问题
I am trying to get the value of my database with a relation one to many i have my object like this
Student
[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; }
}
Enrollment
[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; }
}
Course
[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; }
}
Here is my dapper code
_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();
as per instruction Here All i have to do is to extend 3 level hierarchy but i cant make it work
here is my GridReader with mapper
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();
}
when i run my app here is the result with the id of 1 notice that the Course title have no value. i hope you can help me thank you.
UPDATE 1
I notice that i am getting the null value here, it doesnt get inside the if statement
IEnumerable<TSecond> second;
if (secondMap.TryGetValue(firstKey(item), out second))
{
addSecond(item, second);
}
UPDATE 2
I solve the problem here is what i do
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
}))));
notice that i added ctr to get the value of CourseId in enrollment => ctr = enrollment.StudentId.
Ok now I face another problem, how to get the value of courses
here is my code
((student, courses) => courses.ToList().ForEach(s=> student.Enrollments.ToList().ForEach(x=>x.Course = new Course { Title = s.Title }))
i am only getting the last value
回答1:
Here is how i solve my problem
As the above UPDATE 2 details i added a variable ctr to get the value of CourseId from Enrollment and pass to Course to get the right value. After that i face another problem how to pass the value of Course from Student.Enrollment.Course here's how i figure it out.
I create a variable var enrollLst = new List<Enrollment>(); to hold the value of Enrollment from the first action
((student, enrollments) =>
{
enrollLst = enrollments.ToList();
}),
Second Action
((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();
below is my whole code
_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();
GridReader with mapper extended with 3 level hierarchy as instructed here
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();
}
来源：https://stackoverflow.com/questions/32305090/multi-mapper-in-dapper-one-to-many-relations