Postgresql: Find row via text in json array of objects - sql

Question

I am trying to find rows in my Postgresql Database where a json column contains a given text.
row schema:
id | name | subitems
-----------------------------------------------------------------
1 | "item 1" | [{name: 'Subitem A'}, {name: 'Subitem B'}]
2 | "item 2" | [{name: 'Subitem C'}, {name: 'Subitem D'}]
My wanted result for query 'Subitem B'
id | name | subitems
-----------------------------------------------------------------
1 | "item 1" | [{name: 'Subitem A'}, {name: 'Subitem B'}]
I can search for the first subitem like this:
WHERE lower(subitems->0->>\'name\') LIKE '%subitem a%'
But obviously I can't find any other subitem but the first one this way.
I can get all the names of my subitems:
SELECT lower(json_array_elements(subitems)->>'name') FROM ...
But it gives me 2 rows containing the names:
lower
----------------------------------------------------------------
"subitem a"
"subitem b"
What I actually need is 1 row containing the item.
Can anyone tell me how to do that?

Answer 1

You're almost there. Your query:
SELECT lower(json_array_elements(subitems)->>'name') FROM foo;
That gets you what you want to filter against. If you plop that into a subquery, you get the results you're looking for:
# SELECT *
FROM foo f1
WHERE 'subitem a' IN
(SELECT lower(json_array_elements(subitems)->>'name')
FROM foo f2 WHERE f1.id = f2.id
);
id | name | subitems
----+--------+------------------------------------------------
1 | item 1 | [{"name": "Subitem A"}, {"name": "Subitem B"}]
(1 row)
Edited to add
Okay, to support LIKE-style matching, you'll have to go a bit deeper, putting a subquery into your subquery. Since that's a bit hard to read, I'm switching to using common table expressions.
WITH all_subitems AS (
SELECT id, json_array_elements(subitems)->>'name' AS subitem
FROM foo),
matching_items AS (
SELECT id
FROM all_subitems
WHERE
lower(subitem) LIKE '%subitem a%')
SELECT *
FROM foo
WHERE
id IN (SELECT id from matching_items);
That should get you what you need. Note that I moved the call to lower up a level, so it's alongside the LIKE. That means the filtering condition is in one spot, so you can switch to a regular expression match, or whatever, more easily.