JPA Cascade Type : PERSIST vs MERGE (Why choose what?)

@NoArgsConstructor(access = AccessLevel.PROTECTED) @Entity @Table(name = "tb_order") @Getter @DynamicUpdate @DynamicInsert public class Order extends BaseEntity { ,,, @JsonIgnore @ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.PERSIST) private User buyer; @JsonIgnore @ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.PERSIST) private User seller; }