JPA CriteryQuery内部联接-IllegalStateException

Question

I have the following qriteria query in JPA:

      CriteriaBuilder cb2 = entityMager.getCriteriaBuilder();
      CriteriaQuery<DemoUser> cqInnerJoin = cb2.createQuery(DemoUser.class);
      Root<DemoUser> root = cqInnerJoin.from(DemoUser.class);
      Join<DemoUser, DemoOrder> join = root.join("userId", JoinType.INNER);

But it throws exception:

Exception in thread "main" java.lang.IllegalStateException: CAN_NOT_JOIN_TO_BASIC (There is no English translation for this message.)
    at org.eclipse.persistence.internal.jpa.querydef.FromImpl.join(FromImpl.java:354)
    at org.eclipse.persistence.internal.jpa.querydef.FromImpl.join(FromImpl.java:513)
    at jpaTest.jpaTest.main(jpaTest.java:144)

I generated these classes from Oracle database tables. Is there something wrong with my code?

I tried this in TypedQuery, but it displayed the same error message.

The generated classes:

DemoUser.class

 @Entity
    @Table(name="DEMO_USERS")
    public class DemoUser implements Serializable {
        private static final long serialVersionUID = 1L;

        @Id
        @GeneratedValue(strategy=GenerationType.IDENTITY)
        @Column(name="USER_ID")
        private long userId;

        //bi-directional many-to-one association to DemoOrder
        @OneToMany(mappedBy="demoUser")
        //@JoinColumn(name = "USER_ID")
        private List<DemoOrder> demoOrders;

DemoOrder class

@Entity
@Table(name="DEMO_ORDERS")
public class DemoOrder implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="ORDER_ID")
    private long orderId;

    @Temporal(TemporalType.DATE)
    @Column(name="ORDER_TIMESTAMP")
    private Date orderTimestamp;

    @Column(name="ORDER_TOTAL")
    private BigDecimal orderTotal;

    //bi-directional many-to-one association to DemoCustomer
    @ManyToOne
    @JoinColumn(name="CUSTOMER_ID")
    private DemoCustomer demoCustomer;

    //bi-directional many-to-one association to DemoUser
    @ManyToOne
    @JoinColumn(name="USER_ID")
    private DemoUser demoUser;

    //bi-directional many-to-one association to DemoOrderItem
    @OneToMany(mappedBy="demoOrder")
    private List<DemoOrderItem> demoOrderItems;

Answer 1

When it is required to join, you should always be aware to do it on an association . The association between DemoOrder and DemoUser is mapped by the field demoUser (as you have taken DemoUser as root ),so here is what you should do:

Join<DemoUser, DemoOrder> join = root.join("demoUser", JoinType.INNER);

Answer 2

You can not join to the attribute "userId" that is of a basic type(long). For a singular attribute, you can join to an Entity or Embeddable type.