Partials And Cache

Overview

Discord events can contain optional objects or only the IDs needed to identify them. In discord.go, these shapes appear as pointers such as Interaction.User, Interaction.Member, Interaction.Channel, and Interaction.Guild; there is no separate Discord.js-style partials manager. Treat absent pointers as normal, then use the optional cache and REST fetch helpers when a complete resource is needed.

Tutorial: Cache-Aside Fetch

1. Create a bounded cache.MemoryCache with a TTL.
2. Attach it using bot.WithCache.
3. Try CachedUser, CachedMember, or another typed lookup.
4. On a miss, call FetchUser, FetchMember, or a matching method with a timeout.
5. Treat the returned object as a snapshot and invalidate or refetch after mutations.

The built-in cache implements guild, channel, user, role, message, and member typed interfaces. A custom cache can implement only the interfaces its application needs.

Complete Runnable Example

Copy to examples/partials-cache/main.go, set DISCORD_TOKEN, and run it. Invoke /user-cache with a user option twice.

package main

import (
	"context"
	"fmt"
	"log"
	"os"
	"time"

	"github.com/discord-go/discord.go/bot"
	"github.com/discord-go/discord.go/cache"
	"github.com/discord-go/discord.go/intents"
	"github.com/discord-go/discord.go/interactions"
)

func main() {
	token := os.Getenv("DISCORD_TOKEN")
	if token == "" {
		log.Fatal("DISCORD_TOKEN is required")
	}

	router := bot.NewRouter()
	router.Command("user-cache", "Inspect a cached user", func(ctx *bot.InteractionContext) {
		userID := ctx.GetUserID("user")
		if userID == 0 {
			_ = ctx.ReplyEphemeral("A user is required.")
			return
		}
		if user, ok := ctx.Bot.CachedUser(userID); ok {
			_ = ctx.Reply(fmt.Sprintf("Cache hit: %s", user.Username))
			return
		}
		requestCtx, cancel := context.WithTimeout(ctx.Context(), 5*time.Second)
		defer cancel()
		user, err := ctx.Bot.FetchUser(requestCtx, userID)
		if err != nil {
			log.Printf("fetch user: %v", err)
			_ = ctx.ReplyEphemeral("The user could not be fetched.")
			return
		}
		_ = ctx.Reply(fmt.Sprintf("Cache miss; fetched %s", user.Username))
	}, interactions.ApplicationCommandOption{
		Type:        interactions.ApplicationCommandOptionTypeUser,
		Name:        "user",
		Description: "The user to fetch",
		Required:    true,
	})

	store := cache.NewMemoryCache(cache.WithTTL(10*time.Minute), cache.WithMaxSize(10000))
	b := bot.New(token, bot.WithIntents(intents.Guilds), bot.WithCache(store), bot.WithRouter(router))
	if err := b.Run(); err != nil {
		log.Fatal(err)
	}
}

Optional Data Rules

Always nil-check Member, User, Channel, and Guild pointers. A DM has no guild or member. A cache hit is not authoritative permission data, and a cache miss does not prove that a resource does not exist. Use FetchMember or another REST call when the operation requires fresh data.

Common Mistakes

• Dereferencing an optional event pointer without checking it.
• Configuring a cache but ignoring the hit boolean.
• Using an unlimited cache for a large, long-running bot.
• Assuming Gateway hydration covers data for unrequested intents.
• Using stale cached permissions for a destructive action.

Expected Result

The first /user-cache call fetches and stores the selected user. A later call can use the typed cache hit until the TTL expires.

Related Pages

• Gateway Intents
• Permissions
• Common Errors