When do we need to create a new custom DTO?

Question

I had an Entity named User that can have many services (Entity Service) and I have two actions one of them with the name GetUser() and the other with name GetUserServices()

• GetUser(): fetch the user and return an Custom DTO with name UserDto

public class UserDto
{
public int Id {get;set;}
public string Username {get;set;}
} 

• GetUserServices(): fetch the user and its services ids, let's say at some point I want to return on this function these properties [UserId, Username, ServicesIds] my question is should I modify the UserDto by adding ServicesId property [1] or create another Custom DTO [2]?

---

1. If I go with the solution [1] means that GetUser() will return a JSON object with empty ServicesId property and that's will lead to bad UX
2. If I go with the solution [2] that will lead to create for each action I had, a custom DTO depends on the shape of data returned, and also I'll struggle with figure out the name for each created custom DTO.

Answer 1

You can use either ways. If you use separate DTO per operation - it's a lot of code writing (and time spending). I prefer to use one DTO for similar operations as long as they are readable and flexible and create additional if needed.

For more information have a look in this doc.You can find here some basic principles, pros and cons of DTO.

https://docs.microsoft.com/en-us/aspnet/web-api/overview/data/using-web-api-with-entity-framework/part-5