使用 SQL 删除 postgres 中 jsonb 列中的长键值对

Question

I am using a materialized view to merge an query 3 json columns because I want to query all of them together with 1 GIN index. The view looks similar to this:

CREATE MATERIALIZED VIEW IF NOT EXISTS test_materialized_view AS
SELECT t1.id, (t1.data1 || t1.data2 || COALESCE(t2.data1, '{}'::jsonb)) "data"
FROM table_1 t1 LEFT JOIN table_2 t2 ON (...);

Now it can happen that there are longer key value pairs in the json data which I never want to query and which can be stored 1000 of times because they are in t2.data1. Is it possible to filter the merged json and only include key value pairs with a length less than x characters? Does this even make a difference / reduce saved data?

I dont know the json keys of these fields. I basically just want to remove all key value pairs which are longer than x characters or array / nested objects but did not really find a good way to do this in postgres

Answer 1

There is no built-in function for this. You will need to write your own.

Something along the lines:

create function remove_long_values(p_input jsonb, p_maxlen int)
  returns jsonb
as
$$
  select coalesce(jsonb_object_agg(e.ky, e.val), '{}')
  from jsonb_each(p_input) as e(ky,val) 
  where length(e.val::text) <= p_maxlen;
$$
language sql
immutable
parallel safe;

The above does not deal with nested key/value pairs. It only checks this on the first level.

Then use it in the query:

CREATE MATERIALIZED VIEW IF NOT EXISTS test_materialized_view 
AS
SELECT t1.id, t1.data1 || t1.data2 || remove_long_values(t2.data1,250) as "data"
FROM table_1 t1 
  LEFT JOIN table_2 t2 ON (...);