如何使用 LINQ 填充 DTO 内的集合？

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 填充此内容，但我被困在如何填充内部 Questions 类上。

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();

谁能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) 例如，我是否必须在 TestAndQuestionDTO 中有一个构造函数来创建一个 TestQuestions 集合？

这是我的测试类供参考：

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 Questions 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();

如果您需要 TestAndQuestionDTO.Questions 为 ICollection<> 类型，请将其更改为：

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();