I have a domain where an
Organization has People.
Organization Entity
public class
Organization {
private readonly List<Person> _people = new List<Person>();
public Person CreatePerson(string name) {
var person = new Person(organization, name);
_people.Add(person);
return person;
}
public IEnumerable<Person> People {
get { return _people; }
}
}
Person Entity
public class Person
{
public Person(Organization
organization, string name) {
if (organization == null) {
throw new ArgumentNullException("
organization");
}
Organization = organization;
Name = name;
}
public
Organization { get; private set; }
public Name { get; private set; }
}
The rule for this relationship is that a Person must belong to exactly one
Organization.
The invariants I want to guarantee are:
A person must have an
organization
this is enforced via the Person's constuctor
An
organization must know of its people
this is why the
Organization has a CreatePerson method
A person must belong to only one
organization
this is why the
organization's people list is not publicly mutable (ignoring the casting to List, maybe ToEnumerable can enforce that, not too concerned about it though)
What I want out of this is that if a person is created, that the
organization knows about its creation.
However, the problem with the model currently is that you are able to create a person without ever adding it to the organizations collection.
Here's a failing unit-test to describe my problem
[Test]
public void AnOrganizationMustKnowOfItsPeople()
{
var
organization = new Organization();
var person = new Person(organization, "Steve McQueen");
CollectionAssert.Contains(organization.People, person);
}
What is the most idiomatic way to enforce the invariants and the circular relationship?
