delete method
删除数据
Implementation
@override
Future<int> delete(T? t, [String? tableName]) {
if (t == null) return Future.value(-1);
Map<String, dynamic> map = t.primaryKeyAndValue();
return db.delete(
tableName ?? table,
where: "${map.keys.first} = ?",
whereArgs: [map.values.first],
);
}