From a4792206f7a34ded7673ab180979eeecd1d0ffb6 Mon Sep 17 00:00:00 2001
From: Yared Yemane <yaredyemane1@gmail.com>
Date: Wed, 10 Jun 2026 05:26:17 -0700
Subject: [PATCH] fix: use two-phase bump when shifting sort_order on content
 insert

Co-authored-by: Cursor <cursoragent@cursor.com>
---
 internal/repository/lms_sort_order_shift.go | 86 +++++++++++++--------
 1 file changed, 54 insertions(+), 32 deletions(-)

diff --git a/internal/repository/lms_sort_order_shift.go b/internal/repository/lms_sort_order_shift.go
index 3e236ff..95c2ff1 100644
--- a/internal/repository/lms_sort_order_shift.go
+++ b/internal/repository/lms_sort_order_shift.go
@@ -9,61 +9,83 @@ import (
 // Sequential siblings (programs global, courses per program, modules per course, lessons per module) use unique sort_order.
 // These helpers move id from oldPos to newPos without collisions by temporarily assigning sort_order = -id then shifting intermediates.
 
-// shift*SortOrderForInsert makes room at fromPos by incrementing existing rows at/after that position.
-// Rows are updated highest-first so the unique (parent, sort_order) index is never violated mid-shift.
+// sortOrderInsertShiftBump moves affected rows into a high temporary range, then back to
+// (old + 1). A single UPDATE ... SET sort_order = sort_order + 1 can violate unique
+// (parent, sort_order) indexes because PostgreSQL does not apply row updates in sort order.
+const sortOrderInsertShiftBump = int32(1_000_000)
 
 func shiftProgramsSortOrderForInsert(ctx context.Context, tx pgx.Tx, fromPos int32) error {
+	bump := sortOrderInsertShiftBump
+	if _, err := tx.Exec(ctx, `
+UPDATE programs
+SET sort_order = sort_order + $2
+WHERE sort_order >= $1`, fromPos, bump); err != nil {
+		return err
+	}
 	_, err := tx.Exec(ctx, `
-UPDATE programs AS t
-SET sort_order = t.sort_order + 1
-FROM (
-    SELECT id FROM programs WHERE sort_order >= $1 ORDER BY sort_order DESC
-) AS s
-WHERE t.id = s.id`, fromPos)
+UPDATE programs
+SET sort_order = sort_order - $2
+WHERE sort_order >= $1`, bump, bump-1)
 	return err
 }
 
 func shiftCoursesSortOrderForInsert(ctx context.Context, tx pgx.Tx, programID int64, fromPos int32) error {
+	bump := sortOrderInsertShiftBump
+	if _, err := tx.Exec(ctx, `
+UPDATE courses
+SET sort_order = sort_order + $3
+WHERE program_id = $1 AND sort_order >= $2`, programID, fromPos, bump); err != nil {
+		return err
+	}
 	_, err := tx.Exec(ctx, `
-UPDATE courses AS t
-SET sort_order = t.sort_order + 1
-FROM (
-    SELECT id FROM courses WHERE program_id = $1 AND sort_order >= $2 ORDER BY sort_order DESC
-) AS s
-WHERE t.id = s.id`, programID, fromPos)
+UPDATE courses
+SET sort_order = sort_order - $3
+WHERE program_id = $1 AND sort_order >= $2`, programID, bump, bump-1)
 	return err
 }
 
 func shiftModulesSortOrderForInsert(ctx context.Context, tx pgx.Tx, courseID int64, fromPos int32) error {
+	bump := sortOrderInsertShiftBump
+	if _, err := tx.Exec(ctx, `
+UPDATE modules
+SET sort_order = sort_order + $3
+WHERE course_id = $1 AND sort_order >= $2`, courseID, fromPos, bump); err != nil {
+		return err
+	}
 	_, err := tx.Exec(ctx, `
-UPDATE modules AS t
-SET sort_order = t.sort_order + 1
-FROM (
-    SELECT id FROM modules WHERE course_id = $1 AND sort_order >= $2 ORDER BY sort_order DESC
-) AS s
-WHERE t.id = s.id`, courseID, fromPos)
+UPDATE modules
+SET sort_order = sort_order - $3
+WHERE course_id = $1 AND sort_order >= $2`, courseID, bump, bump-1)
 	return err
 }
 
 func shiftLessonsSortOrderForInsert(ctx context.Context, tx pgx.Tx, moduleID int64, fromPos int32) error {
+	bump := sortOrderInsertShiftBump
+	if _, err := tx.Exec(ctx, `
+UPDATE lessons
+SET sort_order = sort_order + $3
+WHERE module_id = $1 AND sort_order >= $2`, moduleID, fromPos, bump); err != nil {
+		return err
+	}
 	_, err := tx.Exec(ctx, `
-UPDATE lessons AS t
-SET sort_order = t.sort_order + 1
-FROM (
-    SELECT id FROM lessons WHERE module_id = $1 AND sort_order >= $2 ORDER BY sort_order DESC
-) AS s
-WHERE t.id = s.id`, moduleID, fromPos)
+UPDATE lessons
+SET sort_order = sort_order - $3
+WHERE module_id = $1 AND sort_order >= $2`, moduleID, bump, bump-1)
 	return err
 }
 
 func shiftExamPrepUnitsSortOrderForInsert(ctx context.Context, tx pgx.Tx, catalogCourseID int64, fromPos int32) error {
+	bump := sortOrderInsertShiftBump
+	if _, err := tx.Exec(ctx, `
+UPDATE exam_prep.units
+SET sort_order = sort_order + $3
+WHERE catalog_course_id = $1 AND sort_order >= $2`, catalogCourseID, fromPos, bump); err != nil {
+		return err
+	}
 	_, err := tx.Exec(ctx, `
-UPDATE exam_prep.units AS t
-SET sort_order = t.sort_order + 1
-FROM (
-    SELECT id FROM exam_prep.units WHERE catalog_course_id = $1 AND sort_order >= $2 ORDER BY sort_order DESC
-) AS s
-WHERE t.id = s.id`, catalogCourseID, fromPos)
+UPDATE exam_prep.units
+SET sort_order = sort_order - $3
+WHERE catalog_course_id = $1 AND sort_order >= $2`, catalogCourseID, bump, bump-1)
 	return err
 }