From 08c3a6e77a3f61ffc9643a5e1f840df9078d0b36 Mon Sep 17 00:00:00 2001
From: Owen Jacobson <owen@grimoire.ca>
Date: Fri, 27 Sep 2024 21:25:15 -0400
Subject: Assign sequence numbers from a counter, not by scanning messages

---
 src/events/repo/message.rs | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

(limited to 'src')

diff --git a/src/events/repo/message.rs b/src/events/repo/message.rs
index ec17d55..f6fce0e 100644
--- a/src/events/repo/message.rs
+++ b/src/events/repo/message.rs
@@ -4,7 +4,7 @@ use crate::{
     clock::DateTime,
     events::types::{self, Sequence},
     repo::{
-        channel::Channel,
+        channel::{self, Channel},
         login::{self, Login},
         message,
     },
@@ -30,7 +30,7 @@ impl<'c> Events<'c> {
         body: &str,
         sent_at: &DateTime,
     ) -> Result<types::ChannelEvent, sqlx::Error> {
-        let sequence = self.next_sequence_for(channel).await?;
+        let sequence = self.assign_sequence(&channel.id).await?;
 
         let id = message::Id::generate();
 
@@ -72,20 +72,20 @@ impl<'c> Events<'c> {
         Ok(message)
     }
 
-    async fn next_sequence_for(&mut self, channel: &Channel) -> Result<Sequence, sqlx::Error> {
-        let current = sqlx::query_scalar!(
+    async fn assign_sequence(&mut self, channel: &channel::Id) -> Result<Sequence, sqlx::Error> {
+        let next = sqlx::query_scalar!(
             r#"
-                -- `max` never returns null, but sqlx can't detect that
-                select max(sequence) as "sequence!: Sequence"
-                from message
-                where channel = $1
+                update channel
+                set last_sequence = last_sequence + 1
+                where id = $1
+                returning last_sequence as "next_sequence: Sequence"
             "#,
-            channel.id,
+            channel,
         )
         .fetch_one(&mut *self.0)
         .await?;
 
-        Ok(current.next())
+        Ok(next)
     }
 
     pub async fn expire(&mut self, expire_at: &DateTime) -> Result<(), sqlx::Error> {
-- 
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