travisf
Getting a specific page from Ecto Scrivener total_entries
I’m wondering if ecto_scrivener has a specific way of getting a entries from a specific page after %Scrivener.Page{} has already loaded.
For example if I run a query:
Record
|> my_query
|> Repo.paginate()
This will return all records. But then if I have pagination at the bottom of my page and I hit page two I’m effectively running:
Record
|> my_query
|> Repo.paginate(page: 2)
It seems silly to run the query two times when I already have all the records (especially if they are assigned in a conn or socket). I realize I I could divide the total records by the page_size and get the page number that way but I’m wondering if this is the preferred way or is there a better way?
Marked As Solved
sodapopcan
This isn’t something you would ever want to do without thinking through it carefully. For example, if you’re going to cache pages on the client then you have to worry about invalidating it. And if you’re talking about caching per request on the client, then I could turn your worry around on you and say: “What if they never navigate past page 1? Now you’ve gone and fetched too much data!” In any event, such queries are relatively cheap and I wouldn’t give optimizing them a second thought until your server is on fire 
In the past I’ve used sever-side caching (Varnish) for a product catalog and invalidated the whole cache any time we published new products. It was a minimal, but noticeable, difference in speed and was really just masking poor database design requiring far too many joins just to get some rows of available products.
In any event, you have an internal system so I would really not give this a second thought! One query per page is absolutely fine.
Also Liked
sodapopcan
Sorry to XY you but what are you you trying to do here? The usecase of loading all entries and then paging anyway is not one I’ve ever come across. I only know ecto_scrivener by name, but it seems your examples are missing some sort of per_page param. If Repo.paginate(query) returns everything yet Repo.paginate(query, page: 2) returns page 2, what is dictating how many results are being returned for the latter?
sodapopcan
That would make sense but OP said that it is returning all results, so that is why I was clarifying.
If you aren’t using Ash (which I am not yet either) then I say look no further than Flop and its cousin Flop Phoenix. It has a more functional API in that it returns a nested tuple instead of a struct. It took me a hot minute to get comfy with it since I was coming from Ruby pagination libs which are incredibly simple, but it’s worth it as it’s very powerful. Not only does it also do cursor-based pagination, it does filtering and sorting!
I swear I’m not the author, just a big fan!
Kurisu
Thank you for sharing your experience! At a first glance, Flop looks really full-featured. I will definitely give it a try!
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