How can I insert into a Postgresql JSON array - json

Question

The table definition is:
chat_id serial primary key, last_update timestamp, messages JSON[]
and I want to insert a record like this:
insert into chats (messages) values ('{{"sender":"pablo","body":"they are on to us"}}');
with error:
ERROR: malformed array literal: "{{"sender":"pablo","body":"they are on to us"}}"
LINE 1: insert into chats (messages) values ('{{"sender":"pablo","bo...
I have also tried this approach :
insert into chats (messages) values (ARRAY('{"sender":"pablo","body":"they are on to us"}'));
Note that updating the row and inserting with array_append works OK.

Answer 1

I think this is a clash between the JSON notation that starts with { and the short hand array notation in Postgres where the string representation of an array is also denoted by an {.
The following works:
insert into chats
(messages)
values
(array['{"sender":"pablo","body":"they are on to us"}']::json[]);
This avoids the ambiguity of the {{ by using an explicit array constructor.
To make the array a json array you need to either cast the string to a json or the resulting array to a json[] (see the example above). Casting the whole array makes it easier if you have more than one JSON document in that row:
insert into chats
(messages)
values
(array['{"sender":"pablo","body":"they are on to us"}',
'{"sender":"arthur"}']::json[]);
alternatively:
insert into chats
(messages)
values
(array['{"sender":"pablo","body":"they are on to us"}'::json,
'{"sender":"arthur"}'::json]);

Answer 2

It is quite complicate to escape special characters. I would use insert from select to make it easier.
Create JSON array.
Convert it to set of JSON variables.
Convert the set to SQL array.
The select part below.
WITH bu AS (SELECT json_array_elements('[{"name":"obj1"},{"name":"obj2"},{"name":"obj3"},{"name":"obj4"}]'::json) AS bu)
SELECT array_agg(bu) FROM bu;