c# - 如何使用 LINQ 在 DTO 中填充集合？

Question

我创建了以下 DTO:

    public class TestAndQuestionDTO
    {
        public string Name { get; set; }
        public int QuestionsCount { get; set; }
        public ICollection<TestAndQuestionDTO.Questions> TestQuestions { get; set; }

        public class Questions
        {
            public Guid QuestionUId { get; set; }
        }
    }

我正在尝试使用 LINQ 填充它，但我对如何填充内部 Questions 类感到困惑。

这是我目前所拥有的:

    var result = await db.Tests
            .Include(t => t.TestQuestions)
            .Where(t => t.TestId == id)
            .Select(t => new TestAndQuestionDTO
            {
                Name = t.Title,
                TestQuestions = new TestAndQuestionDTO.Questions
                {
                    QuestionUId = t.TestQuestions. ????
                }

            })
            .ToListAsync();

有人可以告诉我如何使用从我的集合中带回的数据填充 TestQuestions 集合字段:.Include(t => t.TestQuestions) 我必须例如有TestAndQuestionDTO 中的构造函数来创建 TestQuestions 的集合？

这是我的测试类以供引用:

public partial class Test
{
    public Test()
    {
        this.TestQuestions = new HashSet<TestQuestion>();
    }

    public int TestId { get; set; }
    public string Title { get; set; }
    public virtual ICollection<TestQuestion> TestQuestions { get; set; }

}

Answer 1

您可以像这样使用另一个 Select 转换为您的问题 DTO:

var result = await db.Tests
        .Include(t => t.TestQuestions)
        .Where(t => t.TestId == id)
        .Select(t => new TestAndQuestionDTO
        {
            Name = t.Title,
            TestQuestions = t.TestQuestions.Select(tq => new TestAndQuestionDTO.Questions
            {
                QuestionUId = tq.QuestionUId,
                //fill in your Questions DTO here
            })

        })
        .ToListAsync();

如果需要TestAndQuestionDTO.Questions成为ICollection<>键入，将其更改为:

var result = await db.Tests
        .Include(t => t.TestQuestions)
        .Where(t => t.TestId == id)
        .Select(t => new TestAndQuestionDTO
        {
            Name = t.Title,
            TestQuestions = new Collection<TestAndQuestionDTO.Questions>(
                t.TestQuestions.Select(tq => new TestAndQuestionDTO.Questions
                {
                    QuestionUId = tq.QuestionUId,
                    //fill in your Questions DTO here
                }).ToList())
        })
        .ToListAsync();