StackOverflow2013

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copied!<blockquote> <p>Move validation outside of the entity itself.</p> </blockquote> <p>One instructor shouldn't know about all other instructors. Validation against set of instructors isn't responsibility of one particular instructor.</p> <blockquote> <p>Allow for access to a instructor repository from necessary entities that are attempting to perform this validation.</p> </blockquote> <p>Domain model should be persistence ignorant. Need to break that indicates flaws in Your model.</p> <blockquote> <p>Create a service that allows access to a list of instructors by instrument category.</p> </blockquote> <p>This bit of information reveals lack of aggregate root - I would call it <code>InstrumentClass</code>. </p> <p>Introducing that into Your model would solve some of Your issues. <code>InstrumentClass</code> would hold available instructors that teaches particular instrument.</p> <p>Next thing You need to figure out is how to describe properly student that is assigned to class. Unfortunately I can't name it at the moment (maybe <code>Participation</code>?). But that entity would be used for <code>InstrumentClass</code> to figure out which instructors are too busy.</p> <hr> <p>Here's my "free-style" (just to show what I see) on modeling Your domain:</p> <pre><code>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{ } </code></pre>

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