How do you create a Postgresql JSONB array in array index?

Question

I have structure like this: user_id, a.

a is of type jsonb and has the following structure:

{ b: 
   [
     {ids: [1,2,3,4]}, 
     {ids: [2,3,4]}, 
     {ids: [1,2,4]}, 
     ...
   ]
}

How would I make an index that enabled me to find all users (user_id) that has a certain id in the ids list?

Answer 1

Is a GIN index what you want?

It seems that you first need to organized the IDs into a form that is more tractable. I'm more familiar with Python than I am with the PostgreSQL ways of manipulating JSON, so I used PL/Python for this purpose.

   DROP TABLE IF EXISTS ids;

CREATE TABLE ids (user_id integer, a jsonb);

INSERT INTO ids VALUES 
    (1, '{"b": [{"ids": [1, 2, 3, 4]}, {"ids": [2, 3, 4]}, {"ids": [1, 2, 4]}]}'),
    (2, '{"b": [{"ids": [2, 3, 4]}]}'),
    (3, '{"b": [{"ids": [4, 5, 6]}, {"ids": [6, 7, 8]}]}');

CREATE OR REPLACE FUNCTION extract_ids(a_json jsonb) 
RETURNS int[] AS
$BODY$
    import json
    s = set()
    a = json.loads(a_json)
    for key in a.keys():
        for id_set in a[key]:
            s.update(id_set['ids'])
    return(list(s))
$BODY$ LANGUAGE plpythonu IMMUTABLE;

SELECT user_id, extract_ids(a)
FROM ids;

CREATE INDEX ON ids USING gin (extract_ids(a));

SELECT user_id 
FROM ids
WHERE ARRAY[3] <@ extract_ids(a);