a類的屬性指的是同一個類。如何管理實例

Question

我的模塊中有以下代碼：

Class Studentdatabase
{
public List <student> studentslist;
public void UpdateStudentDetailsinlist();
}


Class student
{
public string name;
public int age;
public int marks;
public student friend;
}

我的模塊使用數據填充此數據庫，此數據庫將由另一個模塊使用。

studentslist [0]
name - Trevor
age -12
marks - 33
friend - 
    name - Sam
    age - 12
    marks - 45

studentslist [1]
name - Warren
age -13
marks - 63
friend - 
    name - Sam
    age - 12
    marks - 45

studentslist [2]
name - Sam
age -12
marks - 45
friend - null

我的要求是，如果學生列表[2]（Sam）的標記更新為48，則必須自動更新學生列表[0]和學生列表[1]中的Sam標記（反向）。 如何在模塊中實現？

Answer 1

好吧，首先你需要一個標識符（某種類型 - Guid，int等），這將是你的主鍵。

需要保存在數據庫中的實際值是朋友的標識符。

Class student
{
   public int id;
   public string name;
   public int age;
   public int marks;
   public int StudentFriendId;
}

Answer 2

您可以使用如下。

class StudentContext
{
    public List<Student> Studentslist { get; set; }

    public void AddStudent(Student student)
    {
        if (null == Studentslist)
        {
            Studentslist = new List<Student>();
        }
        Studentslist.Add(student);
    }

    public void AddFriend(Student student,Student friendStudent)
    {
        Studentslist.Where(x => x.StudentId == student.StudentId).FirstOrDefault().Friend = friendStudent;
    }
}

class Student
{
    public int StudentId { get; set; }
    public string Name { get; set; }
    public int Age { get; set; }
    public int Marks { get; set; }
    public Student Friend { get; set; }
}

public class Test
{
    public static void Main()
    {
        Student student1 = new Student();
        student1.StudentId = 1;
        student1.Name = "A";
        student1.Marks = 100;

        Student student2 = new Student();
        student2.StudentId = 2;
        student2.Name = "AB";
        student2.Marks = 10;

        StudentContext studentContext = new StudentContext();
        studentContext.AddStudent(student1);
        studentContext.AddStudent(student2);
        studentContext.AddFriend(student1, student2);

        student1.Marks = 50;
        student2.Marks = 77;
    }
}

Answer 3

您應該使用相同的參考，它將反映在所有地方。

例：

Student sam = new Student();
sam.Marks = 45;
//... other sam properties


Student warren = new Student();
// initialize all waren properties
waren.friend = sam;

// do same for trevor
Student trevor = new Student();


List<Student> students = new List<Student>();
students.Add(sam);
students.Add(waren);
students.Add(trevor);

//Now waren/trevor holds same student reference which is in student list so any change in sam will be reflected in friend of waren/trevor
sam.Marks = 48;// reflected at all 3 places.

如果要更改行為，可以將Student更改為struct（從類中）或將sam的copy / clone分配給waren / trevor的朋友

Answer 4

你應該遵循以下結構，並在朋友中放入id而不是整個instnce

Class Studentdatabase
{
  public List <student> studentslist;
  public void UpdateStudentDetailsinlist();
}


   Class student
   {
      public int id,
      public string name;
      public int age;
      public int marks;
      public int friend; // it will contain id of that friend in student
   }

Answer 5

首先，唯一的標識符是必須的，類似於整數id字段。 如果Name屬性足夠好，那就行了，但這通常不是一個好主意（這意味着只有一個學生可以有一個特定的名字）。 一些選擇：

1. 正如Tilak所說，更新相同的參考資料。

2. 如果您無法確定這一點，一個想法是強制在每個唯一學生（id）的應用程序中維護單個引用。

    class Student { //ideally properties public int id public string name; public int age; public int marks; public Student friend; static readonly Dictionary<int, Student> students = new Dictionary<int, Student>(); //a static factory method with whatever definition, but int id is a must public static Student Create(int id, string name, int age, int marks) { Student student; return students.TryGetValue(id, out student) ? student : new Student(id, name, age, marks) } //private constructor, with whatever definition. private Student(int id, string name, int age, int marks) { } } 

   覆蓋Equals和GetHashCode賦予它更好的意義。

3. 如果上面的內存太多並且更新直接發生在數據庫中，則可以避免Student類上的屬性/字段friend ，但提供了一種從db進行查詢的方法。 就像是：

    class Student { //ideally properties public int id public string name; public int age; public int marks; private int friendId; //private it is public Student GetFriend() { return db.GetStudent(friendId); } }