冬眠。 如何使用条件从联接表中进行查询？

Question

I have 2 tables:

|shops        |       |discounts    |
|-------------|       |-------------|
|id           |       |id           |
|name         |       |title        |
                      |shop_id      |

*UML Diagram

And entities:

@Entity
@Table(name = "shops")
public class Shops {
  @Id
  @GeneratedValue
  @Column(name="id", unique=true, nullable=false)
  protected Integer id;

  @Column(name="name", length=45, nullable=false)
  protected String name;

  @OneToMany(fetch = FetchType.LAZY, mappedBy = "shop")
  private Set<Discounts> discounts = new HashSet<Discounts>(0);
        //getters & setters
}

@Entity
@Table(name="discounts")
public class Discounts {
@Id
  @GeneratedValue
  @Column(name="id")
  private Integer id;

  @Column(name="title")
  private String title;

  @ManyToOne(fetch = FetchType.LAZY)
  @JoinColumn(name = "shop_id", nullable = false)
  private Shops shop;
        //getters & setters
}

I need to receive all discounts which belong to a shop usingCriteria. I try to make it as follows:

Criteria cr = session.createCriteria(Discounts.class);
cr.add(Restrictions.eq("id", shop.getLocality()));
List<Discounts> discounts = cr.list();

But I get an error:

java.lang.ClassCastException: exmp.entity.Discounts_$$_jvste43_1 cannot be cast to java.lang.Integer

How can I fix this error?

Answer 1

You can do this:

Criteria cr = session.createCriteria(Discounts.class);
cr.add(Restrictions.eq("shop", shop)); //assuming shop is an object of Shops
List<Discounts> discounts = cr.list();

This will internally map the id column of Shops to shop column of Discounts to check the constraints and return results.

Answer 2

The documentation says that idEq applies to an identifier property.

https://docs.jboss.org/hibernate/core/3.3/api/org/hibernate/criterion/Restrictions.html#idEq(java.lang.Object)

Instead you can try something like this:

Criteria cr = session.createCriteria(Discounts.class);
cr.createAlias("shop","shop") 
cr.add(Restrictions.eq("shop.id",<yourid>));

But if you just load a shop with its id, you will be getting the all the discounts of that shop since you have bidirectional relationship.

Criteria cr = session.createCriteria(Shops.class);
cr.add(Restrictions.idEq(<yourid>));