Question

I have two different collections like below

public class Student
{
    public int StudentID { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }      
}

public class Skills
{
    public int SkillID { get; set; }
    public int StudentID { get; set; }
    public string Keyskill_Name { get; set; }        
    public int LastUsedYear { get; set; }
}

Here one student can contain multiple keyskils

I just want to fill a new collection like below

public class StudentDetails
{
    public int StudentID { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public list<string> Keyskill_Name { get; set; }
}

Please help me. Thanks in advance.

Answer 1

The GroupJoin LINQ method is the perfect solution for this case:

    List<Student> students = new List<Student>();
    List<Skills> skills = new List<Skills>();

    List<StudentDetails> studentDetails = students.GroupJoin(skills, student => student.StudentID, skill => skill.StudentID, (student, skillsForStudent) => new StudentDetails
    {
        FirstName = student.FirstName,
        LastName = student.LastName,
        StudentID = student.StudentID,
        Keyskill_Name = (from skill in skillsForStudent
                         select skill.Keyskill_Name).ToList()
    }).ToList();

How to use the GroupJoin method?

• Call the method from the set that gives a 1 to 1 relation with the result (Here for each Student, there is one and only one corresponding StudentDetails.
• The first argument of the method is the set you want to “distribute” on the other items (Here the skills are “distributed” over the entire set of students)
• The second and third arguments are used to explain how to make the collision between the elements of the first set and the elements of the second set. Lambda expressions are extremely useful in this case.
• Lastly, the fourth argument, is used to define the result. It is a function with 2 parameters : an element of the first set (here students) and its corresponding elements in the second set that have been found using the collision.