DTO and JPA Version

Ok. Problem 1: getting DTO's from entities:

Since your entities can expose their data publicly you can access their properties and instantiate DTO object or simply serialise the entity directly

Problem 2 : Entities from DTO's:

A constructor method which takes a list of the properties to be set can be called using the properties of the DTO

Problem 3 : large entities when you only need summary info

Create a new summary object which you can retrieve from the repository. Note I suggest you make strongly typed repositories with methods like Repo.GetMyObjectById(string id) rather than expose a generic ORM.

Problem 4 : where to orchestrate all this.

My recommendation is to have a service class one level below your hosting service/app/website.

This has access to the repositories DTO's and entities and its methods map to the controllers/service calls of your application so that you do not need any code at the top level and can host the same service in multiple ways.

Giving it access to the repos is not an issue when you can only use them to retireve entities rather than doing any query they like.

Putting this assembly/orchestration logic inside the entity is usually bad as you will want the entity to be reused for other purposes.

This top level service should be very light. Just, get these objects, call this method, create and return the result/DTO/viewmodel

Because its so light its not a massive prob if you skip the layer and put the code in your controller. But it will save you time if you change the hosting layer and help with testing etc

First of all, merely citing someone's article on the Internet does not constitute sufficient justification for changing a practice. You have to weigh the pros and cons, and make up your own mind.

Note that the author of the article you cited hates ORM's. He follows a strict principle of encapsulating code with its data, which is sort of the foundational principle of object-orientation. He strongly dislikes ORM because it strips classes of their intelligence, and he's not wrong about that.

In his ORM hate article, he writes (more or less) that classes should be responsible for saving themselves to the database, a practice that violates a principle called "persistence ignorance." Persistence ignorance simply means that classes shouldn't know anything about their database overlord, and it's difficult to achieve this in any realistic manner with ORM's. He gets around the persistence ignorance problem by using interfaces, making his data ignorant of its underlying implementation.

To be fair, I write code that looks a lot like his under the hood, albeit a bit more streamlined than his (Java has a reputation for being very verbose, and I don't bother with the DTO interfaces). After wrestling with Entity Framework for awhile, I began using Dapper and writing SQL queries instead. I get better performance, less complexity and finer targeting of the database.

The class that implements your so-called "data transfer object" is a nice place to put this code; all you have to do is hand it an IdbConnection object, and the class has all it needs to read from and persist itself to the database.

I guess my question is, why does this have to be an either/or choice? If you need something from the database that requires a DTO, then use a DTO. If you want what you're calling a "domain object," then use that instead.