How to get single value from another table as String

Question

I've got two tables

Logs:

-------------------------------------------------------------------------------
|   id (pk)             |   target                    |      event_code (fk)   |
-------------------------------------------------------------------------------
|   1                   |   System_Role               |           1            |
--------------------------------------------------------------------------------
|   2                   |   System_RUle               |           2            |
--------------------------------------------------------------------------------
|   1                   |   Internal_User             |           3            |
--------------------------------------------------------------------------------
|   3                   |   External_User             |           4            |
--------------------------------------------------------------------------------

Events:

-------------------------------------------------------
|   id (pk)             |             event           |
-------------------------------------------------------
|   1                   |   Role was added            |
-------------------------------------------------------
|   2                   |   Rule was removed          |
-------------------------------------------------------
|   1                   |   User was updated          |
-------------------------------------------------------
|   3                   |   User password was reseted |
-------------------------------------------------------

Table logs has foreign key from field event_code to event's field id.

Entity:

@Entity
@Table(name = "logs")
public class LogEvent implements Serializable{

    private static final long serialVersionUID = 1;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "id")
    private Integer id;
    @Basic(optional = false)
    @NotNull
    @Size(min = 1, max = 150)
    @Column(name = "target")
    private String target;

    //????
    private String event;

    public LogEvent(String target, String event) {
        this.target = target;
        this.event = event;
    }        
}

I need to get field event from table Events and put it to variable event. And also I need to add new values correctly to my DB. How to do that?

Answer 1

What you need here, is to use a ManyToOne relationship with JPA, such as:

@ManyToOne 
@JoinColumn(name="event_code", nullable=false)
private Event event;

This way you can easily manipulate the Event register corresponding to your LogEvent.

I strongly recommend you to learn about JPA relationships: https://www.tutorialspoint.com/jpa/jpa_entity_relationships.htm