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我正在尝试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

[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; }
    }

注册

[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; }
    }

课程

[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; }
}

这是我的简洁代码

_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();

按照指令在这里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

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();
    }

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价值。我希望你能帮助我谢谢。 失败的

更新 1

我注意到我在这里得到了空值，它没有进入 if 语句

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

更新 2

我在这里解决问题就是我所做的

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
                }))));

请注意，我添加ctr以获取CourseIdin的值enrollment => ctr = enrollment.StudentId。好的，现在我面临另一个问题，如何获得courses 这里的值是我的代码

（（学生，课程）=> courses.ToList().ForEach(s=> student.Enrollments.ToList().ForEach(x=>x.Course = new Course { Title = s.Title }))

我只得到最后一个值

4

1 回答 1

0

这是我解决问题的方法

正如上面的UPDATE 2详细信息，我添加了一个变量ctr来获取CourseIdfrom的值Enrollment并传递给以Course获取正确的值。Course之后，我面临另一个问题，如何从这里传递值，Student.Enrollment.Course这就是我如何计算出来的。

我创建一个变量var enrollLst = new List<Enrollment>();来保存Enrollment第一个动作的值

((student, enrollments) =>
                {
                    enrollLst = enrollments.ToList();
                }),

第二次行动

((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

_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();

按照此处的说明，带有映射器的 GridReader 扩展了 3 级层次结构

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();
    }
于 2015-09-02T07:30:17.863 回答