Question

If I have an aggregate root which consists of say:

class Parent
{
    IEnumerable<Child> Children{ get; set; }
}

Children could contain any number of possible Child objects which are stored in the database.

What would be the best way of getting a total list of all Child objects to the application, so they can be presented in a UI allowing a user to attach/remove them from the Parent object?

Having a method in Parent such as

class Parent
{
    IEnumerable<Children> GetAllChildObjects { get; set; }
}

would surely corrupt the model with implementation details?

Would it be ok to have a domain service which calls the Parent repository and retrieves a full list. The facade to the application could then call the service directly, ensuring the Parent model stays “pure”.

Update:

To give a bit more detail, i’m tidying up a system and trying to give it some structure.

A User can hold a number of WorkLocations. WorkLocations are pretty simple. The current system contains a webpage which displays user details including a full list of valid WorkLocations. Selecting locations from the list updates the User model with the new locations.

Currently, the UI pretty much hits the DB and pulls out the full list of WorkLocations. I need to pull this back into a more structured form.

Or, does this suggest that WorkLocation should not be in the User root as it currently is?

Answer 1

Am I correct in thinking that you want all the WorkLocations from the database, regardless of what User they are attached to (if any)?

If so I would definitely go for the service approach, something like:

public interface IWorkLocationsService
{
    IEnumerable<WorkLocation> GetAllWorkLocations();
}

You might want WorkLocation to be immutable so that all changes to them go through User, though I suspect this isn’t necessary here.

Update:

You could then add the following methods to User

// This gets filled from the db somehow.
private IList<WorkLocation> workLocations;

// IEnumerable so that all external additions and
// removals must go through dedicated methods.
public IEnumerable<WorkLocation> WorkLocations
{
    get { return workLocations; }
}

public void AddWorkLocation(WorkLocation locationToAdd)
{
    workLocations.Add(locationToAdd);
    // Do whatever else you need to, i.e. mark the item for saving.
}

public void RemoveWorkLocation(WorkLocation locationToRemove)
{
    workLocations.Remove(locationToRemove);
    // Do whatever else you need to, i.e. mark the item for saving.
}