java 休眠：org.hibernate.loader.MultipleBagFetchException：无法同时获取多个包

Hibernate : org.hibernate.loader.MultipleBagFetchException: cannot simultaneously fetch multiple bags

提问by ketchyn

Entity classes

实体类

Customer

顾客

       @Entity
        @Table(name="Custumer")
        public class Custumer implements Serializable {

            @Id
            @GeneratedValue(strategy = GenerationType.IDENTITY)
            @Column(name="id")
            private Long id;
            @Column(name="name",unique = true)
            private String name;
            @Column(name="Email",unique = true)
            private String Email;
            @Column(name = "Coins")
            private Double coins;

            @ManyToMany(fetch = FetchType.EAGER,cascade = CascadeType.ALL)

            private List<ShippingAdress> shippingAdress = new ArrayList<ShippingAdress>();


            @OneToMany( fetch = FetchType.EAGER, mappedBy = "custumer", cascade = CascadeType.ALL,orphanRemoval = true)

            private List<Order> orders= new LinkedList<Order>();
//...

ShippingAdress

送货地址

    @Entity
        @Table(name="ShippingAdress")
        public class ShippingAdress implements Serializable {

            @Id
            @GeneratedValue(strategy = GenerationType.IDENTITY)
            @Column(name="id")
            private Long id;
            @Column(name="postCode")
            private String PostCode;
            @Column(name="street")
            private String street;
            @Column(name="house")
            private String house;
            @Column(name="flat")
            private String flat;

            @ManyToMany(mappedBy = "shippingAdress")
            private List<Custumer> custumers = new LinkedList<Custumer>();
    //...

Items

项目

@Entity
    @Table(name="Items")
    public class Items implements  Serializable,Comparable<Items>  {

        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)

        @Column(name="id")
        private Long id;
        @Column(name="name", unique = true)
        private String name;
        @Column(name="price")
        private double price;
        @Column(name="count")
        private int count;

        @OneToMany(mappedBy = "item", cascade = CascadeType.ALL,orphanRemoval = true)
        List<Order> orders = new LinkedList<Order>();
    //...

CustomerOrder

客户订单

@Entity
@Table(name = "CustumerOrder")
public class Order implements Serializable {
    @Id
    @ManyToOne
    private Custumer custumer;


    @Id
    @ManyToOne

    private Items item;

When I'm trying to get all orders from particular customer

当我试图从特定客户那里获得所有订单时

  public List<Order> getOrderByCustumerId(Custumer custumer) {

        Criteria criteria = session.createCriteria(Order.class);
        List<Order> res = (List<Order>) criteria.add(Restrictions.eq("custumer",custumer)).list();

        return res;
    }

I'm facing the following exception:

我面临以下异常：

org.hibernate.loader.MultipleBagFetchException: cannot simultaneously fetch multiple bags

If delete fetch = FetchType.EAGERfrom one of the places they are existed getting the following: (supposed deleted from customer )

如果fetch = FetchType.EAGER从它们存在的地方之一删除，则会得到以下结果：（假设从客户中删除）

   org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: org.CoinsShop.DataBase.DataSets.Custumer.shippingAdress, could not initialize proxy - no Session

relations in DB

DB中的关系

回答by JMSilla

As the exception says to you, you can't fetch two related collections or bags simultaneously. A quick solution would be to remove the FetchType.EAGERfrom one collection and force the fetching of that collection explicitly calling the collection objects.

正如例外告诉你的那样，你不能同时获取两个相关的集合或包。一个快速的解决方案是FetchType.EAGER从一个集合中删除 ，并强制显式调用集合对象来获取该集合。

For example, if you remove the FetchType.EAGERfrom shippingAddresscollection, you can force the fetching like this:

例如，如果您删除FetchType.EAGERfromshippingAddress集合，您可以像这样强制获取：

public List<Order> getOrderByCustomerId(Customer customer) {
    Criteria criteria = session.createCriteria(Order.class);
    List<Order> res = (List<Order>) criteria.add(Restrictions.eq("customer",customer)).list();

    for (Order order : res)
        order.getCustomer().getShippingAddress().size();

    return res;
}

Calling the size()method of the collection will force the fetching of all the elements of that collection.

调用size()集合的方法将强制获取该集合的所有元素。

More information about this topic:

有关此主题的更多信息：

Hibernate cannot simultaneously fetch multiple bags

Hibernate 不能同时取多个包