CODEWITHSUNDEEP
javahibernatejpa
bashar
bashar

Reputation: 415

Mapping multiple rows from the same database into a single entity

I am looking for the best way to map multiple rows in one table into a single entity. The database table I have is shown below:

principal_id    permission    target
12312313        PERM1         1000
12312313        PERM2         1000
12312313        PERM2         1002

Ideally I would like to map the contents of this table into my Principal @Entity as a field as follows:

@Entity
...
public class Principal {
    @Id
    private long principalId;

    ...

    private Map<String, List<Long>> permissionMap;

}

What is the best way to do so?

Upvotes: 3

Views: 2124

Answers (2)

Tom Anderson
Tom Anderson

Reputation: 47163

I don't know of a way to do exactly what you want. The closest i can get is:

@Embeddable
public class Permission {
    private String permission;
    private int target;
}

@ElementCollection
@CollectionTable(name="foo", joinColumns = @JoinColumn(name = "principal_id"))
private Set<Permission> permissions;

If you only had one permission per target, then you could use a map:

@ElementCollection
@CollectionTable(name="foo", joinColumns = @JoinColumn(name = "principal_id"))
@MapKeyColumn(name="permission")
@Column(name="target")
private Map<String, Integer> permissions;

Sadly, i don't think there's a way to do this for a map containing collections.

Upvotes: 3

Angel Villalain
Angel Villalain

Reputation: 595

I would suggest the following structure:

@Entity
...
public class Principal {

    @Id
    private long principalId;
    /** Other properties **/
    @OneToMany
    private Set<Permission> permissions;
....
}

@Entity
@IdClass(PermissionId.class)
public class Permission {
    @Id
    private String permission;
    @Id
    private Long target

    public static class PermissionId implements Serializable {
        private String permission;
        private Long target;
        /** setters/getters hashcode and equals goes here **/
    }
}

Upvotes: -1

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