Hello all, I’m doing a DB call for the index page of a WhatsApp-style chat app. I have ChatsUsers → Chats → Messages. I need to get the list of the user’s chats ordered by recency of the last_message, and just for the first Chat preload all of its Messages. See below for reference. [image] Her…

Why “preload” the messages in the first place? I’d load load those messages separately (in liveview components are great for that).

I thought this would save a DB query and be more performant. Is that not the case?

Hello! For my use case I used this: threads # list of structs |> MyApp.Repo.preload(messages: {MyApp.Chat.recent_messages_in_thread(), [:author]}) defmodule MyApp.Chat do def recent_messages_in_thread(query \\ MyApp.Chat.Message) do from messages in query, distinct: messages.thread_id…

Thanks for this, I’m not seeing where it loads only the recent messages for the first thread?

[image] Owens: I thought this would save a DB query and be more performant. Is that not the case? Unless you’re joining data in the query preloading will do additional queries as well. You could join messages only for your first chat, but this would need you knowing which chat the first one i…

You could join messages only for your first chat, but this would need you knowing which chat the first one Thanks, assuming we know the first one how would we preload just that?

Preloading is the act of loading associations for ecto schemas. This can happen in multiple ways, but the default is that associations are loaded in separate queries. So no more performant than a manual query for the messages of your first chat. The only thing potentially making preloads more perfo…

Preload only first nested association's association

Questions & Help Questions

fuelen November 16, 2020, 12:00pm 9

Actually, my snipped loads only the last message for every thread.