休眠实体循环引用产生StackOverflowError

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问题描述

当我尝试具有引用 Product 和 Product 的 Order 时，出现 StackOverflowError 引用 Order .我知道这是由于有一个循环参考，但是我不确定如何解决它.我是ORM的新手，但不是SQL/Schema Design的新手:通常，我会有一个 Ordered_Products 表，该表将 Order 映射到 Product ，但我认为Hibernate会自动为我解决这个问题.

I get a StackOverflowError when attempting to have an Order which references a Product, and a Product that references an Order. I know this is due to having a circular reference, but I am unsure as to how to fix it. I'm new to ORMs but not to SQL/Schema Design: typically, I would have a Ordered_Products table which maps an Order to a Product, but I thought Hibernate would automagically take care of that for me.

Product 都具有唯一的ID(这些ID在应用程序外部生成)，因此没有两个 Product 是相同的. Order ID也会在应用程序外部生成(我将在此管道的较早过程中从CSV导入此数据).

Products all have unique IDs (these are generated outside the app), so no two Products are the same. Order IDs are also generated outside the app (I will be importing this data from a CSV in an earlier process in this pipeline).

有人可以协助我们前进吗?

Could someone assist with moving forward?

@Entity
@Table(name = "Orders")
class Order implements Serializable {

    private static final long serialVersionUID = 2916987431893884948L;

    @Id
    @Column(name="id")
    private Long id;

    @Column(name="contactName")
    private String contactName;

    @OneToMany(mappedBy = "order", fetch=FetchType.EAGER, cascade = CascadeType.ALL)
    private Set<Product> products;

    // ...plain old getters and setters omitted...

    public Set<Product> getProducts() {

        // Should this be done at the member variable declaration?
        if (null == products) {
            this.products = new HashSet<Product>();
        }

        return products;
    }

    public void addProduct(Product p) {
        p.setOrder(this);
        getProducts().add(p);
    }

    public String toString() {
    /* plain old to String which prints all member vars */
    }
}

Product.java

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

    private static final long serialVersionUID = 663408095532480033L;

    @Id
    @Column(name="id")
    private String id;

    @Column(name="size")
    private Size size;

    @OneToOne
    @JoinColumn(name="order_id", nullable=false)
    private Order order;

    // ...plain old getters and setters...

    public enum Size {
        EMPTY,
        XXSMALL,
        XSMALL,
        SMALL,
        MEDIUM,
        LARGE
    }

    public String toString() {
    /* plain old to String which prints all member vars */
    }
}

产生错误的代码

Product b = new Product();
b.setId("ABC123");
b.setSize(Product.Size.LARGE);

Product c = new Product();
c.setId("DEF456");
c.setSize(Product.Size.XSMALL);

Order o = new Order();
o.setId(551234L);
o.setContactName("Marco");
o.addProduct(b);
o.addProduct(c);
System.out.println("Order ID=" + o);

堆栈跟踪

Exception in thread "AWT-EventQueue-0" java.lang.StackOverflowError
    at java.util.HashMap$KeyIterator.<init>(HashMap.java:1451)
    at java.util.HashMap$KeySet.iterator(HashMap.java:912)
    at java.util.HashSet.iterator(HashSet.java:172)
    at java.util.AbstractCollection.toString(AbstractCollection.java:454)
    at java.lang.String.valueOf(String.java:2979)
    at java.lang.StringBuilder.append(StringBuilder.java:131)
    at com.code4armour.shippingtracker.ui.model.Order.toString(Order.java:207)
    at java.lang.String.valueOf(String.java:2979)
    at java.lang.StringBuilder.append(StringBuilder.java:131)
    at com.code4armour.shippingtracker.ui.model.Band.toString(Band.java:78)
    at java.lang.String.valueOf(String.java:2979)
    at java.lang.StringBuilder.append(StringBuilder.java:131)
    at java.util.AbstractCollection.toString(AbstractCollection.java:462)
    at java.lang.String.valueOf(String.java:2979)
    at java.lang.StringBuilder.append(StringBuilder.java:131)
    at com.code4armour.shippingtracker.ui.model.Order.toString(Order.java:207)
    at java.lang.String.valueOf(String.java:2979)
    at java.lang.StringBuilder.append(StringBuilder.java:131)
    at com.code4armour.shippingtracker.ui.model.Band.toString(Band.java:78)

这里的问题是 Order.toString()调用 Product.toString()，反之亦然

The problem here is the Order.toString() calling the Product.toString(), and vice versa

the