Spring data JPA和hibernate分离实体传递以持久化ManyToMany关系

我正在尝试保留一个与已保留的其他对象具有多对多关系的对象。

这是我的持久化对象（它们已经持久化在数据库中，这是一个 MySql）：-

Product

@Entity
@Table(name="PRODUCT")
public class Product {
    private int productId;
    private String productName;
    private Set<Reservation> reservations = new HashSet<Reservation>(0);

    @Id @GeneratedValue(strategy=GenerationType.AUTO)
    public int getProductId() {
        return productId;
    }

    public void setProductId(int productId) {
        this.productId = productId;
    }

@Column(nullable = false)
    public String getProduct() {
        return product;
    }
    public void setProduct(String product) {
        this.product = product;
    }

    @ManyToMany(fetch = FetchType.LAZY, mappedBy = "products")
    public Set<Reservation> getReservations() {
        return reservations;
    }
    public void setReservations(Set<Reservation> reservations) {
        this.reservations = reservations;
    }
}

这是我正在尝试创建的非持久对象

@Entity
@Table(name = "RESERVATION")
public class Reservation {

    private int reservationId;

    private Set<Product> products = new HashSet<Product>(0);

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    public int getReservationId() {
        return reservationId;
    }

    public void setReservationId(int reservationId) {
        this.reservationId = reservationId;
    }

    @ManyToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    @JoinTable(name = "product_reservation", joinColumns = { @JoinColumn(name = "reservationId", nullable = false, updatable = false) }, inverseJoinColumns = { @JoinColumn(name = "productId", 
            nullable = false, updatable = false) })
    public Set<Product> getProducts() {
        return products;
    }

    public void setProducts(Set<Product> products) {
        this.products = products;
    }
}

这是我的ReservationService类，它接收产品名称数组，使用该名称查找产品并将它们放入预订对象中。

@Service
public class ReservationServiceImpl implements ReservationService {

    @Autowired
    private ProductDAO productDAO;
    @Autowired
    private ReservationDAO reservationDAO;

    @Transactional
    public void createReservation(String[] productNames) {

            Set<Product> products = new HashSet<Product>();
            for (String productName : productNames) {
                Product pi = productDAO.findByProductName(productName);
                products.add(pi);
            }
            Reservation reservation = new Reservation();
            reservation.setProducts(products);
            reservationDAO.save(reservation);   ---> Here I am getting detached entity passed to persist
    }
}

这是我的ProductDAO界面：

public interface ProductDAO extends JpaRepository<Product, Integer> {

    public Product findByProductName(String productName);
}

这是我的弹簧配置文件：

@Configuration
@PropertySource(value = { "classpath:base.properties" })
@EnableTransactionManagement
@EnableJpaRepositories(basePackages = "com.reservation.dao")
public class RepositoryConfig {

    @Autowired
    private Environment env;

    @Bean
    public static PropertySourcesPlaceholderConfigurer placeHolderConfigurer() {
        return new PropertySourcesPlaceholderConfigurer();
    }

    @Bean
    public PlatformTransactionManager transactionManager() {
        EntityManagerFactory factory = entityManagerFactory().getObject();
        return new JpaTransactionManager(factory);
    }

    @Bean
    public LocalContainerEntityManagerFactoryBean entityManagerFactory() {
        HibernateJpaVendorAdapter vendorAdapter = new HibernateJpaVendorAdapter();
        vendorAdapter.setGenerateDdl(Boolean.valueOf(env
                .getProperty("hibernate.generate.ddl")));
        vendorAdapter.setShowSql(Boolean.valueOf(env
                .getProperty("hibernate.show_sql")));

        Properties jpaProperties = new Properties();
        jpaProperties.put("hibernate.hbm2ddl.auto",
                env.getProperty("hibernate.hbm2ddl.auto"));
        jpaProperties.put("hibernate.dialect", env.getProperty("hibernate.dialect"));

        LocalContainerEntityManagerFactoryBean factory = new LocalContainerEntityManagerFactoryBean();
        factory.setDataSource(dataSource());
        factory.setJpaVendorAdapter(vendorAdapter);
        factory.setPackagesToScan("com.reservation.service.domain");
        factory.setJpaProperties(jpaProperties);
        factory.afterPropertiesSet();
        factory.setLoadTimeWeaver(new InstrumentationLoadTimeWeaver());
        return factory;
    }

    @Bean
    public HibernateExceptionTranslator hibernateExceptionTranslator() {
        return new HibernateExceptionTranslator();
    }

    @Bean
    public DataSource dataSource() {
        BasicDataSource dataSource = new BasicDataSource();
        dataSource.setDriverClassName(env.getProperty("jdbc.driverClassName"));
        dataSource.setUrl(env.getProperty("jdbc.url"));
        dataSource.setUsername(env.getProperty("jdbc.username"));
        dataSource.setPassword(env.getProperty("jdbc.password"));
        return dataSource;
    }
}

这是完整的堆栈跟踪：

严重：路径 [/web] 上下文中 servlet [dispatcher] 的 Servlet.service() 引发异常 [请求处理失败； 嵌套异常是 org.springframework.dao.InvalidDataAccessApiUsageException：传递给持久化的分离实体：com.reservation.service.domain.Product； 嵌套异常是 org.hibernate.PersistentObjectException: 分离的实体传递给持久化: com.reservation.service.domain.Product] 其根本原因 org.hibernate.PersistentObjectException：传递给持久化的分离实体：com.reservation.service.domain.Product 在 org.hibernate.event.internal.DefaultPersistEventListener.onPersist（DefaultPersistEventListener.java:141）

我遇到了同样的问题并通过删除解决了它cascade = CascadeType.PERSIST.

在你的情况下你使用CascadeType.ALL，这相当于也使用 PERSIST，根据文档 https://javadoc.io/static/javax.persistence/persistence-api/1.0-rev-1/javax/persistence/CascadeType.html:

定义传播到关联实体的一组可级联操作。值cascade=ALL 相当于cascade={PERSIST, MERGE, REMOVE, REFRESH, DETACH}。

这意味着当您尝试保存预订时reservationDAO.save(reservation)它还会尝试保留关联的 Product 对象。但该对象未附加到此会话。所以会出现错误。