A DTO (Data Transfer Object) is an object that defines how the data will be sent over the network or application. On the other hand Response Object which usually holds response data from DTO's or WebApi's or Data Access or any other responses to client.
The Response Object which usually includes all/few properties of a particular model or entity or DTO which is usually a subset of DTO object. Please see below example.
Employee Response Object:
public class EmployeeResponseObject
{
public int Id { get; set; }
public string Name { get; set; }
public string Designation { get; set; }
}
Employee DTO:
public class EmployeeDTO
{
public int Id { get; set; }
public string Name { get; set; }
public string Designation { get; set; }
public decimal Salary { get; set; }
public DateTime JoiningDate { get; set; }
public decimal Tax { get; set; }
}
Now you can see here. EmployeeResponseObject is a subset of EmployeeDTO which mean's EmployeeResponseObject has fewer properties from EmployeeDTO. In few scenario's we don't have to pass all information to end Client. So we will use EmployeeResponseObject to get required properties from EmployeeDTO.
You can use LINQ to project data to Response Object from DTO.
[ResponseType(typeof(EmployeeResponseObject))]
public EmployeeResponseObject GetEmployee()
{
var employee = from e in dbContext.EmployeeDTO
select new EmployeeResponseObject()
{
Id = e.Id,
Name = e.Name,
Designation = e.Designation
};
return employee;
}
If you use only EmployeeDTO to pass information to presentation layer/View, Webforms or ConsoleApp then your presentation layer/View will tightly coupled to your domain layer. Any changes done to DTO Objects requires you to change presentation layer or controllers which is not a good way to do it.
Sometimes DTO and Response Objects will be exactly same then why to use separate objects.
This might look unnecessary duplication of code but think when your project grows bigger specially in a big teams where many people work together on different layers of application. Here using DTO and separate Response object makes much more sense with a good programming practice. Presentation layer/View and the domain layer will become tightly coupled when you skip using ResponseObject/ViewModelObject.
