JPA Entities: how to check recursive parents

I have a simple entity representing a group.

 public class Group {
 Long id;
 String name;

 @JoinColumn(name = "idparent", nullable = true, referencedColumnName = "ID")
 @ManyToOne(targetEntity = Group.class, fetch = FetchType.EAGER, cascade = {}, optional = true)
 private Group parent;
 }

A group can be the parent of some groups.

During tests I set A.parent = A, so the A object fall in recursion.

Is there an annotation or something to check the following constraint?

a.id != a.parent.id

You can create a custom validator and class level annotation constraint, bind a validator class using the Constraint annotation of validation api.

@Constraint(validatedBy = GroupConstraintValidator.class)
@Target({TYPE })
@Retention(RUNTIME)
public @interface GroupConstraint {
    	String message() default "Invalid TestA.";
    	Class<?>[] groups() default {};
		Class<? extends Payload>[] payload() default {};
}

Create the validator class with the validation logic to check a.id != a.parent.id

public class GroupConstraintValidator implements ConstraintValidator<GroupConstraint, Group>{

	@Override
	public boolean isValid(Group object, ConstraintValidatorContext context) {
		 if (!(object instanceof Group)) {
	            throw new IllegalArgumentException("@CustomConstraint only applies to TestA");
	        }
		 Group group = (Group) object;
		 if (group.getParent() != null && group.getParent().getId() == group.getId()) {
			 return false; 
		 }
		 return true;
	}
}

Apply this constraint to the entity class, Group.

@Entity
@GroupConstraint
public class Group {

	@Id
	@GeneratedValue(strategy = GenerationType.AUTO)
	@Column(name= "ID",unique = true)
	private Long id;

	private String name;

	@JoinColumn(name = "IDPARENT", nullable = true, referencedColumnName = "ID")
	@ManyToOne(targetEntity = Group.class, fetch = FetchType.EAGER, cascade = {}, optional = true)
	private Group parent;

Now the validation provider should through a constraint violation during lifecycle callbacks , that is when child references itself.

Group child = new Group();
//set attributes
child.setParent(child);
em.persist(child);