fix(sqlite): preserve channel references during migration

SQLite executes ON DELETE actions when the migration drops the channel table with foreign keys enabled. Pause enforcement around an explicit transactional rebuild, preserve channel rows on rollback, and cover both directions with the real embedded migration.

Author: D3SOX

migrations/sqlite/2026-08-18-132346-0000_channel/down.sql

@@ -1,8 +1,17 @@
-DROP TABLE IF EXISTS channel;
-CREATE TABLE channel
+PRAGMA foreign_keys = OFF;
+BEGIN;
+
+CREATE TABLE channel_temp
 (
     id VARCHAR(24) PRIMARY KEY NOT NULL,
     name VARCHAR NOT NULL,
     avatar VARCHAR NOT NULL,
     verified BOOLEAN NOT NULL
 );
+INSERT INTO channel_temp
+SELECT id, name, COALESCE(avatar, ''), verified FROM channel;
+DROP TABLE channel;
+ALTER TABLE channel_temp RENAME TO channel;
+
+COMMIT;
+PRAGMA foreign_keys = ON;

migrations/sqlite/2026-08-18-132346-0000_channel/metadata.toml

@@ -0,0 +1 @@
+run_in_transaction = false

migrations/sqlite/2026-08-18-132346-0000_channel/up.sql

@@ -1,5 +1,11 @@
--- make avatar url nullable
--- https://stackoverflow.com/questions/4007014/alter-column-in-sqlite
+-- Rebuilding the parent table while foreign keys are enabled would execute the
+-- ON DELETE actions and erase rows that reference channels. This migration runs
+-- outside Diesel's transaction so the first PRAGMA takes effect, then wraps the
+-- rebuild in its own transaction.
+PRAGMA foreign_keys = OFF;
+BEGIN;
+
+-- Make avatar nullable.
 CREATE TABLE channel_temp
 (
     id VARCHAR(24) PRIMARY KEY NOT NULL,
@@ -10,3 +16,6 @@ CREATE TABLE channel_temp
 INSERT INTO channel_temp SELECT * FROM channel;
 DROP TABLE channel;
 ALTER TABLE channel_temp RENAME TO channel;
+
+COMMIT;
+PRAGMA foreign_keys = ON;

src/main.rs

@@ -278,6 +278,36 @@ async fn run_migrations(pool: &DbPool, database_url: &str, approval: Option<&str
 mod tests {
     use super::require_migration_approval;
 
+    #[cfg(feature = "sqlite")]
+    #[derive(diesel::QueryableByName)]
+    struct RowCount {
+        #[diesel(sql_type = diesel::sql_types::BigInt)]
+        count: i64,
+    }
+
+    #[cfg(feature = "sqlite")]
+    fn table_count(conn: &mut diesel::SqliteConnection, table: &str) -> i64 {
+        use diesel::RunQueryDsl;
+
+        diesel::sql_query(format!("SELECT COUNT(*) AS count FROM {table}"))
+            .get_result::<RowCount>(conn)
+            .unwrap()
+            .count
+    }
+
+    #[cfg(feature = "sqlite")]
+    fn foreign_keys_enabled(conn: &mut diesel::SqliteConnection) -> bool {
+        use diesel::RunQueryDsl;
+
+        diesel::sql_query(
+            "SELECT COUNT(*) AS count FROM pragma_foreign_keys WHERE foreign_keys = 1",
+        )
+        .get_result::<RowCount>(conn)
+        .unwrap()
+        .count
+            == 1
+    }
+
     #[test]
     fn fresh_database_does_not_require_approval() {
         assert!(require_migration_approval(false, &["20260721".to_owned()], None).is_ok());
@@ -290,4 +320,48 @@ mod tests {
         assert!(require_migration_approval(true, &pending, Some("20260721")).is_err());
         assert!(require_migration_approval(true, &pending, Some("20260721,20260722")).is_ok());
     }
+
+    #[cfg(feature = "sqlite")]
+    #[test]
+    fn channel_migration_preserves_referencing_rows() {
+        use diesel::Connection;
+        use diesel::connection::SimpleConnection;
+        use diesel_migrations::MigrationHarness;
+
+        let mut conn = diesel::SqliteConnection::establish(":memory:").unwrap();
+        conn.batch_execute("PRAGMA foreign_keys = ON;").unwrap();
+
+        let migrations = conn.pending_migrations(super::MIGRATIONS).unwrap();
+        let channel_migration = migrations
+            .iter()
+            .position(|migration| migration.name().version().to_string() == "202608181323460000")
+            .expect("channel migration must be embedded");
+
+        conn.run_migrations(&migrations[..channel_migration])
+            .unwrap();
+        conn.batch_execute(
+            "INSERT INTO channel (id, name, avatar, verified) \
+             VALUES ('channel-1', 'Channel', 'https://example.test/avatar', false); \
+             INSERT INTO video (id, title, upload_date, uploader_id, thumbnail_url, duration) \
+             VALUES ('video-1', 'Video', 0, 'channel-1', \
+                     'https://example.test/thumbnail', 60);",
+        )
+        .unwrap();
+
+        assert_eq!(table_count(&mut conn, "video"), 1);
+        conn.run_migration(migrations[channel_migration].as_ref())
+            .unwrap();
+        assert!(foreign_keys_enabled(&mut conn));
+        assert_eq!(table_count(&mut conn, "channel"), 1);
+        assert_eq!(table_count(&mut conn, "video"), 1);
+
+        conn.batch_execute("UPDATE channel SET avatar = NULL;")
+            .unwrap();
+        conn.revert_migration(migrations[channel_migration].as_ref())
+            .unwrap();
+        assert!(foreign_keys_enabled(&mut conn));
+        assert_eq!(table_count(&mut conn, "channel"), 1);
+        assert_eq!(table_count(&mut conn, "video"), 1);
+        assert_eq!(table_count(&mut conn, "pragma_foreign_key_check"), 0);
+    }
 }