JPA Criteria Building 中的两侧连接答案

【问题标题】：Two-side Joining in JPA Criteria BuildingJPA Criteria Building 中的两侧连接
【发布时间】：2020-03-04 07:00:25
【问题描述】：

我有三个实体，就像这样：-

@Entity
@Table(name = "product")
public class Product {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "id")
    @Expose
    private long id;

    @ManyToOne
    @JoinColumn(name = "users_id")
    @Expose
    private User user;
}

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

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "id")
    @Expose
    private long id;
}


@Entity
@Table(name = "users_phone")
public class UserPhone {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "id")
    @Expose
    private int id;

    @ManyToOne
    @JoinColumn(name = "users_id")
    @Expose
    private User user;
}

现在，我想从基于连接三个表的产品表中获取结果。所以我制定了一个规范，以便我可以将它传递到存储库中。这是规范的代码。

    Specification<ProductPost> productSpecification = new Specification<ProductPost>() {
        @Override
        public Predicate toPredicate(Root<ProductPost> root, CriteriaQuery<?> criteriaQuery, CriteriaBuilder criteriaBuilder) {
            List<Predicate> predicates = new ArrayList<>();
            criteriaQuery = criteriaBuilder.createQuery();

            if (userName.length() > 0) {
                predicates.add(criteriaBuilder.like(root.join("user").<String>get("fullName"), "%" + userName + "%"));
            }
            if (phoneNumber.length() > 0) {
                // Below line isn't working actually as  join("UserPhone") - 'user' table has no reference for 'userPhone'. But 'userPhone' has 'user'.
                predicates.add(criteriaBuilder.like(root.join("user").join("UserPhone").<String>get("phoneNumber"), "%" + postType + "%"));
            }

            return criteriaBuilder.and(predicates.toArray(new Predicate[predicates.size()]));
        }
    };

是的，如果我在 'user' 表中有 'userPhone' 引用，例如 product -> user -> userPhone 而不是 product -> user, userPhone -> user，这将很容易。但我的架构是这样的。现在我在加入 3 个表并获取结果时遇到了麻烦。

【问题讨论】：

标签： java spring-boot jpa criteria-api dynamicquery

【解决方案1】：

如果cross-join 被占用而不是join 你可以试试这个解决方案

if (phoneNumber.length() > 0) {
    Root<UserPhone> userPhone = query.from(UserPhone.class);

    predicates.add(criteriaBuilder.equal(
        root.join("user").get("id"), 
        userPhone.get("user").get("id")
    ));

    predicates.add(criteriaBuilder.like(
        userPhone.get("phoneNumber"), 
        "%" + postType + "%"
    ));
}

【讨论】：