After a little controversy on the PostgreSQL Hackers mailing list, I got the idea loud and clear that some users weren't happy with the new jsonb features, and in particular the fact that they weren't getting a way to add values to structures nested well inside the jsonb object. Eventually I came up with the idea that we should do this via an enhanced jsonb_replace function. This function gained an additional boolean parameter, defaulting to true, and when it is true the function will not only replace existing items but if the last element of the path designates an object key or array element that is not present, it will be created with the new value. Since this is no longer just replacement of existing values, the function has been renamed jsonb_set. These changes are based in some original code from Dmitry Dolgov, heavily modified by be, and they have just been committed for inclusion in release 9.5. Here are a few examples:
andrew=# select jsonb_set('[]','{0}','"a value"');
jsonb_set
-------------
["a value"]
andrew=# select jsonb_set('{}','{x}','"a value"',false);
jsonb_set
-----------
{}
andrew=# select jsonb_set('{"f1":{"f2":{"y":1}}}','{f1,f2,x}','"a value"');
jsonb_set
------------------------------------------
{"f1": {"f2": {"x": "a value", "y": 1}}}
Although this is actually a fairly small change, in terms of code, its impact could be quite big. I believe it will add significantly to our compelling JSON story.