Question 259311 in Json Question posted in
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How to map JSON in a Java object

I’m trying to transform this JSON in a Java object. But I’m struggling with this conversion.

{
    "id": "c01cede4-cd45-11eb-b8bc-0242ac130003",
    "publisherId": "nintendo",
    "name": "Mario",
    "timePlayed": {
        "2023-05-01": 10,
        "2023-05-02": 2,
        "2023-05-03": 3,
        "2023-05-04": 4
    }
}

First, I created a class named GameData and I was able to save the first 3 parameters with no problem at all.
My difficult is with parameter timePlayed. I tried to create another class named TimePlayed, using the annotation Entity–relationship model but I have no success with that. Also, I tried to use a Map instead using the object TimePlayed but it did not work as well.
As you can see, inside the timePlayed is a date and an integer.
This is the code that I have while writing this question:

Class GameData:

@Table(name = "GAME_DATA")
@Entity
@Data
public class GameData {

    @Id
    @GeneratedValue(strategy = GenerationType.UUID)
    private String gameDataId;

    private String publisherId;
    private String name;

    private Map<Date, String> timePlayed;


}

Class TimePlayed

@Table(name = "TIME_PLAYED")
@Data
@Entity
public class TimePlayed {
    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE)
    @Column(name = "id", nullable = false)
    private Long id;

    private Map<String, Integer> playedDateAndTime;

}

My guess that using a second class is not the best approach but this what I was capable to do so far and, of course, is not working at all.
I got a some errors like:

  • Object references an unsaved transient instance – save the transient instance before flushing hibernate JPA
  • ‘Basic’ attribute type should not be a map
Tags:

2

Answers


  1. Chosen as BEST ANSWER
    0

    I was able to resolve my problem using this the class this way:

    @Table(name = "GAME")
@Entity
@Data
public class Game {

    @Id
    @GeneratedValue(strategy = GenerationType.UUID)
    private String gameDataId;

    private String publisherId;
    private String name;

    @ElementCollection
    @MapKeyColumn(name = "date")
    @Column(name = "time_played")
    @DateTimeFormat(pattern = "yyyy/mm/dd")
    private Map<LocalDate, Integer> timePlayed;

}

    This way, I could save and show the JSON the way I need.


  2. 0

    Usually converting to map is a very non-trivial task, I would suggest changing the structure of the json itself, if this is possible, for example, to this:

    {
    "id": "c01cede4-cd45-11eb-b8bc-0242ac130003",
    "publisherId": "nintendo",
    "name": "Mario",
    "timePlayed": [
      {
        "date":"2023-05-01",
        "time": 10
      },
      {
        "date":"2023-05-02",
        "time": 2
      },
      {
        "date":"2023-05-03",
        "time": 3
      },
      {
        "date":"2023-05-04",
        "time": 4
      },
    ]
}

    This will allow you to bring your classes to this form:

    public class GameData{
    public String id;
    public String publisherId;
    public String name;
    public List<TimePlayed> timePlayed;
}

public class TimePlayed{
    public LocalDate date;
    public inttime;
}

    As for your mistakes, it’s hard to say without details, but most likely this is due to the fact that the child entity needs to be preserved to the same extent as the parent or use cascade types. JPA Cascade Types / Baeldang

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