What is poco objects

It's really all about business rules. Where are my business rules? Go look in the classes in your domain layer. That's where you'll find them. Also, any discussion of DDD must include mention of Aggregrates research if you don't know. Lastly, I think domain object properties always must be valid.

If an invalid value is passed in, it should throw an exception, then and there. But what if you want a list of all invalid properties? Then pass in a DTO to a method that takes a DTO and adds exception handling around each setter to build out a list of errors.

If the list is not empty, then throw an exception from that method that returns the full details of all invalid properties.

Just to clarify my previous post, you shouldn't have a Validate method on your domain object, because then you are assuming that the client is going to call the Validate method. Instead, the domain object should always be valid. In addition, validation on child objects of an aggregrate should be placed in the aggregate, and those child objects should not be exposed to the outside world only the aggregate is exposed.

Rather, the aggregate can expose a property, if needed, that wraps the child object and thus gives the aggregate a chance to validate any changes being made to the child object.

Hi Anonymous. You're stating a few things that are definitely just your opinion as though they are fact and accepted best practice. To say that POCOs shouldn't have validation because you shouldn't be able to create them unless the data is valid is nonsense.

But if you have code that demonstrates a different design, post a link to it. I would love to take a look. Good post Rudy. So who calls the repository? Any reason you're not cascading your constructors?

Much thanks for the article. Hmm, this brings some questions in my mind. Now the question is - what should a mapper map then? I agree that sometimes there may be no reasons to map to a POCO. For example, if I know that all I want is a bunch of records and maybe even with paging that I want to feed to some report-like web form then I do not need to bother with POCO when reading data.

When the user choses a record and clicks "Edit" - then I can construct a POCO if needed - if there is some business logic for reading but I guess that is rarely so, then again DTO will be good. It would serialize over XML automatically just fine if I need to use it with web services.

This would not be a good PI. What if they want to validate some fields in setters? Then my domain object must inherit from DTO so designers can override setters as needed - but again not a PI-ish to force inheriting.

Why not set the setter of the PersonGuid to internal to protect it for the Gui? Overall, an interesting post. Some questions and concerns came to mind some of which are similar to previous comments. It just feels wrong that Validate has a side effect. The code given below defines a POCO class.

To create POCO classes, we first need to disable auto create classes or auto-create code generation, which generates Context classes entity code in Model1. To disable this code generation, right-click on model1. After removing the value Custom tool, you will see that in modal1.

Now, double-click on Modal1. A screen will open from where you need to select ADO. But are they really synonyms? DTO is a class representing some data with no logic in it. You can look at them as dumb bags of information the sole purpose of which is to just get this information to a recipient. On the other hand, Value Object is a full member of your domain model. It conforms to the same rules as Entity. It means that two Value Objects with the same property set should be considered the same whereas two Entities differ even if their properties match.

Value Objects do contain logic and, typically, they are not used for transferring data between application boundaries.

It's not unusual to add metadata to a DTO in order to have it support model validation or similar purposes. Such attributes do not add any behavior to the DTO itself, but rather facilitate behavior elsewhere in the system. Thus, they do not break the "rule" stating that DTOs should contain no behavior. The term DTO is extremely vague. All it says is that an object consists only of data, not behavior. It says nothing about its intended use. In many architectures, DTOs can serve a number of roles.

These DTOs are typically called ViewModels, and ideally they should have no behavior, only data formatted as the View expects it.

However, be careful. So, it's important to consider the context before making any broad assumptions. Whenever possible, name your DTOs according to their intended use.

Naming a class FooDTO gives no indication of how or where that type should be used in the application's architecture. Instead, favor intention-revealing names like FooViewModel. Encapsulation is an important principle of object-oriented design. But it doesn't apply to DTOs. Encapsulation is used to keep collaborators of a class from relying too heavily on specific implementation details about how the class performs its operations or stores its data.

Since DTOs have no operations or behavior, and should have no hidden state, they have no need for encapsulation. Don't make your life harder by using private setters or trying to make your DTOs behave like immutable value objects. Your DTOs should be simple to create, simple to write, and simple to read. They should support serialization without the need for any custom work to support it.