DDD validation on full object graph

@Value
@Builder
public class Parent {

    @NotNull
    private String firstName;
    private Child child;

@Builder
public class Child {

    @NotNull
    private String firstName;

here is my challenge, we are doing DDD and we do the validation of objects within constructor or via a build method (builder pattern). What's I would like to achieve is to be able to construct the full object tree in a way that I can collect all validation errors.

As you can see with the following code, I will with this only collect the errors of the child missing the missing firstname of the parent.

Note that these objects are created manually, otherwise, I would just add @Valid's and such, but I don't think this can work when you do build objects manually.

FYI : I use the spring boot stack.

Parent.builder()
                .firstName(null)
                .child(Child.builder()
                        .firstName(null)
                        .build())
                .build();

I generally dissociate validation and domain models.

For example, I apply validation on the views representing a request body (see an example of such validation here) and then try to instantiate the value object only once I am sure that validation passed. In your case, it means that you will put your annotations on the views, not the VOs.

Note that it does not make sense to apply validation on a VO: the fact that you were able to create it implies that all constraints are already met.

For providing a list of errors from domain model objects I usually collect all the potentially produced errors in the aggregate root which again collects the potential errors from its child domain objects. This approach follows the idea to collect errors instead of immediately throwing exceptions at the first occurrence of an error.

You can look into this answer which already illustrates an example of such an approach (although it is C# code the pattern is language agnostic).

If you are using the spring stack here would be an approach:

Create a new @Component called ParentFactory. the factory encapsulates the creation of valid objects in DDD.

inside of this factory you can use builder patterns or constuctor calls - it does not matter since object creation is abstracted away.

Furthermore the ParentFactory gets the javax Validator injected and thus is able to perform the mentioned task above

In DDD your Entities are not responsible for doing things like "collecting" errors unless that is part of your ubiquitous language. What you want to do is have the entities raise a DomainEvent and you can use a single listener to collect and consume all the raised events.