CLOB,
p_in_key IN VARCHAR2
) RETURN CLOB IS
l_result CLOB ;
begin
execute immediate q'~select json_transform(
:p_in_json,
REMOVE '$[*]?(#.key == "~' || p_in_key || q'~")'
)
from dual~' into l_result using p_in_json
;
return l_result ;
end ;
/
(with all usual comments regarding possible SQL injection...)

Answer 3

The issue was resolved when I added REVERSE in for loop
before [ERROR]
FOR idx IN 0.. l_ja.get_size - 1
after [PASS]
FOR idx IN REVERSE 0.. l_ja.get_size - 1
Complete working function
CREATE OR REPLACE FUNCTION remove_config_node_by_key (
p_in_json IN CLOB,
p_in_key IN VARCHAR2
) RETURN CLOB IS
l_ja json_array_t := json_array_t ();
l_po json_object_t;
l_key VARCHAR2(500);
BEGIN
l_ja := json_array_t.parse(p_in_json);
FOR idx IN REVERSE 0.. l_ja.get_size - 1
LOOP
l_po := json_object_t(l_ja.get(idx));
l_key := l_po.get_string('key');
-- check if the key matches with input and then delete that node.
IF l_key = p_in_key THEN
dbms_output.put_line('Key to remove in the JSON: ' || l_key || ' at index : ' || idx);
l_ja.remove (idx);
dbms_output.put_line('Key is removed in the JSON: ' || l_key);
END IF;
END LOOP;
RETURN l_ja.to_clob;
END;
/