没有实体框架的MVC3多对多

Question

I'm creating a MVC3 sample project instead of Entity Framework. I created an API (basically a dll) which contains Teacher School and Qualification Classes and DBOperation class to manage the CRUD operations.

Teacher and Qualification have Many to many Relationship (One particular teacher can have more than one education qualifications).

I managed to complete the code for One to many (teacher-Qualification) and successfully created the Controllers and views.

But I am stuck when it comes to Many to many.

Help needed in this. Thank you.

public class School
{
    public int SchoolID { get; set; }
    public string Name { get; set; }
    public string Telephone { get; set; }
    public string Address { get; set; }
}


public class Teacher
{
    public int TeacherID { get; set; }
    public string Name { get; set; }
    public string NIC { get; set; }
    public string Address { get; set; }
    public string Telephone { get; set; }
    public int School { get; set; }
    //public List<Qualification> Qualification { get; set; } if teacher got many Qualifications
    public int Qualification { get; set; }
}



public class Qualification
{
    public int QualificationID { get; set; }

    public string Type { get; set; }

}



public class DBOperations
{
    public List<Teacher> GetAllTeachers()
    {
        List<Teacher> t = new List<Teacher>();
        string connectionString = Connection.ConnectionString;
        SqlConnection conn = new SqlConnection(connectionString);
        conn.Open();
        SqlCommand cmd = conn.CreateCommand();
        cmd.CommandText = "SELECT * FROM Teachers";
        SqlDataReader dr = cmd.ExecuteReader();

        while (dr.Read()) 
        {
            Teacher teacher = new Teacher();
            teacher.TeacherID = dr.GetInt32(0);
            teacher.Name = dr.GetString(1);
            teacher.NIC = dr.GetString(3);
            teacher.Address = dr.GetString(4);
            teacher.Telephone = dr.GetString(4);
            teacher.School = dr.GetInt32(5);
            teacher.Qualification = dr.GetInt32(6);
            t.Add(teacher);


        }
        return t;

    }

    public void AddNewTeacher(Teacher teacher)
    {
        string Name = teacher.Name;
        string NIC = teacher.NIC;
        string Address = teacher.Address;
        string Telephone = teacher.Telephone;
        int School = teacher.School;
        int Qualification = teacher.Qualification;

        string connectionString = Connection.ConnectionString;
        SqlConnection conn = new SqlConnection(connectionString);
        conn.Open();
        SqlCommand cmd = conn.CreateCommand();
        cmd.CommandText = "INSERT INTO Teachers VALUES('" + Name + "','" + NIC + "','" + Address + "','" + Telephone + "','" + School + "','" + Qualification + "')";
        cmd.ExecuteNonQuery();
        conn.Close();
    }

}

Answer 1

Any many to many relationship will need an intermediate table. something like this:

public class TeachersQualifications
{
    public int QualificationId { get; set; }
    public int TeacherId { get; set; }
}

This would be the model representation. You could swap ID out with model if you would like. You will need a database table that resembles this model as well.

When you are adding your teacher you will also need to insert into this new table for each qualification that a teach has. One row for each qualification, including the TeacherId and the specific QualificationId .

When you go to retrieve the teacher you will also need to query this intermediate table by TeacherId to get the list of QualificationId s that the given teacher has. At this point you can then query the Qualification table to get the actual qualifications for the teacher. IF you want you could also do this in a single query using Joins.

Hopefully this helps.