访问数据以进行验证并使用DDD确定默认值

Move validation outside of the entity itself.

一位教师不应该了解所有其他教师.对一组教师的验证不是一个特定教师的责任.

Allow for access to a instructor repository from necessary entities that are attempting to perform this validation.

域模型应该是持久性无知的.需要打破,表明你的模型中存在缺陷.

Create a service that allows access to a list of instructors by instrument category.

这一点信息显示缺少聚合根 – 我称之为InstrumentClass.

将其引入您的模型可以解决您的一些问题. InstrumentClass将聘请教授特定乐器的教师.

接下来你需要弄清楚的是如何恰当地描述分配给班级的学生.不幸的是,我现在无法命名(也许是参与？).但该实体将用于InstrumentClass以确定哪些教师太忙.

在我的域建模中,这是我的“自由风格”(只是为了展示我所看到的)：

using System;

public class Main{
  public Main(){
    var instructor = new Instructor();
    var instrument = new Instrument("saxaphone");
    var saxaphoneClass = new InstrumentClass(saxaphone,teacher);
    var me=new Person("Arnis");
    //here,from UI,I can see available classes,choose one
    //and choose according instructor who's assigned to it
    var request=me.RequestEnrollment(saxaphoneClass,instructor);
    saxaphoneClass.EnrollStudent(request);
  }
}
public class Person{
  public IList<EnrollmentRequest> EnrollmentRequests { get; private set; }
  public EnrollmentRequest RequestEnrollment
   (InstrumentClass instrumentClass,Instructor instructor){
    if (!instrumentClass.IsTeachedByInstructor(instructor))
      throw new Exception("Instructor does not teach this music instrument");
    var request=new EnrollmentRequest(this,instrumentClass,instructor);
    EnrollmentRequests.Add(request);
    return request;
  }
}
public class EnrollmentRequest{
  public Person Person{ get; private set; }
  public InstrumentClass InstrumentClass { get; private set; }
  public Instructor Instructor{ get; private set; }
}
public class InstrumentClass{
  public void EnrollStudent(EnrollmentRequest request){
    var instructor=request.Instructor;
    var student=new Student(request.Person);
    var studies=new Studies(this,student,instructor);
    //TODO: this directiveness isn't good
    //student/instructor should listen for class events themselves
    //and class should listen if by any reason instructor or student cannot
    //participate in studies
    student.EnrollInClass(studies);
    instructor.AssignStudent(studies);
    Studies.Add(studies);
  }
  public bool IsTeachedByInstructor(Instructor instructor){
    return Instructors.Contains(instructor);
  }
  public InstrumentClass
   (Instrument instrument,params Instructor[] instructors){
    Instrument=instrument; Instructors=instructors.ToList();
  }
  public IList<Instructor> Instructors{get;private set;}
  public IList<Studies> Studies { get; private set; }
  public Instrument Instrument { get; private set; }
}
public class Studies{
  public Student Student { get; private set; }
  public Instructor Instructor { get; private set; }
  public InstrumentClass InstrumentClass { get; private set; }
}
public class Student{
}
public class Instructor{
}
public class Instrument{
}