Add array at specific index/position in jsonb Postgresql field - arrays

Question

I'm wondering if there's a way to append array to a specific index/position in an jsonb array in Postgresql 9.6?
Let's imagine that my code below is my json:
{
"date": "2018-02-12",
"author": "devoplex",
"block": [
{ "color": "#C70039", "title": "Fruit" },
{ "color": "#DAF7A6", "title": "Vegetable" },
{ "color": "#DAF7A6", "title": "Meat" }
]
}
I want to append this object in my "block" array:
{ "color": "#581845", "title": "Candy" }
But I want this object to become the third index/position without replacing anything. So finally I can have this result:
{
"date": "2018-02-12",
"author": "devoplex",
"block": [
{ "color": "#C70039", "title": "Fruit" }, <---- Initial line
{ "color": "#DAF7A6", "title": "Vegetable" }, <---- Initial line
{ "color": "#581845", "title": "Candy" }, <---- New line
{ "color": "#DAF7A6", "title": "Meat" } <---- Initial line
]
}
This example in not my actual code but it's the same issue. This is for the construction of a form, so it need to be in a specific order or else it won't make any sense. Thanks you.

Answer 1

an ugly wheel, but nothing smarter comes fast:
with c(jb) as (values('{
"date": "2018-02-12",
"author": "devoplex",
"block": [
{ "color": "#C70039", "title": "Fruit" },
{ "color": "#DAF7A6", "title": "Vegetable" },
{ "color": "#DAF7A6", "title": "Meat" }
]
}'::jsonb))
, m as (select jb,e,case when o <3 then o else o+1 end o from c, jsonb_array_elements(jb->'block') with ordinality t(e,o) union all select jb, '{ "color": "#581845", "title": "Candy" }',3 from c)
, n as (select distinct jb,jsonb_agg(e) over (order by o) a from m)
select jsonb_pretty(jsonb_set(jb,'{block}',a)) from n order by length(a::text) desc limit 1;
jsonb_pretty
----------------------------------
{ +
"date": "2018-02-12", +
"block": [ +
{ +
"color": "#C70039", +
"title": "Fruit" +
}, +
{ +
"color": "#DAF7A6", +
"title": "Vegetable"+
}, +
{ +
"color": "#581845", +
"title": "Candy" +
}, +
{ +
"color": "#DAF7A6", +
"title": "Meat" +
} +
], +
"author": "devoplex" +
}
of course you should replace 3 with other digit if you want it in other index... http://dbfiddle.uk/?rdbms=postgres_10&fiddle=ccef24ef615b30eec07be9d1be5a1f8d here's example with index taken out of main query to ind CTE