C# 从列表中查找数据

Question

我有一个教师列表，我希望能够显示特定教师列表中的所有数据。我想按名字搜索。但是，要么我的列表为空，要么我无法从中获取数据。我不知道问题出在哪里。

这是我如何将数据从我的 sql server 数据库加载到我的列表中：

    public void connectDbRead(List<Teacher> Teachers)
    {
        var teacherData = TeacherData.GetInstance();
        //Get all students in the singleton
        var teachers = teacherData.Teachers;

        using (SqlConnection conn = new SqlConnection())
        {               
            conn.ConnectionString = "Server=DESKTOP;Database=Test;Trusted_Connection=true";
            conn.Open();

            SqlCommand command = new SqlCommand("SELECT * FROM TEACHERS", conn);
            command.Parameters.Add(new SqlParameter("0", 1));

            teachers.Clear();
            using (SqlDataReader reader = command.ExecuteReader())
            {                   
                while (reader.Read())
                {
                    teachers.Add(new Teacher
                    {
                        Name = (string)reader["NAME"],
                        FamilyName = (string)reader["FAMILY_NAME"],
                        Age = (int)reader["AGE"]                           
                    });

                    Console.WriteLine(String.Format("{0} | {1}| {2}",
                        reader[1], reader[2], reader[3]));
                }
            }              
        }
    }

这是我从列表中搜索数据的方式：

    public void searchTeacher(List<Teacher> Teachers)
    {       
        string teacherName = "";
        Console.WriteLine("Who do you want to find. Write his name: ");
        teacherName = Console.ReadLine();

        List<Teacher> teachers = Teachers.FindAll(x => x.Name == teacherName);

        Console.WriteLine("List Of ELements!");
        foreach (Teacher t in teachers)
        {
            Console.WriteLine(t.ToString());
        }
   }

我在 main 函数中这样调用它，但在 switch 情况下：

        var teacherData = TeacherData.GetInstance();
        var teachers = teacherData.Teachers;                
        teacherData.searchTeacher(teachers);                     
        teacherData.connectDbRead(teachers);

Answer 1

一条线解决方案（甚至不需要使用LINQ）：

foreach(teachers t in Teacher)

  if (t.Name == "TeacherName or any searcj query")

    MessageBox.Show(t.name & t.age & .......)

或者，如果您仍想使用 LINQ：

 forech(Teachers t in Teacher)

  var result = Teachers.Where(Teacher => t.Name == "Name Here")

 /// use the result as u want )

Answer 2

我改变了一些东西；删除了一些我看不懂的东西，但是我用这种方式测试过，它确实有效。

class Program
    {
        static List<Teacher> teachers = new List<Teacher>();
        static void Main(string[] args)
        {
            connectDbRead();
            searchTeacher();
            Console.ReadLine();
        }
        public static void connectDbRead()
        {
            using (SqlConnection conn = new SqlConnection("Server=DESKTOP;Database=Test;Trusted_Connection=true"))
            {
                conn.Open();
                SqlCommand command = new SqlCommand("SELECT * FROM TEACHERS", conn);

                teachers.Clear();
                using (SqlDataReader reader = command.ExecuteReader())
                {
                    while (reader.Read())
                    {
                        teachers.Add(new Teacher
                        {
                            Name = (string)reader["NAME"],
                            FamilyName = (string)reader["FAMILY_NAME"],
                            Age = (int)reader["AGE"]
                        });
                    }
                }
            }
        }
        public static void searchTeacher()
        {
            string teacherName = "";
            Console.WriteLine("Who do you want to find. Write his name: ");
            teacherName = Console.ReadLine();

            var foundTeachers = teachers.FindAll(x => x.Name == teacherName);

            Console.WriteLine("List Of ELements!");
            foreach (Teacher t in foundTeachers)
            {
                Console.WriteLine(String.Format("{0} | {1} | {2}", t.Name, t.FamilyName, t.Age));
            }
        }
    }
    public class Teacher
    {
        public int Age { get; set; }
        public string Name { get; set; }
        public string FamilyName  { get; set; }
    }