Why does it need to find the source CMYK color in the DB? All the information from that row you either have or you can calculate without hitting the db, no? I mean, since your input is a CMYK color, you can just run the same mapping function on it and get the lightness/chroma/hue values corresponding to it - without touching the database.
Actually, do you even need the db for anything? If I understand correctly, it can go like this:
You are given an input CMYK values, a hue OR lightness OR chroma value and a scale factor,. Say you're given C,M,Y,K, attribute = "lightness" and scale_factor = 0.2 and direction = 1.
(a) convert the CMYK value you were given to H/L/C (running the mapping function).
(b) given a desired "smallest granularity" (e.g. one matching the precision you already have on the db), just run a loop on the H/L/C value you got in (a), incrementing L from its original value up to the max value you can go given the scale factor. For each step you have a new L value, say L' value, and you can combine it with H and C, to get: H, L', C. Convert that back to CMYK using a reverse mapping, and that's one of your answers. Increase L' another step and repeat.
