Rollback on constraint failure

sqlite3.go

@@ -494,10 +494,12 @@ func (ai *aggInfo) Done(ctx *C.sqlite3_context) {
 // Commit transaction.
 func (tx *SQLiteTx) Commit() error {
 	_, err := tx.c.exec(context.Background(), "COMMIT", nil)
-	if err != nil && err.(Error).Code == C.SQLITE_BUSY {
-		// sqlite3 will leave the transaction open in this scenario.
+	if err != nil {
+		// sqlite3 may leave the transaction open in this scenario.
 		// However, database/sql considers the transaction complete once we
 		// return from Commit() - we must clean up to honour its semantics.
+		// We don't know if the ROLLBACK is strictly necessary, but according
+		// to sqlite's docs, there is no harm in calling ROLLBACK unnecessarily.
 		tx.c.exec(context.Background(), "ROLLBACK", nil)
 	}
 	return err

sqlite3_test.go

@@ -248,6 +248,43 @@ func TestForeignKeys(t *testing.T) {
 	}
 }
 
+func TestDeferredForeignKey(t *testing.T) {
+	fname := TempFilename(t)
+	uri := "file:" + fname + "?_foreign_keys=1"
+	db, err := sql.Open("sqlite3", uri)
+	if err != nil {
+		os.Remove(fname)
+		t.Errorf("sql.Open(\"sqlite3\", %q): %v", uri, err)
+	}
+	_, err = db.Exec("CREATE TABLE bar (id INTEGER PRIMARY KEY)")
+	if err != nil {
+		t.Errorf("failed creating tables: %v", err)
+	}
+	_, err = db.Exec("CREATE TABLE foo (bar_id INTEGER, FOREIGN KEY(bar_id) REFERENCES bar(id) DEFERRABLE INITIALLY DEFERRED)")
+	if err != nil {
+		t.Errorf("failed creating tables: %v", err)
+	}
+	tx, err := db.Begin()
+	if err != nil {
+		t.Errorf("Failed to begin transaction: %v", err)
+	}
+	_, err = tx.Exec("INSERT INTO foo (bar_id) VALUES (123)")
+	if err != nil {
+		t.Errorf("Failed to insert row: %v", err)
+	}
+	err = tx.Commit()
+	if err == nil {
+		t.Errorf("Expected an error: %v", err)
+	}
+	_, err = db.Begin()
+	if err != nil {
+		t.Errorf("Failed to begin transaction: %v", err)
+	}
+
+	db.Close()
+	os.Remove(fname)
+}
+
 func TestRecursiveTriggers(t *testing.T) {
 	cases := map[string]bool{
 		"?_recursive_triggers=1": true,