Force uniqueness in JSONB array - arrays

Question

Let's say I have a table students with a column type jsonb where I store a list with students' additional emails. A student row looks like this
student_id
name
emails
1
John Doe
[j.doe#email.com]
I'm using the following query to update the emails column:
UPDATE students SET emails = emails || '["j.doe#email.com"]'::jsonb
WHERE student_id=1
AND NOT emails #> '["j.doe#email.com"]'::jsonb;
Once the column emails is filled, if I reuse query above with the parameter ["j.doe#email.com", "john#email.com"], the column emails would be update with repeated value:
student_id
name
emails
1
Student 1
[j.doe#email.com, j.doe#email.com, john#email.com]
Is there a way to make sure that in the column emails I'll always have a jsonb list with only unique values ?

Answer 1

Use this handy function which removes duplicates from a jsonb array:
create or replace function jsonb_unique_array(jsonb)
returns jsonb language sql immutable as $$
select jsonb_agg(distinct value)
from jsonb_array_elements($1)
$$;
Your update statement may look like this:
update students
set emails = jsonb_unique_array(emails || '["j.doe#email.com", "john#email.com"]'::jsonb)
where student_id=1
and not emails #> '["j.doe#email.com", "john#email.com"]'::jsonb
Test it in db<>fiddle.