在 C# 中使用列表 - 不使用数据库 - 多对多

Question

我已经看过How to model a Many to many-relationship in code?

我不太明白答案。

也看过C# Mapping Many To Many，但不想使用实体框架/数据库

我有学生和科目

public class Subject : Student
    {
        public string SubjectName { get; set; }
        public string StudentClassNumber { get; set; }
    }

    public class Student
    {
        public string StudentName { get; set; }
        public string isjoined { get; set; }


    }

然后实例化

List<Subject> subject = new List<Subject>();

并添加值/属性

subject2.Add(new Subject2() { SubjectName = "Math", StudentName = "Ben", isjoined = "yes", StudentClassNumber ="2" });
            subject2.Add(new Subject2() { SubjectName = "Math", StudentName2 = "Andrew", isjoined = "yes", StudentClassNumber = "4" });
            subject2.Add(new Subject2() { SubjectName = "Science", StudentName2 = "Andrew", isjoined = "no", StudentClassNumber = "5" });
            subject2.Add(new Subject2() { SubjectName = "Science", StudentName2 = "Ben", isjoined = "no", StudentClassNumber = "3" });

现在我的问题是，“数学”中的“安德鲁”或“本”与“科学”中的（学生）相同，这不是新的安德鲁和本

我想有一个 WriteLine 写：Math - StudentName - StudentClassNumber - 已加入， 两个/所有学生

即数学： 本 2 是的 安德鲁 4 是的

科学 本 3 没有 安德鲁 4 没有

这是使用 linq 的尝试

class Students
    {
        public string StudentName { get; set; }

    }

    class Subject
    {
        public string Name { get; set; }
        public Students Occupier { get; set; }
    }

    class InnerJoin3
    {
        public static void DoJoin()
        {
            Students ben = new Students { StudentName = "Ben" };
            Students andrew = new Students { StudentName = "Andrew" };


            Subject math = new Subject { Name = "Math", Occupier = andrew };
            Subject science = new Subject { Name = "Science", Occupier = ben };

            // Create two lists.
            List<Students> people = new List<Students> { ben, andrew };
            List<Subject> subjects = new List<Subject> { math, science };

            // Create a collection of student-subject pairs. Each element in the collection
            // is an anonymous type containing both the student's name and their subject's name.
            var query = from student in people
                        join subject in subjects on student equals subject.Occupier
                        select new { OccupierName = student.StudentName, SubjectName = subject.Name };

            foreach (var ownerAndSubject in query)
            {
                Console.WriteLine($"\"{ownerAndSubject.SubjectName}\" is the subject of choice for {ownerAndSubject.OccupierName}");
            }
        }
    }

Answer 1

好吧，如果它像你说的那样。您希望在控制台应用程序中获得以下结果：

Math: name, name
Science: name.. etc.

在您的主类中添加以下内容：

static void Main(string[] args)
        {
            Students ben = new Students { StudentName = "Ben" };
            Students andrew = new Students { StudentName = "Andrew" };


            Subject mathAndrew = new Subject { Name = "Math", Students = andrew };
            Subject ScienceAndrew = new Subject { Name = "Science", Students = andrew };
            Subject scienceBen = new Subject { Name = "Science", Students = ben };

            List<Students> people = new List<Students> { ben, andrew };
            List<Subject> subjects = new List<Subject> { mathAndrew, ScienceAndrew, scienceBen };

            var query = from student in people
                        join subject in subjects on student equals subject.Students
                        select new SetQuery(student.StudentName, subject.Name);

            ScienceResult(query);
        }

并添加此方法：

注意，为了创建 ScienceResult 方法，我们需要一个 SetQuery 类实例。

public static void ScienceResult(IEnumerable<SetQuery> query)
        {
            Console.Write("Science: ");
            foreach (var result in query)
            {
                if (result.Name == "Science")
                {
                    Console.Write(result.StudentName + " ");
                }
            }

            Console.WriteLine();

            Console.Write("Math: ");
            foreach (var result in query)
            {
                if (result.Name == "Math")
                {
                    Console.Write(result.StudentName + " ");
                }
            }

            Console.WriteLine();
        }

使用依赖注入设置查询类实例

internal class SetQuery
    {
        public string StudentName;
        public string Name;

        public SetQuery(string studentName, string name)
        {
            this.StudentName = studentName;
            this.Name = name;
        }
    }

结果是：

Science: Ben Andrew
Math: Andrew

对于最佳实践，我会使用数据库来保存您的信息并GET您的信息来自。此外，方法 ScienceResult 是 NOT DRY 你想要改变。这仅用于说明目的。

有关 DRY 的更多信息，请查看以下内容： DRY (Don't Repeat Yourself) and if assignements

Answer 2

不确定您到底在寻找什么，但最好的软件实践是该死的，给您（假设解决方案称为“stackoverflow61918396”）：

Student.cs

using System.Collections.Generic;

namespace stackoverflow61918396
{
    class Student
    {
        public string Id { get; set; }

        public string Name { get; set; }

        public List<string> SubjectsEnrolledIn { get; set; }

        public Student()
        {
            SubjectsEnrolledIn = new List<string>();
        }
    }
}

Subject.cs

using System.Collections.Generic;

namespace stackoverflow61918396
{
    class Subject
    {
        public string Id { get; set; }

        public int ClassNumber { get; set; }

        public string Name { get; set; }

        public List<string> StudentsInSubject { get; set; }

        public Subject()
        {
            StudentsInSubject = new List<string>();
        }
    }
}

Manager.cs

using System;
using System.Collections.Generic;
using System.Linq;

namespace stackoverflow61918396
{
    class Manager
    {
        public static List<Student> Students { get; set; }

        public static List<Subject> Subjects { get; set; }

        public Manager()
        {
            Students = new List<Student>();
            Subjects = new List<Subject>();

            // Seed some students
            var ben = new Student() { Id = Guid.NewGuid().ToString(), Name = "Ben" };
            var andrew = new Student() { Id = Guid.NewGuid().ToString(), Name = "Andrew" };
            var amanda = new Student() { Id = Guid.NewGuid().ToString(), Name = "Amanda" };
            var greg = new Student() { Id = Guid.NewGuid().ToString(), Name = "Greg" };
            var peter = new Student() { Id = Guid.NewGuid().ToString(), Name = "Peter" };
            var jessica = new Student() { Id = Guid.NewGuid().ToString(), Name = "Jessica" };
            var james = new Student() { Id = Guid.NewGuid().ToString(), Name = "James" };
            var doug = new Student() { Id = Guid.NewGuid().ToString(), Name = "Doug" };
            var cory = new Student() { Id = Guid.NewGuid().ToString(), Name = "Cory" };
            var laura = new Student() { Id = Guid.NewGuid().ToString(), Name = "Laura" };
            Students.Add(ben);
            Students.Add(andrew);
            Students.Add(amanda);
            Students.Add(greg);
            Students.Add(peter);
            Students.Add(jessica);
            Students.Add(james);
            Students.Add(doug);
            Students.Add(cory);
            Students.Add(laura);

            // Seed a couple sections of math and science
            var math2 = new Subject() { Id = Guid.NewGuid().ToString(), Name = "Math", ClassNumber = 2 };
            var math4 = new Subject() { Id = Guid.NewGuid().ToString(), Name = "Math", ClassNumber = 4 };
            var science5 = new Subject() { Id = Guid.NewGuid().ToString(), Name = "Science", ClassNumber = 5 };
            var science3 = new Subject() { Id = Guid.NewGuid().ToString(), Name = "Science", ClassNumber = 3 };
            Subjects.Add(math2);
            Subjects.Add(math4);
            Subjects.Add(science5);
            Subjects.Add(science3);

            // Seed some enrollments
            Enroll(ben.Id, math2.Id);
            Enroll(andrew.Id, math2.Id);
            Enroll(andrew.Id, science5.Id);
            Enroll(amanda.Id, math2.Id);
            Enroll(peter.Id, math2.Id);
            Enroll(jessica.Id, math4.Id);
            Enroll(james.Id, math2.Id);
            Enroll(doug.Id, math4.Id);
            Enroll(doug.Id, science5.Id);
        }

        public Student AddStudent(string name)
        {
            var student = new Student() { Id = Guid.NewGuid().ToString(), Name = name };
            Students.Add(student);

            return student;
        }

        public Subject AddSubject(string name, int classNumber)
        {
            var subject = new Subject() { Id = Guid.NewGuid().ToString(), Name = name, ClassNumber = classNumber };
            Subjects.Add(subject);

            return subject;
        }

        public bool DeleteStudent(string id)
        {
            try
            {
                var student = Students.Where(s => s.Id == id).FirstOrDefault();

                if (student == null) return false;

                Students.Remove(student);

                return true;
            }
            catch (Exception)
            {
                return false;
            }
        }

        public bool DeleteSubject(string id)
        {
            try
            {
                var subject = Subjects.Where(s => s.Id == id).FirstOrDefault();

                if (subject == null) return false;

                Subjects.Remove(subject);

                return true;
            }
            catch (Exception)
            {
                return false;
            }
        }

        public bool Disenroll(string studentId, string subjectId)
        {
            var student = Students.Where(s => s.Id == studentId).First();
            var subject = Subjects.Where(s => s.Id == subjectId).First();

            try
            {
                student.SubjectsEnrolledIn.Remove(subjectId);
                subject.StudentsInSubject.Remove(studentId);
            }
            catch (Exception)
            {
                return false;
            }

            return true;
        }

        public Student EditStudent(string id, string name)
        {
            var student = Students.Where(s => s.Id == id).FirstOrDefault();

            if (student == null) return null;

            student.Name = name;

            return student;
        }

        public Subject EditSubject(string id, string name, int classNumber)
        {
            var subject = Subjects.Where(s => s.Id == id).FirstOrDefault();

            if (subject == null) return null;

            subject.Name = name;
            subject.ClassNumber = classNumber;

            return subject;
        }

        public bool Enroll(string studentId, string subjectId)
        {
            var student = Students.Where(s => s.Id == studentId).First();
            var subject = Subjects.Where(s => s.Id == subjectId).First();

            try
            {
                student.SubjectsEnrolledIn.Add(subjectId);
                subject.StudentsInSubject.Add(studentId);
            }
            catch (Exception)
            {
                return false;
            }

            return true;
        }

        public Student GetStudent(string id)
        {
            return Students.Where(s => s.Id == id).FirstOrDefault();
        }

        public Subject GetSubject(string id)
        {
            return Subjects.Where(s => s.Id == id).FirstOrDefault();
        }

        public IEnumerable<IGrouping<string, Tuple<string, int, string>>> GetSubjectAllStudents(string id)
        {
            var tupleList = new List<Tuple<string, int, string>>();

            var subjectName = Subjects.Where(s => s.Id == id).FirstOrDefault()?.Name;
            var subjectList = Subjects.Where(s => s.Name == subjectName).ToList();

            if (subjectName == null) return null;

            foreach (Subject subject in subjectList)
            {
                foreach (Student student in Students)
                {
                    if (subject.StudentsInSubject.Contains(student.Id))
                    {
                        tupleList.Add(new Tuple<string, int, string>(student.Name, subject.ClassNumber, "yes"));
                    }
                    else
                    {
                        tupleList.Add(new Tuple<string, int, string>(student.Name, subject.ClassNumber, "no"));
                    }
                }
            }

            var sortedTupleList = tupleList.GroupBy(x => x.Item1);

            return sortedTupleList;
        }

        public List<Subject> GetSubjectAlternatives(string id)
        {
            var subjectName = Subjects.Where(s => s.Id == id).FirstOrDefault()?.Name;

            if (subjectName == null) return null;

            return Subjects.Where(s => s.Name == subjectName).ToList();
        }

        public List<Student> ListStudents()
        {
            return Students;
        }

        public List<Subject> ListSubjects()
        {
            return Subjects;
        }
    }
}

Program.cs

using System;
using System.Collections.Generic;

namespace stackoverflow61918396
{
    class Program
    {
        static bool Again { get; set; }
        static Manager Manager { get; set; }

        static void Main()
        {            
            Again = true;
            Manager = new Manager();

            do
            {
                Console.WriteLine("Enter a command (type 'help' for options):");
                var selection = Console.ReadLine();
                Console.WriteLine("\n");

                CommandHandler(selection);
            } while (Again);
        }

        static void CommandHandler(string command)
        {
            switch (command)
            {
                case var s when s.Trim().ToLower() == "help":
                    Console.WriteLine("Commands:");
                    Console.WriteLine("'quit' - exits the program");
                    Console.WriteLine("'students' - lists all students");
                    Console.WriteLine("'subjects' - lists all subjects");                    
                    Console.WriteLine("'student [id]' - shows this student's record");
                    Console.WriteLine("'subject [id]' - shows this subject's record");
                    Console.WriteLine("'all students by subject [id]' - lists all students in this subject or not");
                    Console.WriteLine("'alternatives for subject [id]' - lists all class numbers of a subject");
                    Console.WriteLine("'new student [name]' - adds a new student");
                    Console.WriteLine("'new subject [name] [class number]' - adds a new subject");
                    Console.WriteLine("'edit student [id] [name]' - edits an existing student");
                    Console.WriteLine("'edit subject [id] [name] [class number]' - edits an existing subject");
                    Console.WriteLine("'delete student [id]' - deletes an existing student");
                    Console.WriteLine("'delete subject [id]' - deletes an existing subject");
                    Console.WriteLine("'enroll [student id] [subject id]' - enrolls a student into a subject");
                    Console.WriteLine("'disenroll [student id] [subject id]' - disenrolls a student from a subject");
                    Console.WriteLine("\n");
                    break;
                case var s when s.Trim().ToLower() == "quit":
                    Again = false;
                    break;
                case var s when s.Trim().ToLower() == "students":
                    try
                    {
                        List<Student> studentList = Manager.ListStudents();

                        if (studentList == null) throw new Exception();

                        Console.WriteLine("Students:");
                        foreach (Student student in studentList)
                        {
                            Console.WriteLine("Id: " + student.Id + ", Name: " + student.Name);
                        }
                        Console.WriteLine("\n");
                    }
                    catch (Exception)
                    {
                        Console.WriteLine("Unrecognized command. Please try again.");
                        Console.WriteLine("\n");
                    }
                    break;
                case var s when s.Trim().ToLower() == "subjects":
                    try
                    {
                        List<Subject> subjectList = Manager.ListSubjects();

                        if (subjectList == null) throw new Exception();

                        Console.WriteLine("Subjects:");
                        foreach (Subject subject in subjectList)
                        {
                            Console.WriteLine(
                                "Id: " + subject.Id +
                                ", Class Number: " + subject.ClassNumber +
                                ", Name: " + subject.Name
                            );
                        }
                        Console.WriteLine("\n");
                    }
                    catch (Exception)
                    {
                        Console.WriteLine("Unrecognized command. Please try again.");
                        Console.WriteLine("\n");
                    }
                    break;
                case var s when s.Trim().ToLower().StartsWith("student"):
                    try
                    {
                        var studentId = s.Split(' ')[1];
                        var student = Manager.GetStudent(studentId);

                        if (student == null) throw new Exception();

                        Console.WriteLine("Id: " + student.Id + ", Name: " + student.Name);

                        Console.WriteLine("Subjects Enrolled In:");
                        foreach (string subjectId in student.SubjectsEnrolledIn)
                        {
                            var subject = Manager.GetSubject(subjectId);
                            Console.WriteLine(
                                "Id: " + subject.Id + 
                                ", Class Number: " + subject.ClassNumber + 
                                ", Name: " + subject.Name
                            );
                        }
                        Console.WriteLine("\n");
                    }
                    catch (Exception)
                    {
                        Console.WriteLine("Unrecognized command. Please try again.");
                        Console.WriteLine("\n");
                    }
                    break;
                case var s when s.Trim().ToLower().StartsWith("subject"):
                    try
                    {
                        var subjectId = s.Split(' ')[1];
                        var subject = Manager.GetSubject(subjectId);

                        if (subject == null) throw new Exception();

                        Console.WriteLine("Id: " + subject.Id + ", Name: " + subject.Name);

                        Console.WriteLine("Students In Subject:");
                        foreach (string studentId in subject.StudentsInSubject)
                        {
                            var student = Manager.GetStudent(studentId);
                            Console.WriteLine(
                                "Id: " + student.Id +
                                ", Name: " + student.Name
                            );
                        }
                        Console.WriteLine("\n");
                    }
                    catch (Exception)
                    {
                        Console.WriteLine("Unrecognized command. Please try again.");
                        Console.WriteLine("\n");
                    }
                    break;
                case var s when s.Trim().ToLower().StartsWith("all"):
                    try
                    {
                        var subjectId = s.Split(' ')[4];
                        var subjectName = Manager.GetSubject(subjectId)?.Name;
                        var subjectWithAll = Manager.GetSubjectAllStudents(subjectId);

                        if (subjectWithAll == null) throw new Exception();

                        Console.WriteLine("All students with respect to " + (subjectName ?? subjectId) + ":");
                        foreach (var group in subjectWithAll)
                        {
                            foreach (var item in group)
                            {
                                Console.WriteLine(
                                    "\tName: " + item.Item1 +
                                    ", \t\tClass Number: " + item.Item2 +
                                    ", \t\tEnrolled: " + item.Item3
                                );
                            }
                        }
                        Console.WriteLine("\n");
                    }
                    catch (Exception)
                    {
                        Console.WriteLine("Unrecognized command. Please try again.");
                        Console.WriteLine("\n");
                    }
                    break;
                case var s when s.Trim().ToLower().StartsWith("alternatives"):
                    try
                    {
                        var subjectId = s.Split(' ')[3];
                        List<Subject> subjectAlternatives = Manager.GetSubjectAlternatives(subjectId);

                        if (subjectAlternatives == null) throw new Exception();

                        Console.WriteLine("Alternatives for " + subjectAlternatives[0].Name + ":");
                        foreach (Subject subject in subjectAlternatives)
                        {
                            Console.WriteLine("Id: " + subject.Id + ", Class Number: " + subject.ClassNumber);
                        }
                        Console.WriteLine("\n");
                    }
                    catch (Exception)
                    {
                        Console.WriteLine("Unrecognized command. Please try again.");
                        Console.WriteLine("\n");
                    }
                    break;
                case var s when s.Trim().ToLower().StartsWith("new student"):
                    try
                    {
                        var name = s.Split(' ')[2];
                        var student = Manager.AddStudent(name);

                        if (student == null) throw new Exception();

                        Console.WriteLine("Student " + student.Id + " created");
                        Console.WriteLine("\n");
                    }
                    catch (Exception)
                    {
                        Console.WriteLine("Unrecognized command. Please try again.");
                        Console.WriteLine("\n");
                    }
                    break;
                case var s when s.Trim().ToLower().StartsWith("new subject"):
                    try
                    {
                        var name = s.Split(' ')[2];
                        var classNumber = s.Split(' ')[3];
                        var subject = Manager.AddSubject(name, int.Parse(classNumber));

                        if (subject == null) throw new Exception();

                        Console.WriteLine("Subject " + subject.Id + " created");
                        Console.WriteLine("\n");
                    }
                    catch (Exception)
                    {
                        Console.WriteLine("Unrecognized command. Please try again.");
                        Console.WriteLine("\n");
                    }
                    break;
                case var s when s.Trim().ToLower().StartsWith("edit student"):
                    try
                    {
                        var studentId = s.Split(' ')[2];
                        var studentName = s.Split(' ')[3];
                        var student = Manager.EditStudent(studentId, studentName);

                        if (student == null) throw new Exception();

                        Console.WriteLine("Student " + student.Id + " was edited");
                        Console.WriteLine("\n");
                    }
                    catch (Exception)
                    {
                        Console.WriteLine("Unrecognized command. Please try again.");
                        Console.WriteLine("\n");
                    }
                    break;
                case var s when s.Trim().ToLower().StartsWith("edit subject"):
                    try
                    {
                        var subjectId = s.Split(' ')[2];
                        var subjectName = s.Split(' ')[3];
                        var subjectClassNumber = s.Split(' ')[4];
                        var subject = Manager.EditSubject(subjectId, subjectName, int.Parse(subjectClassNumber));

                        if (subject == null) throw new Exception();

                        Console.WriteLine("Subect " + subject.Id + " was edited");
                        Console.WriteLine("\n");
                    }
                    catch (Exception)
                    {
                        Console.WriteLine("Unrecognized command. Please try again.");
                        Console.WriteLine("\n");
                    }
                    break;
                case var s when s.Trim().ToLower().StartsWith("delete student"):
                    try
                    {
                        var studentId = s.Split(' ')[2];
                        var deleted = Manager.DeleteStudent(studentId);

                        Console.WriteLine("Student was " + (deleted ? "" : "not") + " deleted");
                        Console.WriteLine("\n");
                    }
                    catch (Exception)
                    {
                        Console.WriteLine("Unrecognized command. Please try again.");
                        Console.WriteLine("\n");
                    }
                    break;
                case var s when s.Trim().ToLower().StartsWith("delete subject"):
                    try
                    {
                        var subjectId = s.Split(' ')[2];
                        var deleted = Manager.DeleteSubject(subjectId);

                        Console.WriteLine("Subject was " + (deleted ? "" : "not") + " deleted");
                        Console.WriteLine("\n");
                    }
                    catch (Exception)
                    {
                        Console.WriteLine("Unrecognized command. Please try again.");
                        Console.WriteLine("\n");
                    }
                    break;
                case var s when s.Trim().ToLower().StartsWith("enroll"):
                    try
                    {
                        var studentId = s.Split(' ')[1];
                        var subjectId = s.Split(' ')[2];
                        var enrolled = Manager.Enroll(studentId, subjectId);

                        Console.WriteLine("Student was " + (enrolled ? "" : "not") + " enrolled");
                        Console.WriteLine("\n");
                    }
                    catch (Exception)
                    {
                        Console.WriteLine("Unrecognized command. Please try again.");
                        Console.WriteLine("\n");
                    }
                    break;
                case var s when s.Trim().ToLower().StartsWith("disenroll"):
                    try
                    {
                        var studentId = s.Split(' ')[1];
                        var subjectId = s.Split(' ')[2];
                        var disenrolled = Manager.Disenroll(studentId, subjectId);

                        Console.WriteLine("Student was " + (disenrolled ? "" : "not") + " disenrolled");
                        Console.WriteLine("\n");
                    }
                    catch (Exception)
                    {
                        Console.WriteLine("Unrecognized command. Please try again.");
                        Console.WriteLine("\n");
                    }
                    break;
                default:
                    Console.WriteLine("Unrecognized command. Please try again.");
                    Console.WriteLine("\n");
                    break;
            }
        }
    }
}