Dependant variable not working

[barsdeveloper]

Hello, I've been trying for a long time to make setup a variable whose query depends on another variable and couldn't. The only explanation I have is that there is a bug somewhere.

This is my table

CREATE TABLE IF NOT EXISTS ao_pricing.data (
    model_instrument uuid,
    maturity bigint,
    as_of timestamp,
    label ascii static,
    pricer_data pricer_data_t,
    fitter_data fitter_data_t,
    PRIMARY KEY ((model_instrument, maturity), as_of)
) WITH CLUSTERING ORDER BY (as_of DESC);

Please notice I have a partition key which is composed of two keys: model_instrument and maturity. My temporal variable is: as_of.

Now I want to show in Grafana graphs that depend on the pair (model_instrument, maturity) which must be selectable through a dropdown and this would be my parameter for the queries.

There are multiple problems with this. First is that I don't know how to return a pair or tuple for variables. The ideal query to get all the parameter values would be:

SELECT DISTINCT model_instrument, maturity, label FROM ao_pricing.data;

It returns results like this:

cqlsh> SELECT DISTINCT model_instrument, maturity, label FROM ao_pricing.data;

 model_instrument                     | maturity            | label
--------------------------------------+---------------------+-----------------------------
 e971637a-9454-11e1-a34e-15ebadefba03 | 1704472200000000000 |             INGA 2024-01-05
 ea14f940-9454-11e1-a34e-15ebadefba03 | 1704472200000000000 |             RDSA 2024-01-05
 e9a7721c-9454-11e1-a34e-15ebadefba03 | 1718983800000000000 |              VOW 2024-06-21
 e971637a-9454-11e1-a34e-15ebadefba03 | 1710520200000000000 |             INGA 2024-03-15
 e95fa338-9454-11e1-a34e-15ebadefba03 | 1718983800000000000 |              BAS 2024-06-21
 e95fa338-9454-11e1-a34e-15ebadefba03 | 1726846200000000000 |              BAS 2024-09-20

Now if I define a variable, it expects to get two columns: one is the value and one is the text. My query would return 3, I can't make the value a pair or tuple. I came up with a work around leveraging the functions from ScyllaDB (let me know if you have a better solution for this):

CREATE OR REPLACE FUNCTION ao_pricing.pair_to_key(a ascii, b ascii)
  RETURNS NULL ON NULL INPUT
  RETURNS ascii
  LANGUAGE LUA
  AS 'return a.."|"..b;';

So I changed and now I have two variables, first query is be the following (products):

SELECT DISTINCT pair_to_key(pair_to_key(CAST(model_instrument AS ascii), CAST(maturity AS ascii)), label) FROM ao_pricing.data;

and second query is:

SELECT DISTINCT pair_to_key(pair_to_key(CAST(model_instrument AS ascii), CAST(maturity AS ascii)), label) FROM ao_pricing.data WHERE model_instrument = $products ALLOW FILTERING;

But this does not work, I always get an error: Error updating options: JSON.parse: unexpected end of data at line 1 column 1 of the JSON data.

Do you have a solution: I can either keep the two variables separated OR I can keep one variable but in that case I need to extract the first part of the concatenation (and this seems to be impossible to do in Grafana).

[unflag]

Hi, @barsdeveloper !
Thank you for your report. It is true that dependant variables are not supported by the datasource yet.
I believe that in your case there is no other way than to use separated variables.

[HadesArchitect]

@unflag Do you think it'll be hard to implement? I have some free time now.

[porresp]

Hello, any update on this issue? Thanks.

[unflag]

@HadesArchitect It is the subject to research. I am sure there is a way since the prometheus datasource support template variables. I believe it has to be done somewhere in plugins frontend, because backend resolves variables independently. Probable, it would be better to look into existing plugins(e.g. prometheus) first.