Extracting very long string from JSON to CLOB - json

Question

I'm trying to extract a very long string into clob from json_object_t and got some weird database behaviour (12.2c) with json_object_t.get_clob(key) method.
There is a sample code than does following:
DECLARE
l_data CLOB := '{"text": "very long string about 1M chars"}';
l_json json_object_t;
l_text CLOB := EMPTY_CLOB();
BEGIN
l_json := json_object_t.parse(l_data);
l_text := l_json.get_clob('text');
dbms_output.put_line('got ' || dbms_lob.getlength(l_text) || ' chars');
END;
When string length in a 'text' key is less than 32k chars, get_clob method works just fine and shows appropriate result, but with longer strings it produces an empty clob with zero length, just like get_string, but without 'character string buffer too small' exception.
I've tried to get same data via json_table query, but it cannot extract data to clob column at all, only varchar/number is allowed.
Is that a bug or am I doing something wrong? Is there any other ways to extract long strings from JSON keys?

Answer 1

I work with Oracle Database JSON Store group and would be happy to assist you with this issue you're facing. Could you try the alternate get_Clob procedure instead of this function and tell us what the behavior is?
Signature:
MEMBER PROCEDURE get_Clob(key VARCHAR2, c IN OUT CLOB)
Please try this:
DECLARE
content_json CLOB := '{"value":"';
content_json_end CLOB := '"}';
content_tmp CLOB := 'ab';
l_json json_object_t;
l_text CLOB := EMPTY_CLOB();
tmp clob;
BEGIN
-- 13 gives 16K
-- 14 gives 32K
FOR count IN 1 .. 14
loop
dbms_lob.append(content_tmp, content_tmp); -- a bad append for now
END loop;
dbms_lob.append(content_json, content_tmp);
dbms_lob.append(content_json, content_json_end);
l_json := json_object_t.parse(content_json);
l_json.get_clob('value', l_text); -- !!! TRY THIS PROC get_Clob
--l_text := l_json.get_clob('value');
dbms_output.put_line('Lob size in Kb: ');
dbms_output.put_line(dbms_lob.getLength(l_text) / 1024);
END;
/
Looking forward to your findings..

Answer 2

This works as well. Instead using the the get_clob method, use c:
DECLARE
CURSOR crsrJSON IS
SELECT
json_object( 'employee_id' VALUE employee_id,
'first_name' VALUE first_name,
'last_name' VALUE last_name,
'email' VALUE email,
'phone_number' VALUE phone_number,
'hire_date' VALUE to_char(hire_date,'MM/DD/YYYY'),
'job_id' VALUE job_id,
'salary' VALUE nvl(salary,0),
'commission_pct' VALUE nvl(commission_pct,0),
'manager_id' VALUE NVL(manager_id,0),
'department_id' VALUE NVL(department_id,0),
'department_name' VALUE (select department_name from departments x where x.department_id = hr.department_id),
'job_title' VALUE (select job_title from jobs x where x.job_id = hr.job_id)) emp_data
FROM
employees hr;
js_array JSON_ARRAY_T := new JSON_ARRAY_T;
json_obj JSON_OBJECT_T := JSON_OBJECT_T();
json_clob CLOB := EMPTY_CLOB();
BEGIN
FOR data_rec IN crsrJSON LOOP
js_array.append(JSON_ELEMENT_T.parse(data_rec.emp_data));
END LOOP;
json_obj.put('data',js_array);
IF json_obj.has('data') THEN
json_clob := json_obj.to_clob;
DBMS_OUTPUT.PUT_LINE(json_clob);
ELSE
DBMS_OUTPUT.PUT_LINE('Nope');
END IF;
END;

Answer 3

with data as
( select
xmlelement(e,regexp_replace('{"name":"'||colname||'"}', '[[:cntrl:]]', ''),',') col1
from tblname
)
select
rtrim(replace(replace(replace(xmlagg(col1).getclobval(),'&'||'quot;','"'),'<E>',''),'</E>',''),',')
as very_long_json
from data;