Spring Data JPA - ManyToMany - JPQL - 存储库中的@Query 形成答案

【问题标题】：Spring Data JPA - ManyToMany - JPQL - @Query formation in RepositorySpring Data JPA - ManyToMany - JPQL - 存储库中的@Query 形成
【发布时间】：2019-08-08 07:39:33
【问题描述】：

我有一个使用 PostgreSQL RDBMS 的 spring boot 项目。我在两个实体（客户和产品）之间有 @ManyToMany 关系。他们由 customer_product 加入。但是在存储库层形成 JPQL 时，我遇到了困难。这是实体：

@Entity
@NamedQuery(name="Customer.findAll", query="SELECT c FROM Customer c")
public class Customer implements Serializable {

... all properties ... getter setter constructor...

//bi-directional many-to-many association to Product
    @JsonIgnore
    @ManyToMany
    @JoinTable(
        name="customer_product"
        , joinColumns={
            @JoinColumn(name="customer_id")
            }
        , inverseJoinColumns={
            @JoinColumn(name="product_id")
            }
        )
    private List<Product> products;

@Entity
@NamedQuery(name="Product.findAll", query="SELECT p FROM Product p")
public class Product implements Serializable {
... all properties ... getter setter ... constructors ...

//bi-directional many-to-many association to Customer
    @JsonIgnore
    @ManyToMany(mappedBy="products")
    private List<Customer> customers;

稍后在存储库中：

@Repository
public interface CustomerRepository extends CrudRepository<Customer, Integer> {

//Below mentioned query works perfectly as Customer & Address has OneToMany Relation

@Query("select new com.arindam.springjpa.springdatajpaexamples.vo.CustomerDetailsVO(c.id, c.customerName, a.fullAddress) from Customer c, Address a where c.address.addressId=a.addressId")
    List<CustomerDetailsVO> findAllCustomerDetails();

// But I need help on below query
// I want to find out full details of ManyToMany relation between customer & product

@Query("select new com.arindam.springjpa.springdatajpaexamples.vo.CustomerProductAddressDetailsVO(c.id, c.customerName, a.fullAddress, p.productName) from Customer c, Address a, Product p where c.address.addressId=a.addressId and c.products.product.productId=p.productId")

List<CustomerProductAddressDetailsVO> findAllCustomerAddressProductDetails();

这里的VO有结果是简单的VO类

@Entity
public class CustomerProductAddressDetailsVO {

    private Integer id;
    private String customerName;
    private String fullAddress;
    private String productName;

//Like a simple POJO with getter setter constructors

你能推荐一下吗？

感谢您的宝贵反馈。

【问题讨论】：

您需要使用连接（即使对于您的第一个查询）。见docs.jboss.org/hibernate/orm/current/userguide/html_single/…。第一个查询实际上应该看起来像select new ... from Customer c join c.address。我会让你阅读文档并找出第二个应该是什么。
@JB Nizet - 非常感谢。第一个查询完美运行。但是第二个有问题。第二个查询是多对多，因此是两个列表。所以无法加入。
您尝试了哪些查询，结果如何？

标签： java spring-boot spring-data-jpa jpql

【解决方案1】：

我已经解决了这个问题。由于实体类是使用 Eclipse 插件生成的，所以没有生成 customer_product 的类。所以我手动生成它并使用查询。所以最终的代码是：

@Entity
@Table(name="customer_product")
@NamedQuery(name="CustomerProduct.findAll", query="SELECT c FROM CustomerProduct c")
public class CustomerProduct implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    private Integer id;

    @Column(name="customer_id")
    private Integer customerId;

    @Column(name="product_id")
    private Integer productId;

和存储层：

@Query("select new com.arindam.springjpa.springdatajpaexamples.vo.CustomerProductAddressDetailsVO(cp.id, c.customerName, a.fullAddress, p.productName) from Customer c, Address a, Product p, CustomerProduct cp "
            + "where c.address.addressId=a.addressId and cp.productId=p.productId and cp.customerId=c.id")
    List<CustomerProductAddressDetailsVO> findAllCustomerAddressProductDetails();

效果很好。

【讨论】：