public static CategoryTreeDTO ToDTO(Category category)
        {
            var categoryDTO = new CategoryTreeDTO
            {
                Id     = category.Id,
                Name   = category.Name,
                Status = category.Status
            };

            categoryDTO.Topics = category.Topics.Select(x => TopicTreeDTO.ToDTO(x)).ToList();
//            categoryDTO.Topics = context.Topics.Where(x => x.Id == categoryDTO.Id).Select(x => TopicTreeDTO.ToDTO(x, context)).ToList();
            return(categoryDTO);
        }
        public static TopicTreeDTO ToDTO(Topic topic)
        {
            var topicDTO = new TopicTreeDTO
            {
                Id     = topic.Id,
                Name   = topic.Name,
                Status = topic.Status,
            };

            topicDTO.Messages = topic.Messages.Select(x => MessageTreeDTO.ToDTO(x)).ToList();
//            topicDTO.Messages = context.Messages.Where(x => x.TopicId == topicDTO.Id).Select(x => MessageTreeDTO.ToDTO(x)).ToList();
            return(topicDTO);
        }