左加入Spring Data JPA规范

Question

假设我正在上以下课：（简化为极端）

@Entity
@Table(name = "USER")
public class User {

    @OneToOne(mappedBy = "user", cascade = CascadeType.ALL)
    private BillingAddress billingAddress;

    @OneToOne(mappedBy = "user", cascade = CascadeType.ALL)
    private ShippingAddress shippingAddress; // This one CAN be null

}

并且都*Address继承自此摘要：（再次简化了）

public abstract class Address {

    @OneToOne(optional = false, fetch = FetchType.LAZY)
    @JoinColumn(name = "USER_ID")
    private User user;

    @NotEmpty
    @Size(max = 32)
    @Column(name = "ADDR_TOWN")
    private String town;

 }

我尝试了JPA规范，如Spring的博客文章所述：

/**
 * User specifications.
 * 
 * @see <a href="https://spring.io/blog/2011/04/26/advanced-spring-data-jpa-specifications-and-querydsl">Advanced Spring Data JPA - Specifications and Querydsl</a>
 */
public class UserSpecifications {
    public static Specification<User> likeTown(String town) {
        return new Specification<User>() {
            @Override
            public Predicate toPredicate(Root<User> root, CriteriaQuery<?> query, CriteriaBuilder cb) {
                return cb.like(cb.lower(root.get("billingAddress").get("town")), '%' + StringUtils.lowerCase(town) + '%');
            }
        };
    }

使用此“规范”如下：

List<User> users = userRepository.findAll(UserSpecifications.likeTown(myTown));

但是现在，我也想在城镇中搜索shippingAddress，该地址可能不存在。我尝试将两者合并cb.like，cb.or但是结果SQL查询对shippingAddress具有一个INNER JOIN，这是不正确的，因为如上所述，它可能为null，所以我想要一个LEFT JOIN。

怎么做？

谢谢。

Answer 1

指定联接类型：

town = '%' + StringUtils.lowerCase(town) + '%';
return cb.or(
    cb.like(cb.lower(root.join("billingAddress", JoinType.LEFT).get("town")), town),
    cb.like(cb.lower(root.join("shippingAddress", JoinType.LEFT).get("town")), town));