From bb8afd231de7c9beb36b9da1670c6189d64b8c96 Mon Sep 17 00:00:00 2001
From: kim <grufwub@gmail.com>
Date: Tue, 11 Feb 2025 14:30:05 +0000
Subject: [PATCH] updates the enum migration to perform a singular update for
 all values, using an SQL case statement

---
 internal/db/bundb/migrations/util.go | 42 +++++++++++++++++-----------
 1 file changed, 26 insertions(+), 16 deletions(-)

diff --git a/internal/db/bundb/migrations/util.go b/internal/db/bundb/migrations/util.go
index edf7c1d05..033150ad6 100644
--- a/internal/db/bundb/migrations/util.go
+++ b/internal/db/bundb/migrations/util.go
@@ -35,6 +35,11 @@ import (
 	"github.com/uptrace/bun/schema"
 )
 
+// formatQuery formats given query + args according to given bun dialect, using for debug logging.
+func formatQuery(d schema.Dialect, query string, args ...any) string {
+	return schema.NewFormatter(d).FormatQuery(query, args...)
+}
+
 // convertEnums performs a transaction that converts
 // a table's column of our old-style enums (strings) to
 // more performant and space-saving integer types.
@@ -82,26 +87,31 @@ func convertEnums[OldType ~string, NewType ~int16](
 		return gtserror.Newf("error selecting total count: %w", err)
 	}
 
-	var updated int
+	var args []any
+	var qbuf byteutil.Buffer
+
+	// Prepare a singular UPDATE statement using
+	// SET $newColumn = (CASE $column WHEN $old THEN $new ... END)
+	qbuf.WriteString("UPDATE ? SET ? = (CASE ? ")
+	args = append(args, bun.Ident(table))
+	args = append(args, bun.Ident(newColumn))
+	args = append(args, bun.Ident(column))
 	for old, new := range mapping {
+		qbuf.WriteString("WHEN ? THEN ? ")
+		args = append(args, old, new)
+	}
+	qbuf.WriteString("ELSE ? END)")
+	args = append(args, *defaultValue)
 
-		// Update old to new values.
-		res, err := tx.NewUpdate().
-			Table(table).
-			Where("? = ?", bun.Ident(column), old).
-			Set("? = ?", bun.Ident(newColumn), new).
-			Exec(ctx)
-		if err != nil {
-			return gtserror.Newf("error updating old column values: %w", err)
-		}
-
-		// Count number items updated.
-		n, _ := res.RowsAffected()
-		updated += int(n)
+	// Execute the prepared raw query with arguments.
+	res, err := tx.NewRaw(qbuf.String(), args...).Exec(ctx)
+	if err != nil {
+		return gtserror.Newf("error updating old column values: %w", err)
 	}
 
-	// Check total updated.
-	if total != updated {
+	// Count number items updated.
+	updated, _ := res.RowsAffected()
+	if total != int(updated) {
 		log.Warnf(ctx, "total=%d does not match updated=%d", total, updated)
 	}