java - 如何使用 Hibernate 正确注释 List<Interface>？

Question

我刚刚开始学习如何使用 Hibernate，但我无法弄清楚如何在引用接口(interface)时正确地注释列表。

这是我的情况，我有一个像这样实现 MarketOrder 的类 MarketOrderImpl ...

@Entity
public final class MarketOrderImpl implements MarketOrder {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private String id;
private OrderType type;
private BigDecimal price;
private BigDecimal quantity;
private BigDecimal total;

public MarketOrderImpl(OrderType type, BigDecimal price, BigDecimal 
quantity, BigDecimal total) {
    this.type = type;
    this.price = price;
    this.quantity = quantity;
    this.total = total;
}

我有一个 MarketOrderBookImpl，它有两个我无法无一异常(exception)地注释的列表(私有(private)列表 sellOrders 和私有(private)列表 buyOrders)

@Entity
public final class MarketOrderBookImpl implements MarketOrderBook {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private String marketId;

@OneToMany @JoinTable(name="marketorderimpl")
@MapKeyColumn(name="id")
private List<MarketOrder> sellOrders;

@OneToMany @JoinTable(name="marketorderimpl")
@MapKeyColumn(name="id")
private List<MarketOrder> buyOrders;


public MarketOrderBookImpl(String marketId, List<MarketOrder> 
sellOrders, List<MarketOrder> buyOrders) {
    this.marketId = marketId;
    this.sellOrders = sellOrders;
    this.buyOrders = buyOrders;
}

这是我的异常(exception)...

Caused by: org.hibernate.AnnotationException: Use of @OneToMany or @ManyToMany targeting an unmapped class:br.com.codefleck.tradebot.exchanges.trading.api.impl.MarketOrderBookImpl.sellOrders[br.com.codefleck.tradebot.tradingapi.MarketOrder]at org.hibernate.cfg.annotations.CollectionBinder.bindManyToManySecondPass(CollectionBinder.java:1136) at org.hibernate.cfg.annotations.CollectionBinder.bindStarToManySecondPass(CollectionBinder.java:792)
at org.hibernate.cfg.annotations.CollectionBinder$1.secondPass(CollectionBinder.java:727)
at org.hibernate.cfg.CollectionSecondPass.doSecondPass(CollectionSecondPass.java:70)
at org.hibernate.cfg.Configuration.originalSecondPassCompile(Configuration.java:1695)
at org.hibernate.cfg.Configuration.secondPassCompile(Configuration.java:1424)
at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1844)
at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl$4.perform(EntityManagerFactoryBuilderImpl.java:850) ... 66 more

在此先感谢您的帮助!

Answer 1

作为一个 PersistenceProvider 实现——比如 Hibernate——不能推断在这种情况下哪个具体类是“正确”的，你必须告诉 ORM 实现要使用什么类型在运行时。

在 JPA 2.1 specification 的第 11.1.40 节(PDF 第 474 页)中我们发现了一条与您的问题相关的重要信息:

The entity class that is the target of the association. Optional only if the collection-valued relationship property is defined using Java generics. Must be specified otherwise.

提示:

关于“OneToMany 注释元素”的表 37 列出了有关如何以编程方式为特定 OR 映射器声明运行时信息的更多详细信息。

鉴于上述信息，正确的方法是为 targetEntity 类型声明运行时相关信息:

@OneToMany(targetEntity= MarketOrderImpl.class) 
@JoinTable(name="marketorderimpl")
@MapKeyColumn(name="id")
private List<MarketOrder> sellOrders;

@OneToMany(targetEntity= MarketOrderImpl.class) 
@JoinTable(name="marketorderimpl")
@MapKeyColumn(name="id")
private List<MarketOrder> buyOrders;

希望对您有所帮助。