How do I query the '/chapter'-route with blacklisted chapter ids? Can only find a way to whitelist.

Dex-chan lover
Jan 2, 2019
As title states, this is a question about the '/chapter'-route.
To be clear, that is the route simply listing all chapters metadata, not the one for actually downloading chapters.

I figured I should 'optimize' my userscript a bit to try and give the API-backend a break by avoiding asking for already seen chapters in my queries.
To be exact, I have a couple "filters" (that are not entirely mutually exclusive, nor necessarily inclusive), which I use the API-params to filter things so I can reduce my amount of fetches and thus load put on db. And as I want to further reduce that load, I would ideally want to be able to tell the second filters queries to exclude the chapter-ids seen in the first.

The '/chapter/?ids[]=' param can be used to whitelist the exact chapters you want to see (up to 100), but I found no equivalent 'excludedIds[]=' param, similar to 'excludedGroups[]='. Does it not exist, am I blind when reading docs, or is such a blacklist undocumented?

Granted, if such a blacklist-param had the same limit of 100 as ids[] (which it probably wouldn't, as comparing to excludedGroups[] we see no such limit) it wouldn't be terribly useful either way (As it's not uncommon for a filter to have seen 2k+ chapters if user hasn't caught up on chapter in a week+).
But at least it would reduce the pagination by up to [a single] query(ies)!
Though I am unsure whether that is enough to actually reduce load, or whether the backend would instead actually experience more load when all the queries include such a list of 100 extra params in their n queries (if they had to paginate 2k results, that would be n=20) just to avoid performing 1 extra query :p

Overall, I am not wholly convinced it's actually all that useful even if uncapped (For the backend, that is. Due to the rate-limits it would definitely still be useful for the client). As when filter A has had n pages of results (n*100 results), if filter B then ends up having a sizeable overlap (lets pick the maximum: 100% of A appears in B) and additionally needs to paginate m pages of new results.
When excluding, that is n+m pages in total to paginate (filter A + (B-A)), where for m of those pages the blacklist is used, giving a total of m*n of those params for backend to handle (n per page). While had they not been excluded, B would only have had n extra pages to paginate (a total of m+n pages of results for filter B).
So in conclusion n more queries in return for not having those "extra" m*n params to handle. (At 0% overlap it would be 0 extra queries).
For the client that is a steal (n/5 fewer seconds to retrieve data. Even larger time-save if we account for fetching one cover for each unique manga id), but for the backend it really depends on the cost of the parse+filter operation vs handling extra queries. Which would depend on implementation, and could be everything from super cheap, to horribly costly.