Re: Avoid injecting Service/Repository in an Entity

You don't want to pull in every student with a repository, if you had a
decent amount of students  your performance will suck.

// you can implement this delegate with a simple sql statement
public delegate bool IsCurrentlyEnrolled(Student student);

public class Class {
  public void Enroll(Student student, IsCurrentlyEnrolled
isCurrentlyEnrolled) {
    Guard.Against(isCurrentlyEnrolled(student), "blah");
    ...
  }
}

Of course if you want this to scale there will be a chance that one could
'get through;' you will need to detect this and prompt for administrative
action down the line.


On Tue, Mar 25, 2014 at 10:15 AM, Jorge Branco
<[email protected]>wrote:

>
>
> From my (limited) understanding, you'd have to implement that kind of
> logic on a command that knows all the relevant services/repositories.
>
>
> On Tue, Mar 25, 2014 at 7:23 AM, <[email protected]> wrote:
>
>>
>>
>> Hi Everyone,
>>
>> From what I've read, this is really bad. But I have the following use
>> case so wondering how to do this in the proper DDD way. The business rule
>> is contrived but it is very similar to what i have in real life. I just
>> cannot disclose the use case due to NDAs.
>>
>> I have a class named Class. A class can have students in it. There is a
>> business rule such that if a student with the same surname belongs to any
>> current of any other class, they cannot be added to the class.
>>
>> So on Class, i have a method named AddStudent. Just wondering how would
>> the algorithm be implemented in a proper DDD sense
>>
>> public class Class
>> {
>>
>> public void AddStudent(Student student)
>> {
>>
>> // Call a repository to get all the students enrolled in all classes
>> // If any students surname matches the surname of the student passed in,
>> do not thing
>> // otherwise add the student
>>
>> }
>>
>> }
>>
>>
>>
>>
>>
>
>
> 
>



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