feat(dbal): add proper insert ignore conflict method for MySQL

Signed-off-by: Benjamin Gaussorgues <benjamin.gaussorgues@nextcloud.com>

lib/private/DB/AdapterMySQL.php

@@ -35,4 +35,32 @@ class AdapterMySQL extends Adapter {
 
 		return $this->collation;
 	}
+
+	public function insertIgnoreConflict(string $table, array $values): int {
+		$builder = $this->conn->getQueryBuilder();
+		$builder->insert($table);
+		$updates = [];
+		foreach ($values as $key => $value) {
+			$builder->setValue($key, $builder->createNamedParameter($value));
+		}
+
+		/*
+		 * We can't use ON DUPLICATE KEY UPDATE here because Nextcloud use the CLIENT_FOUND_ROWS flag
+		 * With this flag the MySQL returns the number of selected rows
+		 * instead of the number of affected/modified rows
+		 * It's impossible to change this behaviour at runtime or for a single query
+		 * Then, the result is 1 if a row is inserted and also 1 if a row is updated with same or different values
+		 *
+		 * With INSERT IGNORE, the result is 1 when a row is inserted, 0 otherwise
+		 *
+		 * Risk: it can also ignore other errors like type mismatch or truncated data…
+		 */
+		$res = $this->conn->executeStatement(
+			preg_replace('/^INSERT/i', 'INSERT IGNORE', $builder->getSQL()),
+			$builder->getParameters(),
+			$builder->getParameterTypes()
+		);
+
+		return $res;
+	}
 }