how to merge two json_arrays in postgresql - json

Question

I need to MERGE two JSONB_ARRAYS
i have in my table column jsonb of items which looks like this:
[
{"fav": 1, "is_active": true, "date": "1999-00-00 11:07:05.710000"},
{"fav": 2, "is_active": true, "date": "1998-00-00 11:07:05.710000"}
]
where fav's value is unique number.
And i have incoming data, where could be the same items which also exists in my table and also new items and after merging the result must be that way where new items just need to add but existing items i need to update
so after merging the result must look like this:
merge:
[
{"fav": 1, "is_active": true, "date": "1999-00-00 11:07:05.710000"},
{"fav": 2, "is_active": true, "date": "1998-00-00 11:07:05.710000"}
]::jsonb ||
[
{"fav": 3, "is_active": true, "date": "2019-00-00 11:07:05.710000"},
{"fav": 1, "is_active": false, "date": "2020-00-00 11:07:05.710000"}
]::jsonb
------------------------------------------------------------------------
result:
[
{"fav": 1, "is_active": false, "date": "2020-00-00 11:07:05.710000"},
{"fav": 2, "is_active": true, "date": "1998-00-00 11:07:05.710000"},
{"fav": 3, "is_active": true, "date": "2019-00-00 11:07:05.710000"}
]
as expected the "fav": 1 -> was updated and "fav": 3 -> was added
maybe i need some refactroring structure of my json maybe something else?
and maybe it would be better if i retrieve json to Collection and work with objects and after all manipulations just save it back?
Update 1
i try write custom function:
CREATE OR REPLACE FUNCTION public.json_array_merge(data1 jsonb, merge_data jsonb)
RETURNS jsonb
IMMUTABLE
LANGUAGE sql
AS $$
SELECT jsonb_agg(expression)::jsonb
FROM (
WITH to_merge AS (
SELECT * FROM jsonb_each(jsonb_array_elements(merge_data))
)
SELECT *
FROM json_each(jsonb_array_elements(data1))
WHERE value NOT IN (SELECT value FROM to_merge)
UNION ALL
SELECT * FROM to_merge
) expression;
$$;
but now it doesnt work (

Answer 1

You probably will want to write a custom function to handle this. The default behaviour is to append each value because it has no way of knowing that you want fav to be unique.
If your data used fav as a key e.g.
{
"fav1": {"date": "2020-00-00 11:07:05.710000", "is_active": false},
"fav2": {"date": "1998-00-00 11:07:05.710000", "is_active": true},
"fav3": {"date": "2019-00-00 11:07:05.710000", "is_active": true}
}
this would be simple to manage, but since you are using an array you would need to make a custom function that iterates and check each value.
Edit you would need to run a few loops with plpgsql, this could be achieved more efficiently using plv8
CREATE OR REPLACE FUNCTION public.json_array_merge(
data_new jsonb,
data_old jsonb,
key_val text
)
RETURNS jsonb
AS $$
DECLARE
ret jsonb := '[]'::jsonb;
cur text;
add boolean := true;
i integer := 0;
ic integer := jsonb_array_length(data_old);
j integer := 0;
jc integer := jsonb_array_length(data_new);
BEGIN
IF ic > 0 AND jc > 0 THEN
-- populate or replace the records that are already there
WHILE i < ic LOOP
cur := null;
j := 0;
-- loop new array
WHILE j < jc LOOP
IF data_old->i->>key_val = data_new->j->>key_val THEN
cur := data_new->>j;
add := false;
END IF;
j := j + 1;
END LOOP;
-- add or replace
IF add THEN
ret := ret || format('[%s]', data_old->>i)::jsonb;
ELSE
ret := ret || format('[%s]', cur)::jsonb;
END IF;
add := true;
i := i + 1;
END LOOP;
-- loop through the new data again and add any values not in ret
ic := jsonb_array_length(ret);
j := 0;
WHILE j < jc LOOP
i := 0;
add := true;
WHILE i < ic LOOP
IF ret->i->>key_val = data_new->j->>key_val THEN
add := false;
END IF;
i := i + 1;
END LOOP;
IF add THEN
ret := ret || format('[%s]', data_new->>j)::jsonb;
END IF;
j := j + 1;
END LOOP;
ELSE
ret := data_new;
END IF;
RETURN ret;
END
$$
LANGUAGE plpgsql IMMUTABLE;
Running this should give you the desired result
SELECT json_array_merge(
'[{"fav": 3, "is_active": true, "date": "2019-00-00 11:07:05.710000"},{"fav": 1, "is_active": false, "date": "2020-00-00 11:07:05.710000"}]',
'[{"fav": 1, "is_active": true, "date": "1999-00-00 11:07:05.710000"},{"fav": 2, "is_active": true, "date": "1998-00-00 11:07:05.710000"}]',
'fav'
)