Java Spring Boot | Adding additional data to response model

[Redan Hassoun]

Hi,

I am building an endpoint that fetches Quizzes object list.

The Quiz model looks like this:

@Entity
@Access(AccessType.FIELD)
@Table(name = DBConsts.QUIZ_TABLE_NAME)
public class Quiz extends BaseModel{
    @Id
    @GeneratedValue(generator = "UUID")
    @GenericGenerator(
            name = "UUID",
            strategy = "org.hibernate.id.UUIDGenerator")
    @Column(name=DBConsts.QUIZ_ID)
    private String id;

    @NotNull(message = "Title cannot be null")
    @Size(max = 512)
    private String title;

    @Lob
    private String description;

    private String imageUrl;

    @Column(nullable = false)
    @NotNull(message = "public property cannot be null")
    private Boolean isPublic;

    private String assignedUsers;

    @Column(nullable = false)
    @NotNull(message = "Creator id cannot be null")
    private String creatorId;

    @OneToMany(mappedBy = "quiz",
               cascade = CascadeType.ALL)
    private Set<QuizAnswer> answers = new HashSet<>();

    @OneToMany(mappedBy = "quiz",
               cascade = CascadeType.ALL)
    private Set<UserAnswer> userAnswers = new HashSet<>();

    /* Getters and setters */

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Quiz quiz = (Quiz) o;
        return Objects.equals(id, quiz.id) &&
                Objects.equals(creatorId, quiz.creatorId);
    }

    @Override
    public int hashCode() {
        return Objects.hash(id, creatorId);
    }
}

And here is an example of the endpoint response:

[
   {
       "createdAt": "2019-08-17T12:00:43.522+0000",
       "updatedAt": "2019-08-17T12:00:43.522+0000",
       "id": "bf013209-9e00-4890-8c74-a40298b51e12",
       "title": "quiz v",
       "description": "This quiz is called quiz v and it is just an example, this text should be the description of the quiz",
       "imageUrl": "https://images.immediate.co.uk/production/volatile/sites/3/2018/04/Screen-Shot-2018-04-05-at-09.20.50-96984e5.png",
       "isPublic": true,
       "assignedUsers": null,
       "creatorId": "620a1b29-94f3-4f55-b55c-51b173d35113",
       "answers": [
           {
               "createdAt": "2019-08-17T12:00:43.522+0000",
               "updatedAt": "2019-08-17T12:00:43.522+0000",
               "id": "69d3ed74-4382-44f4-b874-f9fc9c2f2181",
               "content": "answer x",
               "isCorrect": true,
               "userAnswers": [
                   {
                       "createdAt": "2019-08-17T12:02:31.070+0000",
                       "updatedAt": "2019-08-17T12:02:31.070+0000",
                       "id": "2e749bff-08a8-4f20-8709-7bf3a76cbafe"
                   }
               ]
           }
       ],
       "userAnswers": [
           {
               "createdAt": "2019-08-17T12:02:31.070+0000",
               "updatedAt": "2019-08-17T12:02:31.070+0000",
               "id": "2e749bff-08a8-4f20-8709-7bf3a76cbafe"
           }
       ]
   },
   {
       "createdAt": "2019-08-17T12:00:43.514+0000",
       "updatedAt": "2019-08-17T12:00:43.514+0000",
       "id": "a2c8e185-2bd2-4f2a-b6b5-f5f6139b377d",
       "title": "quiz o",
       "description": "This quiz is called quiz o and it is just an example, this text should be the description of the quiz",
       "imageUrl": "https://images.immediate.co.uk/production/volatile/sites/3/2018/04/Screen-Shot-2018-04-05-at-09.20.50-96984e5.png",
       "isPublic": true,
       "assignedUsers": null,
       "creatorId": "620a1b29-94f3-4f55-b55c-51b173d35113",
       "answers": [
           {
               "createdAt": "2019-08-17T12:00:43.514+0000",
               "updatedAt": "2019-08-17T12:00:43.514+0000",
               "id": "53a398f7-f4ec-48e7-9551-54f2b6f90159",
               "content": "answer x",
               "isCorrect": true,
               "userAnswers": []
           }
       ],
       "userAnswers": []
   }
]



I want to have the ability to add additional information in each item of the response array,
for example, i want to add the "number-of-correct-answers" for each quiz object

But without adding an attribute to the "Quiz" class because it represents the table on DB


How can I achieve this?

My goal is to be able to have an additional information in the JSON response without altering my table


Thanks in advance,
Redan

[Puspender Tanwar]

Adding an answer for future users.
Yes you can as many fields as you want into your response. There are 2 situations for returning a response for a request:
1. The client wants the exact similar data as the DB table has, or 2 3 extra fields.
2. There need to a lot of extra fields and their are some additional fields which require some calculation or some other entity data. Like Post can have a PostType json field.

Solutions for 1:
Simply return the fetched entity. If you want to hide some field (e.g id), use @JsonIgnore on it.
If you want 2 3 additional fields, create those fields into your Entity class and mark them as @Transient. @Transient mark that field to not be included in SQLs generated by ORM

Solution for 2:
Use Dtos(Data Transfer Object). Add as many field as you want to them. Then either use setters to feed data into that DTO or use some library like MapStruct to automap data from Entity to DTO.

And that's it, you have your own flavor of response.

Now if you even wants to take advantage of HATEOAS, you can easily do that with your DTO.