Question

我试图通过一对多的关系来获取我的数据库的值我有这样的对象

学生

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                        });
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            <script src="http://code.jquery.com/jquery-latest.js"></script>
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          <script>
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                $('#dataTables-example').DataTable({
                        responsive: true
                });
            });
            </script>

注册

[Table("Student")]
    public class Student  : IStudent
    {    

        public int Id { get; set; }
        public string Lastname { get; set; }
        public string FirstMidName { get; set; }
        public DateTime? EnrollmentDate { get; set; }

        [Write(false)]
        public IEnumerable<Enrollment> Enrollments { get; set; }
    }

场

[Table("Enrollment")]
    public class Enrollment
    {
        public int Id { get; set; }
        public int CourseId { get; set; }
        public int StudentId { get; set; }
        public string Grade { get; set; }
        public virtual Course Course { get; set; }
        public virtual Student Student { get; set; }
    }

这是我的短小精悍的代码

[Table("Course")]
public class Course
{   
    public int Id { get; set; }
    public string Title { get; set; }
    public int Credits { get; set; }
    public virtual IEnumerable<Enrollment> Enrollments { get; set; }
}

根据指令Here我所要做的就是扩展3级层次结构，但我不能让它工作

这是我的带有映射器的GridReader

_connection = Connect.GetOpenConnection();
        const string query = @"SELECT * FROM Student stu where id = @id " +
                             "SELECT * FROM Enrollment enr WHERE enr.StudentId in (SELECT id FROM Student stu where id = @id) " +
                             "SELECT * FROM Course cou WHERE cou.Id in (SELECT CourseId from Enrollment where StudentId = @id)";

        var result = _connection.QueryMultiple(query, new { id = id })
            .Map<Student, Enrollment, Course, int>(
                student => student.Id,     
                enrollment => enrollment.StudentId,
                course=>course.Id,
                (student, enrollments) => student.Enrollments = enrollments ,
                (student, courses) => student.Enrollments.ForEach(s=>courses.ForEach(x=>s.Course.Title = x.Title) )
            ).FirstOrDefault();

当我在这里运行我的应用程序时，ID为1的结果通知课程标题没有值。我希望你能帮助我，谢谢你。

更新1

我注意到我在这里得到空值，它没有进入if语句

public static IEnumerable<TFirst> Map<TFirst, TSecond, TThird, TKey>
        (
        this SqlMapper.GridReader reader,
        Func<TFirst, TKey> firstKey,
        Func<TSecond, TKey> secondKey,
        Func<TThird, TKey> thirdKey,
        Action<TFirst, IEnumerable<TSecond>> addSecond,
        Action<TFirst, IEnumerable<TThird>> addThird
        )
    {
        var result = reader.Read<TFirst>().ToList();

        var secondMap = reader
            .Read<TSecond>()
            .GroupBy(s=>secondKey(s))
            .ToDictionary(g => g.Key, g => g.AsEnumerable());

        var thirdMap = reader
           .Read<TThird>()
           .GroupBy(t => thirdKey(t))
           .ToDictionary(g => g.Key, g => g.AsEnumerable());     


        foreach (var item in result)
        {
            IEnumerable<TThird> third;
            if (thirdMap.TryGetValue(firstKey(item), out third))
            {
                addThird(item, third);
            }

            IEnumerable<TSecond> second;
            if (secondMap.TryGetValue(firstKey(item), out second))
            {
                addSecond(item, second);
            }

        }



        return result.ToList();
    }

更新2

我在这里解决的问题是我做的事情

IEnumerable<TSecond> second;
        if (secondMap.TryGetValue(firstKey(item), out second))
        {
            addSecond(item, second);
        }

请注意，我添加了var ctr = 0; var mapped2 = conn.QueryMultiple(query, new {id}) .Map<Student, Enrollment, Course, int>( student => student.StudentId, enrollment => ctr = enrollment.StudentId, course=>course.CourseId = ctr, ((student, enrollments) => { student.Enrollments = enrollments; }), ((student, courses) => courses.ToList().ForEach(s=> student.Enrollments.ToList().ForEach(x=>x.Course = new Course { Title = s.Title }))));以获取ctr中CourseId的值。好了，我现在面临另一个问题，如何获得enrollment => ctr = enrollment.StudentId的值这是我的代码

（（学生，课程）=＆gt; courses.ToList（）。ForEach（s =＆gt; student.Enrollments.ToList（）。ForEach（x =＆gt; x.Course = new Course { Title = s.Title }））

我只获得最后一个值

Answer 1

以下是我解决问题的方法

如上面的更新2 详细信息，我添加了一个变量ctr，以便从CourseId获取Enrollment的值并传递给Course得到正确的价值。在那之后，我面临另一个问题，如何从Course Student.Enrollment.Course传递var enrollLst = new List<Enrollment>();的值，这是我如何理解的。

我创建了一个变量Enrollment来保存第一个动作中((student, enrollments) => { enrollLst = enrollments.ToList(); }),的值

((student, courses) =>
                {
                    var ctrId = 0;  
                    courses.ToList().ForEach(cour =>
                    {
                        if (cour != null)
                        {
                            enrollLst[ctrId].Course = cour;
                            ctrId++;
                        }
                        else
                        {
                            enrollLst[ctrId].Course = null;
                            ctrId++;
                        }   
                    });
                    student.Enrollments = enrollLst;
                })).FirstOrDefault();

第二行动

_connection = Connect.GetOpenConnection();
        const string query = "SELECT * from Student stu where StudentId = @id  " +
                             "SELECT * from Enrollment enr where enr.StudentId in ( SELECT StudentId from Student stu where Studentid = @id)  " +
                             "SELECT * FROM Course cou WHERE cou.CourseId in (SELECT CourseId from Enrollment where StudentId = @id)";

        var enrollLst = new List<Enrollment>();
        var ctr = 0;
        var result = _connection.QueryMultiple(query, new { id })
            .Map<Student, Enrollment, Course, int>(
                student => student.StudentId,
                enrollment => ctr = enrollment.StudentId,
                course => course.CourseId = ctr,
                ((student, enrollments) =>
                {
                    enrollLst = enrollments.ToList();
                }),
                ((student, courses) =>
                {
                    var ctrId = 0;  
                    courses.ToList().ForEach(cour =>
                    {
                        if (cour != null)
                        {
                            enrollLst[ctrId].Course = cour;
                            ctrId++;
                        }
                        else
                        {
                            enrollLst[ctrId].Course = null;
                            ctrId++;
                        }   
                    });
                    student.Enrollments = enrollLst;
                })).FirstOrDefault();

下面是我的整个代码

public static IEnumerable<TFirst> Map<TFirst, TSecond, TThird, TKey>
        (
        this SqlMapper.GridReader reader,
        Func<TFirst, TKey> firstKey,
        Func<TSecond, TKey> secondKey,
        Func<TThird, TKey> thirdKey,
        Action<TFirst, IEnumerable<TSecond>> addSecond,
        Action<TFirst, IEnumerable<TThird>> addThird
        )
    {
        var result = reader.Read<TFirst>().ToList();

        var secondMap = reader
            .Read<TSecond>()
            .GroupBy(secondKey)
            .ToDictionary(g => g.Key, g => g.AsEnumerable());

        var thirdMap = reader
           .Read<TThird>()
           .GroupBy(thirdKey)
           .ToDictionary(g => g.Key, g => g.AsEnumerable());     

        foreach (var item in result)
        {
            IEnumerable<TSecond> second;
            if (secondMap.TryGetValue(firstKey(item), out second))
            {
                addSecond(item, second);
            }

            IEnumerable<TThird> third;
            if (thirdMap.TryGetValue(firstKey(item), out third))
            {
                addThird(item, third);
            }  
        }  
        return result.ToList();
    }

带有映射器的GridReader，按照指示here

扩展了3级层次结构

{{1}}

Multi-Mapper在Dapper中的一对多关系

1 个答案: