Update or create nested jsonb value using single update command

Question

Let us say I have [in Postgres 9.6] a JSONB column named xyz. In an update, I want to set the .foo.bar key of this column to {\"

Answer 1

You can just use || to concatenate. It will overwrite or add any json value.

SELECT '{}'::jsonb || '{"foo":"bar"}'::jsonb
UPDATE tablename SET jdoc = jdoc || '{"foo":"bar"}'::jsonb

It's that easy. I rarely use the functions in my software.

In the case of merging:

create or replace function jsonb_merge(orig jsonb, delta jsonb)
returns jsonb language sql as $$
    select
        jsonb_object_agg(
            coalesce(keyOrig, keyDelta),
            case
                when valOrig isnull then valDelta
                when valDelta isnull then valOrig
                when (jsonb_typeof(valOrig) <> 'object' or jsonb_typeof(valDelta) <> 'object') then valDelta
                else jsonb_merge(valOrig, valDelta)
            end
        )
    from jsonb_each(orig) e1(keyOrig, valOrig)
    full join jsonb_each(delta) e2(keyDelta, valDelta) on keyOrig = keyDelta
$$;