使用 JPA 1.0 注释的派生复合密钥（复合密钥多对一）答案

【问题标题】：Derived Composite Key using JPA 1.0 Annotations (composite key-many-to-one)使用 JPA 1.0 注释的派生复合密钥（复合密钥多对一）
【发布时间】：2015-11-04 13:25:28
【问题描述】：

我有一个简单的关系，如上图所示。

我可以使用以下 Hibernate Mapping 来保持它：

<class name="Strategy" table="Strategy">
    <id name="id" column="StrategyId" unsaved-value="any">
        <generator class="identity"/>
    </id>
    <property name="status" column="Status"/>
</class>

<class name="Alert" table="Alert">
    <id name="id" column="AlertId">
        <generator class="identity"/>
    </id>
    <property name="name" column="Name"/>        
</class>

<class name="StrategyAlert" table="StrategyAlert">
    <composite-id>            
        <key-many-to-one name="strategy" class="Strategy" column="StrategyId"/>
        <key-many-to-one name="alert" class="Alert" column="AlertId"/>
    </composite-id>
    <property name="nominal" column="Nominal"/>
</class>

我很难弄清楚如何使用 JPA 1.0 中的注释来做到这一点。

这是我目前得到的：

警报类：

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

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="ALERTID")
    private int id;

    @Column(name="NAME")
    private String name;    
}

策略类：

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

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)    
    @Column(name="STRATEGYID")
    private int id;

    @Column(name="STATUS")
    private String status;
}

StrategyAlertPK 类：

public class StrategyAlertPK implements Serializable {

    private int strategyId;
    private int alertId;
}

StrategyAlert 类：

@Entity
@Table(name="STRATEGYALERT")
@IdClass(StrategyAlertPK.class)
public class StrategyAlert implements Serializable {

    @Id
    @Column(name="STRATEGYID")
    private int strategyId;

    @Id
    @Column(name="ALERTID")
    private int alertId;

    @ManyToOne
    @JoinColumn(name="STRATEGYID", insertable=false, updatable=false)
    private Strategy strategy;

    @ManyToOne
    @JoinColumn(name="ALERTID", insertable=false, updatable=false)
    private Alert alert;

    @Column
    private String nominal;
}

测试用例：

em.getTransaction().begin();       
Alert alert = new Alert();
alert.setName("NAME");
em.persist(alert);

Strategy strategy = new Strategy();
strategy.setStatus("STATUS");        
em.persist(strategy);

StrategyAlert strategyAlert = new StrategyAlert();
strategyAlert.setAlert(alert);
strategyAlert.setStrategy(strategy);
strategyAlert.setNominal("NOMINAL");
em.persist(strategyAlert);        
em.getTransaction().commit();

我收到以下错误：

参照完整性约束违规：“FK80432DA9CE00672E: PUBLIC.STRATEGYALERT FOREIGN KEY(STRATEGYID) REFERENCES PUBLIC.STRATEGY(STRATEGYID) (0)

我正在使用<property name="hibernate.hbm2ddl.auto" value="create" /> 来生成表格。

如何正确注释 StrategyAlert 类？

【问题讨论】：

标签： java hibernate jpa annotations

【解决方案1】：

看看这个问题：How to implement a complex many to many relationship in JPA?

我认为这里的问题是您必须加入 JPA 1 中描述的 Id 声明和 manyToOne 声明，我现在无法测试代码，但或多或少必须是这样的

@Entity
@Table(name="STRATEGYALERT")
@IdClass(StrategyAlertPK.class)
public class StrategyAlert implements Serializable {
   @Id
   @ManyToOne
   @JoinColumn(name="STRATEGYID", insertable=false, updatable=false)
   private Strategy strategy;

   @Id
   @ManyToOne
   @JoinColumn(name="ALERTID", insertable=false, updatable=false)
   private Alert alert;

   @Column
   private String nominal;

   // TODO Getters and setters
}

更新

嗨，

现在我可以测试代码，并且正在使用以下代码为 m 工作（一些未成年人更正）：

/**
 * 
 */
package hib;

import java.io.Serializable;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

/**
 *
 */
@Entity
@Table(name="ALERT")
public class Alert implements Serializable {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    @Column(name="ALERTID")
    private int id;

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

    /**
     * @return the id
     */
    public int getId() {
        return id;
    }

    /**
     * @param id the id to set
     */
    public void setId(int id) {
        this.id = id;
    }

    /**
     * @return the name
     */
    public String getName() {
        return name;
    }

    /**
     * @param name the name to set
     */
    public void setName(String name) {
        this.name = name;
    }
}

策略

/**
 * 
 */
package hib;

import java.io.Serializable;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

/**
 *
 */
@Entity
@Table(name="STRATEGY")
public class Strategy implements Serializable {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)    
    @Column(name="STRATEGYID")
    private int id;

    @Column(name="STATUS")
    private String status;

    /**
     * @return the id
     */
    public int getId() {
        return id;
    }

    /**
     * @param id the id to set
     */
    public void setId(int id) {
        this.id = id;
    }

    /**
     * @return the status
     */
    public String getStatus() {
        return status;
    }

    /**
     * @param status the status to set
     */
    public void setStatus(String status) {
        this.status = status;
    }
}

战略警报PK

/**
 * 
 */
package hib;

import java.io.Serializable;

import javax.persistence.Embeddable;

/**
 *
 */
@Embeddable
public class StrategyAlertPK implements Serializable {

    @ManyToOne
    private Strategy strategy;

    @ManyToOne
    private Alert alert;
    /**
     * @return the strategy
     */
    public Strategy getStrategy() {
        return strategy;
    }
    /**
     * @param strategy the strategy to set
     */
    public void setStrategy(Strategy strategy) {
        this.strategy = strategy;
    }
    /**
     * @return the alert
     */
    public Alert getAlert() {
        return alert;
    }
    /**
     * @param alert the alert to set
     */
    public void setAlert(Alert alert) {
        this.alert = alert;
    }

    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }

        if (o == null || getClass() != o.getClass()) {
            return false;
        }

        StrategyAlertPK that = (StrategyAlertPK) o;

        if (strategy != null ? !strategy.equals(that.strategy) : that.strategy != null) {
            return false;
        }
        if (alert != null ? !alert.equals(that.alert) : that.alert != null) {
            return false;
        }

        return true;
    }

    public int hashCode() {
        int result;
        result = (strategy != null ? strategy.hashCode() : 0);
        result = 31 * result + (alert != null ? alert.hashCode() : 0);
        return result;
    }


}

策略提示

/**
 * 
 */
package hib;

import java.io.Serializable;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.IdClass;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

/**
 *
 */
@Entity
@Table(name="STRATEGYALERT")
    @AssociationOverrides({ @AssociationOverride(name = "pk.strategy", joinColumns = @JoinColumn(name = "STRATEGYID")),
    @AssociationOverride(name = "pk.alert", joinColumns = @JoinColumn(name = "ALERTID")) })
public class StrategyAlert implements Serializable {

    @EmbeddedId
    private StrategyAlertPK pk = new StrategyAlertPK();

    @Column
    private String nominal;

    @Transient
    public Strategy getStrategy() {
        return pk.getStrategy();
    }

    public void setStrategy(Strategy strategy) {
        pk.setStrategy(strategy);
    }

    @Transient
    public Alert getAlert() {
        return pk.getAlert();
    }

    public void setAlert(Alert alert) {
        pk.setAlert(alert);
    }

    /**
     * @return the nominal
     */
    public String getNominal() {
        return nominal;
    }

    /**
     * @param nominal the nominal to set
     */
    public void setNominal(String nominal) {
        this.nominal = nominal;
    }
}

使用该代码，您的测试运行良好（我使用 JPA 1.0.1、Hibernate 3.3.1.GA 和 spring 2.5.5 对其进行了测试）。我使用 H2 作为内存数据库，所以我必须在生成的值中将 Identity 更改为 AUTO，也许你不需要这样做。

希望有所帮助！

【讨论】：

感谢弗朗西斯科的帮助我试过了，我收到一个错误，即 Id 类找不到它的属性：“无法在带有 @IdClass:hib 注释的实体中找到属性（alertId，strategyId）。战略警报”
我已经尝试了所有我能想到的方法，但我无法让它发挥作用。考虑到它在 XML 中是多么容易，您会认为使用 Annotations 应该很容易。有谁知道如何让它工作？
嗨，我更新了我的答案，现在我可以测试代码并为我工作。希望有帮助
我也在使用 H2。我复制/粘贴了您的代码，只是将包重命名为 hib。我收到以下错误：Caused by: org.hibernate.PropertyAccessException: could not set a field value by reflection setter of hib.StrategyAlertPK.alert 和 Caused by: java.lang.IllegalArgumentException: Can not set int field hib.StrategyAlertPK.alert to hib.Alert。我正在使用 HIbernate v3.2.4 我可能会尝试另一个版本，因为我不明白为什么会发生这种情况。
我尝试了最新版本的 Hibernate 我可以使用 - v3.3.1.GA / Annotations 3.4.0.GA / EntityManager 3.4.0.GA 并且我得到完全相同的错误：Can not set int field hib.StrategyAlertPK.alert to hib.Alert。我不知道下一步该尝试什么

【解决方案2】：

我找到了解决方案，但我认为这不是正确的方法。

我有一个用于 ID 的静态嵌套类。然后在这两种 setter 方法中，我还设置了 ID。这似乎是一种非常手动的方法，肯定有更好的方法吗？

@Entity
@Table(name="STRATEGYALERT")
public class StrategyAlert {

    @Embeddable
    public static class Id implements Serializable {
        private static final long serialVersionUID = -8270591004786497335L;

        @Column(name="STRATEGYID")
        private int strategyId;

        @Column(name="ALERTID")
        private int alertId;

        public Id() {}

        public Id(int strategyId, int alertId) {
            this.strategyId = strategyId;
            this.alertId = alertId;
        }

        @Override
        public int hashCode() {
            final int prime = 31;
            int result = 1;
            result = prime * result + alertId;
            result = prime * result + strategyId;
            return result;
        }

        @Override
        public boolean equals(Object obj) {
            if(this == obj)
                return true;
            if(obj == null)
                return false;
            if(getClass() != obj.getClass())
                return false;
            Id other = (Id)obj;
            if(alertId != other.alertId)
                return false;
            if(strategyId != other.strategyId)
                return false;
            return true;
        }

    }    

    @EmbeddedId
    private Id id = new Id();

    @ManyToOne
    @JoinColumn(name="STRATEGYID", insertable=false, updatable=false)
    private Strategy strategy;

    @ManyToOne
    @JoinColumn(name="ALERTID", insertable=false, updatable=false)
    private Alert alert;

    @Column(name="NOMINAL")
    private String nominal;    

    public StrategyAlert() {}

    public void setStrategy(Strategy strategy) {
        this.strategy = strategy;    
        // SET ID
        this.id.strategyId = strategy.getId();
    }

    public void setAlert(Alert alert) {
        this.alert = alert;    
        // SET ID
        this.id.alertId = alert.getId();
    }

    // Other Getters & Setters...
}

【讨论】：