And again: How to solve 'Repeated column in mapping for collection'?

Question

I'm trying to use HashMap in entity Player and my HashMap is a compound of Integer and another entity (entity ResourceOnPlayerAccount) that is in a One-To-Many relationship, so I can prevent duplicated entries but still can keep the newest entry. My code worked well with a HashSet but that way I couldn't keep the newest entries.

I already searched for another post. Among these posts, I found this one Another Repeated column in mapping for entity error But in this post, the problem seems to be the repeated call of a column, but in my code, I can't find something like that. And also I couldn't find an example with a HashMap.

I added the Player entity as followed:

Player.java

@Entity
@Table(name="player")
public class Player {

    // define fields

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name="id")
    private int id;

    @Column(name="user_name")
    private String userName;

    @Column(name="password")
    private String password;

    @Column(name="display_name")
    private String displayName;

    @Column(name="email")
    private String email;

    // define relationships

//    @OneToMany(cascade = CascadeType.ALL)
//    @JoinColumn(name = "player_id")
//    private Set<ResourceOnPlayerAccount> resourceOnPlayerAccountSet;

    @OneToMany
    @MapKeyColumn(name = "player_id")
    private Map<Integer, ResourceOnPlayerAccount> resourceOnPlayerAccountMap;
...

The commented lines are my previous implementation with HashSet that had worked.

Following is the other entity class:

ResourceOnPlayerAccount.java

@Entity
@Table(name = "resources_on_player_account")
public class ResourceOnPlayerAccount {

    // define fields

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private int id;

    @Column(name = "amount")
    private double amount;

    @Column(name = "resource_id")
    private int resourceId;
...

I just want to make sure that a player does not have duplicate resources in his account and that existing amounts of resources can be updated.

Answer 1

@MapKeyColumn is used in a Map<Basic, Basic> situation.

In your case, it is Map<Basic, Entity>. For this @MapKey is used:

Specifies the map key for associations of type java.util.Map when the map key is itself the primary key or a persistent field or property of the entity that is the value of the map.