Merging JSONB values in PostgreSQL? - json

Question

Using the || operator yields the following result:
select '{"a":{"b":2}}'::jsonb || '{"a":{"c":3}}'::jsonb ;
?column?
-----------------
{"a": {"c": 3}}
(1 row)
I would like to be able to do achieve the following result (?? just a placeholder for the operator):
select '{"a":{"b":2}}'::jsonb ?? '{"a":{"c":3}}'::jsonb ;
?column?
-----------------
{"a": {"b": 2, "c": 3}}
(1 row)
So, you can see the top-level a key has its child values "merged" such that the result contains both b and c.
How do you "deep" merge two JSONB values in Postgres?
Is this possible, if so how?
A more complex test case:
select '{"a":{"b":{"c":3},"z":true}}'::jsonb ?? '{"a":{"b":{"d":4},"z":false}}'::jsonb ;
?column?
-----------------
{"a": {"b": {"c": 3, "d": 4}, "z": false}}
(1 row)
Another test case where a primitive "merges over" and object:
select '{"a":{"b":{"c":3},"z":true}}'::jsonb ?? '{"a":{"b":false,"z":false}}'::jsonb ;
?column?
-----------------
{"a": {"b": false, "z": false}}
(1 row)

Answer 1

You should merge unnested elements using jsonb_each() for both values. Doing this in a non-trivial query may be uncomfortable, so I would prefer a custom function like this one:
create or replace function jsonb_my_merge(a jsonb, b jsonb)
returns jsonb language sql as $$
select
jsonb_object_agg(
coalesce(ka, kb),
case
when va isnull then vb
when vb isnull then va
else va || vb
end
)
from jsonb_each(a) e1(ka, va)
full join jsonb_each(b) e2(kb, vb) on ka = kb
$$;
Use:
select jsonb_my_merge(
'{"a":{"b":2}, "d": {"e": 10}, "x": 1}'::jsonb,
'{"a":{"c":3}, "d": {"f": 11}, "y": 2}'::jsonb
)
jsonb_my_merge
------------------------------------------------------------------
{"a": {"b": 2, "c": 3}, "d": {"e": 10, "f": 11}, "x": 1, "y": 2}
(1 row)
You can slightly modify the function using recursion to get a solution working on any level of nesting:
create or replace function jsonb_recursive_merge(a jsonb, b jsonb)
returns jsonb language sql as $$
select
jsonb_object_agg(
coalesce(ka, kb),
case
when va isnull then vb
when vb isnull then va
when jsonb_typeof(va) <> 'object' then va || vb
else jsonb_recursive_merge(va, vb)
end
)
from jsonb_each(a) e1(ka, va)
full join jsonb_each(b) e2(kb, vb) on ka = kb
$$;
Examples:
select jsonb_recursive_merge(
'{"a":{"b":{"c":3},"x":5}}'::jsonb,
'{"a":{"b":{"d":4},"y":6}}'::jsonb);
jsonb_recursive_merge
------------------------------------------------
{"a": {"b": {"c": 3, "d": 4}, "x": 5, "y": 6}}
(1 row)
select jsonb_recursive_merge(
'{"a":{"b":{"c":{"d":{"e":1}}}}}'::jsonb,
'{"a":{"b":{"c":{"d":{"f":2}}}}}'::jsonb)
jsonb_recursive_merge
----------------------------------------------
{"a": {"b": {"c": {"d": {"e": 1, "f": 2}}}}}
(1 row)
Finally, the variant of the function with changes proposed by OP (see comments below):
create or replace function jsonb_recursive_merge(a jsonb, b jsonb)
returns jsonb language sql as $$
select
jsonb_object_agg(
coalesce(ka, kb),
case
when va isnull then vb
when vb isnull then va
when jsonb_typeof(va) <> 'object' or jsonb_typeof(vb) <> 'object' then vb
else jsonb_recursive_merge(va, vb) end
)
from jsonb_each(a) e1(ka, va)
full join jsonb_each(b) e2(kb, vb) on ka = kb
$$;

Answer 2

This kind of "deep merge" can be interpreted quite differently, depending on your use case. For completeness, my intuition usually dictates the following rules:
object + object: Every property survives from each object, which is not in the other object (JSON's null value is considered to be in the object, if it's explicitly mentioned). When a property is in both objects, the merge continues recursively with the same rules (this point is usually agreed on).
array + array: The result is the concatenation of the two arrays.
array + primitive/object: the result is the first array, with the second JSON value appended to it.
any other cases: The result is the second JSON value (so f.ex. primitives or incompatible types override each other).
create or replace function jsonb_merge_deep(jsonb, jsonb)
returns jsonb
language sql
immutable
as $func$
select case jsonb_typeof($1)
when 'object' then case jsonb_typeof($2)
when 'object' then (
select jsonb_object_agg(k, case
when e2.v is null then e1.v
when e1.v is null then e2.v
else jsonb_merge_deep(e1.v, e2.v)
end)
from jsonb_each($1) e1(k, v)
full join jsonb_each($2) e2(k, v) using (k)
)
else $2
end
when 'array' then $1 || $2
else $2
end
$func$;
This function's added bonus is that it can be called with literally any type of JSON values: always produces a result & never complains about JSON value types.
http://rextester.com/FAC95623

Answer 3

After PostgreSQL 9.5 you can use jsonb_set function:
'{a,c}' looking into path if it is not there, it will created.
'{"a":{"c":3}}'::jsonb#>'{a,c}' this will get the value of c
new_value added if create_missing is true ( default is true)
Hier is document jsonb -functions
select jsonb_set('{"a":{"b":2}}', '{a,c}','{"a":{"c":3}}'::jsonb#>'{a,c}' )
Result: {"a":{"c":3,"b":2}}
Merge more attribute at once:
with jsonb_paths(main_part,missing_part) as (
values ('{"a":{"b":2}}','{"a":{"c":3,"d":4}}')
)
select jsonb_object_agg(t.k,t.v||t2.v)
from jsonb_paths,
jsonb_each(main_part::jsonb) t(k,v),
jsonb_each(missing_part::jsonb) t2(k,v);
result: {"a":{"c":3,"b":2,"d":4}}

Answer 4

As #lightSouls say, after PostgreSQL 9.5 you can use jsonb_set() function... But you must to learn how to use it!
jsonb_set can merge or destroy...
Supposing j:='{"a":{"x":1},"b":2}'::jsonb.
jsonb_set(j, '{a,y}', '1'::jsonb); will merge object {"y":1} with object {"x":1}. Result: {"a": {"x": 1, "y": 1}, "b": 2}
jsonb_set(j, '{a}', '{"x":1}'::jsonb); will destroy! replacing full old object by the new one.Result: {"a": {"x": 1}, "b": 2}

Answer 5

Combining (merging :-D) answers from #klin, #pozs and comment from #Arman Khubezhov while also actually merging arrays instead of concatenating (which resulted in duplicates otherwise), came up with the following function:
create or replace function jsonb_merge_deep(jsonb, jsonb)
returns jsonb
language sql
immutable
as $func$
select case jsonb_typeof($1)
when 'object' then
case jsonb_typeof($2)
when 'object' then (
select jsonb_object_agg(k,
case
when e2.v is null then e1.v
when e1.v is null then e2.v
else jsonb_merge_deep(e1.v, e2.v)
end
)
from jsonb_each($1) e1(k, v)
full join jsonb_each($2) e2(k, v) using (k)
)
else COALESCE($2, $1)
end
when 'array' then
(
SELECT jsonb_agg(items.val)
FROM (
SELECT jsonb_array_elements($1) AS val
UNION
SELECT jsonb_array_elements($2) AS val
) AS items
)
else $2
end
$func$;
Based on comment from #Arman Khubezhov, enhanced the case when any of $1 or $2 is null with:
else COALESCE($2, $1)
And added real merge (no duplicate) of the 2 arrays values with:
when 'array' then
(
SELECT jsonb_agg(items.val)
FROM (
SELECT jsonb_array_elements($1) AS val
UNION
SELECT jsonb_array_elements($2) AS val
) AS items
)
Glad if one can come up with a enhanced code for this one - like an existing PostreSQL function I am not aware of?
Pros: no data loss when combining 2 JSONB values or updating a JSONB field in an UPDATE query like.
UPDATE my_table
SET my_jsonb_field = jsonb_merge_deep(my_jsonb_field, '{ "a": { "aa" : { "aaa" : [6, 4, 7] } } }'::jsonb)
Cons: removing a key/value or array value requires a dedicated query.