Tracking SQL functions in Hasura - postgresql

Question

Basically I'm trying to compare two JSONB rows and return a numeric value. But I wanna be able to query for it. I'm not sure whether I should use a custom SQL function, a calculated field, or a Postgres generated column, so I need a bit of advice.
I have a jsonb column for each user that keeps a few hundreds of keys/values as such:
USERS TABLE:
| username | user_jsonb_column |
|-----------------------------------------------------------|
| 'user1' | {"key1":"value1", "key2":"value2" ... } |
|--------------|--------------------------------------------|
| 'user2' | {"key2":"value2", "key3":"value3" ... } |
I am trying to calculate the similarity of the jsonb rows of 2 users with a very simple SQL query as such:
SELECT ROUND ((
SELECT COUNT(*) from (
SELECT jsonb_each(user_jsonb_column)
FROM users WHERE username = 'johndoe'
INTERSECT
SELECT jsonb_each(user_jsonb_column)
FROM users WHERE username = 'janedoe'
)::decimal AS SAME_PAIRS
/ --divide it by
SELECT COUNT(*) from (
SELECT jsonb_object_keys(user_jsonb_column)
FROM users WHERE username = 'johndoe'
INTERSECT
SELECT jsonb_object_keys(user_jsonb_column)
FROM users WHERE username = 'janedoe'
) as SAME_KEYS
) * 100) as similarity_percentage
This is working as intended and gives me the similarity result between 2 json objects as a percentage.
I am trying to turn this into a function so that I can query for the similarity percentage of 2 users as such:
query {
calculate_similarity_percentage(
args: {user1: "johndoe", user2: "janedoe"}
){
similarity_percentage_value
}
}
But I'm stuck at this point because I'm not sure whether I should think in terms of a trackable custom SQL function (which should return SETOF <TABLE> but I need a numeric value), a computed field (which can also return BASE type), or maybe a Postgres generated column in my situation.
I've been reading https://hasura.io/docs/1.0/graphql/core/schema/custom-functions.html and https://hasura.io/docs/1.0/graphql/core/schema/computed-fields.html but I couldn't quite figure out how to approach this, so any kind of help or comment would be appreciated.
Update: Yes, as Laurenz Albe pointed out, I am able to create a function like this:
CREATE OR REPLACE FUNCTION public.calculate_similarity_percentage(text, text)
RETURNS numeric
LANGUAGE sql
STABLE
AS $function$
SELECT ROUND(
(select count(*) from (
SELECT jsonb_each(user_jsonb_column) FROM users WHERE username = $1
INTERSECT
SELECT jsonb_each(user_jsonb_column) FROM users WHERE username = $2
) as SAME_PAIRS
)::decimal / (
select count(*) from (
SELECT jsonb_object_keys(user_jsonb_column) FROM users WHERE username = $1
INTERSECT
SELECT jsonb_object_keys(user_jsonb_column) FROM users WHERE username = $2
) as SAME_KEYS
)
* 100) as similarity_percentage
$function$
Then I can execute this function:
SELECT calculate_similarity_percentage('johndoe','janedoe')
And it returns this without any problem:
similarity_percentage
62
However, I would like Hasura to track this function so that I can query it on graphQL as:
query MyQuery {
calculate_similarity_percentage(args: {user1: "johndoe", user2: "janedoe"}) {
similarity_percentage
}
}
But if I try to track the function above, Hasura says:
**SQL Execution Failed**
in function "calculate_similarity_percentage":
the function "calculate_similarity_percentage" cannot be tracked for the following reasons:
• the function does not return a "COMPOSITE" type
• the function does not return a SETOF
• the function does not return a SETOF table
I have no idea if I can find a workaround and return a numeric value as a "COMPOSITE" or SETOF table.

Answer 1

Here is how I kind of solved my case. But this was not the optimal solution so I'm not accepting this as an answer.
I ended up creating another table like this:
USER_RELATION_TABLE:
| user1_col | user2_col |
|--------------------------|
| 'johndoe' | 'janedoe' |
|--------------------------|
| 'brad' | 'angelina' |
|--------------------------|
| ... | ... |
Then I added a computed field on the relation table with the following function:
CREATE OR REPLACE FUNCTION public.calculate_similarity_percentage(user_relation_row user_relation_table)
RETURNS numeric
LANGUAGE sql
STABLE
AS $function$
SELECT ROUND(
(select count(*) from (
SELECT jsonb_each(user_jsonb_column) FROM users
WHERE username = user_relation_row.user1_col
INTERSECT
SELECT jsonb_each(user_jsonb_column) FROM users
WHERE username = user_relation_row.user2_col
) as SAME_PAIRS
)::decimal / (
select count(*) from (
SELECT jsonb_object_keys(user_jsonb_column) FROM users
WHERE username = user_relation_row.user1_col
INTERSECT
SELECT jsonb_object_keys(user_jsonb_column) FROM users
WHERE username = user_relation_row.user2_col
) as SAME_KEYS
)
* 100) as similarity_percentage
$function$
Now I can query it on the graphQL like this:
query MyQuery {
user_relation_table {
similarity
}
}