Add data from many-to-many to selection data - sql

Question

I have 3 tables:
"tags"
id serial
name text
"questions"
id serial
content jsonb
"questions_tags" (many-to-many)
question_id integer
tag_id integer
I can select all data from questions:
SELECT * FROM questions;
I can select tags of specific question:
SELECT t.*
FROM tags t
JOIN questions_tags qt ON t.id = qt.tag_id
JOIN questions q ON qt.question_id = q.id
WHERE q.id = 157;
I need to select all questions and add to this selection tags for every question.
I'm using nodejs and node-postgres and I need to get something like:
[
{
id: 1,
content: { someProp: 'someValue' },
tags: [
{ id: 58, name: 'sometag58' },
{ id: 216, name: 'sometag216' }
]
},
...
]
How can I do this without ORM, only with the help of vanilla SQL?

Answer 1

I would let PostgreSQL handle it for me:
with tagjson as (
select q.id, q.content, jsonb_agg(to_jsonb(tags)) as tags
from questions q
left join questions_tags qt on qt.question_id = q.id
left join tags on tags.id = qt.tag_id
group by q.id, q.content
)
select jsonb_pretty(jsonb_agg(to_jsonb(tagjson))) as result
from tagjson;
Result:
[
{
"id": 1,
"tags": [
{
"id": 58,
"name": "sometag58"
},
{
"id": 216,
"name": "sometag216"
}
],
"content": "some question 1 content"
}
]
db<>fiddle here
EDIT TO ADD:
Based on a conversation in the comments, the final query should be modified to:
select * from tagjson;
Or the CTE could be promoted to be a stand-alone query.
This allowed the conventional node syntax while preserving the aggregated tags array under the tags key:
const questions: Question[] = result.rows;