Question

I have two or more tables resembles each other.

PARENT
  ID   | PK
  NAME | VARCHAR

CHILD
  ID   |PK
  NAME | VARCHAR
  AGE  | INT

It’s not @Inheritance situation because they are independent entities and related to each other by @OneToMany or @ManyToOne.

I create entity class for each other.

@Entity
public class Parent {
    @Id
    private Long id;
    private String name;
    @ManyToOne(mappedBy = "parent")
    private Collection<Child> children;
}

@Entity
public class Child {
    @Id
    private Long id;
    private String name;
    private int age;
    @OneToMany
    private Parent parent;
}

Is there any nice way to share common fields mappings?

// @MappedSuperclass // is this what it is exactly for? 
public abstract class Base {
    // @Id protected Long id; // @@?
    @Column(name = "name", nullable = false)
    private String name;
}

@Entity
public class Parent extends Base {
    @Id
    @TableGenerator(...)
    @GeneratedValue(...)
    protected Long id;
    @ManyToOne(mappedBy = "parent")
    private Collection<Child> children;
}

@Entity
public class Child extends Base {
    @Id
    @TableGenerator(...)
    @GeneratedValue(...)
    protected Long id;
    private int age;
    @OneToMany
    private Parent parent;
}

Is this OK?
Is it even possible declaring @Id protected Long id; on the Base leaving @TableGenerator and @GeneratedVAlue on extended classes?

Answer 1

Is there any nice way to share common fields mappings?

MappedSuperclass is exactly right tool for that.

Is it even possible declaring @Id protected Long id; on the Base
leaving @TableGenerator and @GeneratedVAlue on extended classes?

No, it is not possible.