DDD：更新实体的多个属性的指南

Question

So, i decided to learn DDD as it seems to solve some architectural problems i have been facing. While there are lots of videos and sample blogs, i have not encountered one that guides me to solve the following scenario:

Suppose i have the entity

public class EventOrganizer : IEntity
{
    public Guid Id { get; }

    public string Name { get; }

    public PhoneNumber PrimaryPhone { get; }

    public PhoneNumber AlternatePhone { get; private set; }

    public Email Email { get; private set; }

    public EventOrganizer(string name, PhoneNumber primaryPhoneNr)
    {
        #region validations

        if (primaryPhoneNr == null) throw new ArgumentNullException(nameof(primaryPhoneNr));

        //validates minimum length, nullity and special characters
        Validator.AsPersonName(name);

        #endregion

        Id = new Guid();
        Name = name;
        PrimaryPhone = primaryPhoneNr;
    }
}    

My problem is: suppose this will be converted and fed to a MVC view and the user wants to update the AlternatePhone, the Email and a lot of other properties that make sense to exist within this entity for the given bounded context (not shown for brevity)

I understand that the correct guidance is to have a method for each operation, but (AND I KNOW ITS KINDA OF ANTI-PATTERN) i cant help but wonder if this wont end up triggering multiple update calls on the database.

How is this handled ? somewhere down the line, will there be something that maps my EventOrganizer to something - say DbEventOrganizer and gathers all changes made to the domain entity and apply those in a single go?

Answer 1

DDD is better suited for task-based UIs. What you describe is very CRUD-oriented. In your case, individual properties are treated as independent data fields where one or many of these can be updated by a single generic business operation (update).

You will have to perform a deeper analysis of your domain than this if you want to be successfull with DDD.

Why would someone update all those fields together? What implicit business operation is the user trying to achieve by doing that? Is there a more concrete business process that is expressed by changing PrimaryPhone , AlternatePhone and Email together?

Perhaps that is changing the ContactInformation of an EventOrganizer ? If that's the case then you could model a single ChangeContactInformation operation on EventOrganizer . Your UI would then send a ChangeContactInformation command rather than an update command.

As for the persistence of your aggregate roots (AR), this is usually handled by an ORM like NHibernate if you are using a RDBMS. However, there are other ways to persist your ARs like Event Sourcing, NoSQL DBs and even storing JSON or any other data inter-change formats in a RDBMS.

Answer 2

You question is quite broad!

EventOrganizer itself should not be updating anything. You should keep your update code quite separate from the entity. A different class would take an EventOrganizer object and update the DB. This is called 'persistence ignorance' and makes the code a lot more modular and cohesive.

It would be common to create a View Model - a class whose purpose is to provide the View with the exact data it needs in the exact form it needs. You would need to create the View Model from your EventOrganizer, after which the View can update it - programmatically or with binding. When you're ready to save the changes, you'll need to update your EventOrganizer from the View Model and pass it onto the updater. This seems like a layer you don't need when the project is small and simple, but it is becomes invaluable as the complexity builds.