Should i use model classes or payload classes to serialize a json response

Question

I'm using spring boot with mysql to create a Restful API. Here's an exemple of how i return a json response.

first i have a model:

@Entity
public class Movie extends DateAudit {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private Date releaseDate;
    private Time runtime;
    private Float rating;
    private String storyline;
    private String poster;
    private String rated;

    @OneToMany(mappedBy = "movie", cascade = CascadeType.ALL, orphanRemoval = true)
    private List<MovieMedia> movieMedia = new ArrayList<>();

    @OneToMany(mappedBy = "movie", cascade = CascadeType.ALL, orphanRemoval = true)
    private List<MovieReview> movieReviews = new ArrayList<>();

    @OneToMany(mappedBy = "movie", cascade = CascadeType.ALL, orphanRemoval = true)
    private List<MovieCelebrity> movieCelebrities = new ArrayList<>();

    // Setters & Getters
}

and correspond repository:

@Repository
public interface MovieRepository extends JpaRepository<Movie, Long> {
}

Also i have a payload class MovieResponse which represent a movie instead of Movie model, and that's for example if i need extra fields or i need to return specific fields.

public class MovieResponse {

    private Long id;
    private String name;
    private Date releaseDate;
    private Time runtime;
    private Float rating;
    private String storyline;
    private String poster;
    private String rated;
    private List<MovieCelebrityResponse> cast = new ArrayList<>();
    private List<MovieCelebrityResponse> writers = new ArrayList<>();
    private List<MovieCelebrityResponse> directors = new ArrayList<>();

    // Constructors, getters and setters

    public void setCelebrityRoles(List<MovieCelebrityResponse> movieCelebrities) {
        this.setCast(movieCelebrities.stream().filter(movieCelebrity -> movieCelebrity.getRole().equals(CelebrityRole.ACTOR)).collect(Collectors.toList()));
        this.setDirectors(movieCelebrities.stream().filter(movieCelebrity -> movieCelebrity.getRole().equals(CelebrityRole.DIRECTOR)).collect(Collectors.toList()));
        this.setWriters(movieCelebrities.stream().filter(movieCelebrity -> movieCelebrity.getRole().equals(CelebrityRole.WRITER)).collect(Collectors.toList()));
    }
}

As you can see i divide the movieCelebrities list into 3 lists(cast, directos and writers)

And to map a Movie to MovieResponse I'm using ModelMapper class:

public class ModelMapper {

    public static MovieResponse mapMovieToMovieResponse(Movie movie) {

        // Create a new MovieResponse and Assign the Movie data to MovieResponse
        MovieResponse movieResponse = new MovieResponse(movie.getId(), movie.getName(), movie.getReleaseDate(),
                movie.getRuntime(),movie.getRating(), movie.getStoryline(), movie.getPoster(), movie.getRated());

        // Get MovieCelebrities for current Movie
        List<MovieCelebrityResponse> movieCelebrityResponses = movie.getMovieCelebrities().stream().map(movieCelebrity -> {

            // Get Celebrity for current MovieCelebrities
            CelebrityResponse celebrityResponse = new CelebrityResponse(movieCelebrity.getCelebrity().getId(),
                    movieCelebrity.getCelebrity().getName(), movieCelebrity.getCelebrity().getPicture(),
                    movieCelebrity.getCelebrity().getDateOfBirth(), movieCelebrity.getCelebrity().getBiography(), null);

            return new MovieCelebrityResponse(movieCelebrity.getId(), movieCelebrity.getRole(),movieCelebrity.getCharacterName(), null, celebrityResponse);
        }).collect(Collectors.toList());

        // Assign movieCelebrityResponse to movieResponse
        movieResponse.setCelebrityRoles(movieCelebrityResponses);
        return movieResponse;
    }
}

and finally here's my MovieService service which i call in the controller:

@Service
public class MovieServiceImpl implements MovieService {

    private MovieRepository movieRepository;

    @Autowired
    public void setMovieRepository(MovieRepository movieRepository) {
        this.movieRepository = movieRepository;
    }

    public PagedResponse<MovieResponse> getAllMovies(Pageable pageable) {

        Page<Movie> movies = movieRepository.findAll(pageable);

        if(movies.getNumberOfElements() == 0) {
            return new PagedResponse<>(Collections.emptyList(), movies.getNumber(),
                    movies.getSize(), movies.getTotalElements(), movies.getTotalPages(), movies.isLast());
        }

        List<MovieResponse> movieResponses = movies.map(ModelMapper::mapMovieToMovieResponse).getContent();
        return new PagedResponse<>(movieResponses, movies.getNumber(),
                movies.getSize(), movies.getTotalElements(), movies.getTotalPages(), movies.isLast());
    }
}

So the question here: is it fine to use for each model i have a payload class for the json serialize ? or it there a better way.
also guys id it's there anything wrong about my code feel free to comment.

score 2 · Accepted Answer · answered Sep 11 '18 at 20:59

I had this dilemma not so long back, this was my thought process. I have it here https://stackoverflow.com/questions/44572188/microservices-restful-api-dtos-or-not

The Pros of Just exposing Domain Objects

The less code you write, the less bugs you produce.
- despite of having extensive (arguable) test cases in our code base, I have came across bugs due to missed/wrong copying of fields from domain to DTO or viceversa.
Maintainability - Less boiler plate code.
- If I have to add a new attribute, I don't have to add in Domain, DTO, Mapper and the testcases, of course. Don't tell me that this can be achieved using a reflection beanCopy utils like dozer or mapStruct, it defeats the whole purpose.
- Lombok, Groovy, Kotlin I know, but it will save me only getter setter headache.
DRY
Performance
- I know this falls under the category of "premature performance optimization is the root of all evil". But still this will save some CPU cycles for not having to create (and later garbage collect) one more Object (at the very least) per request

Cons

DTOs will give you more flexibility in the long run
- If only I ever need that flexibility. At least, whatever I came across so far are CRUD operations over http which I can manage using couple of @JsonIgnores. Or if there is one or two fields that needs a transformation which cannot be done using Jackson Annotation, As I said earlier, I can write custom logic to handle just that.
Domain Objects getting bloated with Annotations.
- This is a valid concern. If I use JPA or MyBatis as my persistent framework, domain object might have those annotations, then there will be Jackson annotations too. If you are using Spring boot you can get away by using application-wide properties like mybatis.configuration.map-underscore-to-camel-case: true , spring.jackson.property-naming-strategy: SNAKE_CASE

Short story, at least in my case, cons didn't outweigh the pros, so it did not make any sense to repeat myself by having a new POJO as DTO. Less code, less chances of bugs. So, went ahead with exposing the Domain object and not having a separate "view" object.

Disclaimer: This may or may not be applicable in your use case. This observation is per my usecase (basically a CRUD api having 15ish endpoints)

score 1 · Answer 2 · answered Sep 08 '18 at 14:54

We should each layer separate from other. As in your case, you have defined the entity and response classes. This is right way to separate things, we should never send the entity in the response. Even for request thing we should have a class.

What the issue if we are sending entity instead of response dto.

Not available to modify them because we already expose it with our client
Sometimes we don't want to serialize some fields and send as response.

Some overhead are there to translate request to domain, entity to domain etc. But its okay to keep more organized. ModelMapper is the best choice for translation purpose.

Try to use construct injection instead of setter for mandate dependency.

score 1 · Answer 3 · answered Sep 10 '18 at 16:58

It is always recommended to separate DTO and Entity. Entity should interact with DB/ORM and DTO should interact with client layer(Layer for request and response) even if the structure of Entity and DTO same.

Here Entity is Movie and DTO is MovieResponse

Use your existing class MovieResponse for request & response.
Never use Movie class for request & response. and the class MovieServiceImpl should contain business logic for converting Entity to DTO, Or you can use Dozer api to do auto conversion.

The reason for sepating:

In case you need to add/remove new elements in Request/response you dont have to change much code
if 2 entity have 2 way mapping(e.g. one-to-many/many-to-many relationship) then JSON object cant be created if object have nested data, this will throw error while serializing
if Anything changed in DB or Entity, then this will not affect JSON Response(most of the time).
Code will be clear and easy to maintain.

S.K. · Answer 4 · 2018-09-10T17:41:43.547

DTO is a design pattern and solves the problem of fetching as maximum useful data from a service as possible.

In case of a simple application as yours, the DTOs tend to be similar to the Entity classes. However for certain complex applications, DTOs can be extended to combine data from various entities to avoid multiple requests to the server and thus save valuable resources and request-response time.

I would suggest not to duplicate the code in a simple case like this and use model classes in response to the APIs as well. Using separate response classes as DTOs will not solve any purpose and will only make maintaining the code difficult.

score 1 · Answer 5 · answered Sep 10 '18 at 17:40

On one side you should separate them because sometimes some of the JPA annotations which you use in your model don't work well with the json processor annotations. And yes, you should keep the things separated.

What if you later decide to change your data layer? Will you have to rewrite all your client side?

On the other side, there is this problem of mapping. For that, you can use a library with a small performance penalty.

score 0 · Answer 6 · answered Aug 06 '19 at 08:11

While most people have answered pros and cons of using DTO objects, I would like to give my 2 cents. In my case DTO was necessary because not all fields persisted in database were captured from user. There were a few fields which were computed based on user input(of other fields) and were not exposed to users. Also, it can also reduces the size of payload which could result in better performance in such cases.

score 0 · Answer 7 · answered Jul 20 '21 at 13:49

I advocate for separating the "Payload" or "Data" object from the "Model" or "Display" object. Pretty much always. This just keeps things easier to manage.

Here's an example: Let's say you need to hit an API that gives you data about cats for sale. Then you parse the data into a cat model object and populate a list of cats that is then displayed to the user. Cool.

But now you want to integrate another API and pull cats from 2 databases. But you run into a problem. One API returns furColor for the color and the new one returns catColor for the color.

If you were using the same object to also display the info, you have some options:

Add both furColor and catColor to the model object, make them both optional, and do some kind of computed property to check which one is set and use that one to display the color
- In reality, this is rarely an option because the responses will usually be much more different than just one value like this so you would likelly need a whole new parser anyway
Add a new data object and then also a new adapter and then have to do some kind of check to know which adapter to use when
Something else that still isn't pretty or fun to work with

However, if you create a data object that catches the response, and then a display object that has only the info needed to populate the list, this becomes really easy:

You have a data object that captures the response from the first API
Now make a data object that captures the response from the second API
Now all you need is some kind of simple mapper to map the response to the Display Object
Now both will be converted to a common simple display object, and the same adapter can be used to display the new cats without additional work

This also will make storing the data locally much cleaner.

Should i use model classes or payload classes to serialize a json response

7 Answers7

The Pros of Just exposing Domain Objects

Cons