How to Use Hibernate for Composite Ids with association mappings

Recently, We faced a tricky situation with hibernate association mapping with a composite id field. We needed to have bidirectional association with one-to-may and many-to-one.Our tow tables was "REPORT" and "REPORT_SUMMARY" which has one-to-many relationship from REPORT to REPORT_SUMMARY and many-to-one relationship from REPORT_SUMMARY to REPORT table. The primary key of REPORT_SUMMARY table is defined as a composite primary key which consists of auto increment id field and the primary key of REPORT table.

CREATE TABLE REPORT (
     ID INT(10) NOT NULL AUTO_INCREMENT,
     NAME VARCHAR(45) NOT NULL,
     PRIMARY KEY (`ID`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

CREATE TABLE REPORT_SUMMARY (
   ID INT(10) NOT NULL AUTO_INCREMENT,
   NAME VARCHAR(45) NOT NULL,
   RPT_ID INT(10) NOT NULL,
   PRIMARY KEY (`ID`,`RPT_ID`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

The hibernate entity classes are as fallows.

Report.java

package com.semika.autoac.entities;

import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;
public class Report implements Serializable{

    private static final long serialVersionUID = 9146156921169669644L;

    private Integer id;
    private String name;
    private Set<ReportSummary> reportSummaryList  = new HashSet<ReportSummary>();
    
    public Integer getId() {
         return id;
    }
    public void setId(Integer id) {
         this.id = id;
    }
    public String getName() {
         return name;
    }
    public void setName(String name) {
         this.name = name;
    }
    public Set<ReportSummary> getReportSummaryList() {
         return reportSummaryList;
    }
    public void setReportSummaryList(Set<ReportSummary> reportSummaryList) {
         this.reportSummaryList = reportSummaryList;
    }
}

ReportSummary.java

package com.semika.autoac.entities;

import java.io.Serializable;
public class ReportSummary implements Serializable {

private static final long serialVersionUID = 8052962961003467437L;

private ReportSummaryId id;
private String name;

public ReportSummaryId getId() {
    return id;
}
public void setId(ReportSummaryId id) {
    this.id = id;
}
public String getName() {
    return name;
}
public void setName(String name) {
    this.name = name;
}
@Override
public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + ((id == null) ? 0 : id.hashCode());
    result = prime * result + ((name == null) ? 0 : name.hashCode());
    return result;
}
@Override
public boolean equals(Object obj) {
    if (this == obj)
        return true;
    if (obj == null)
        return false;
    if (getClass() != obj.getClass())
        return false;
    ReportSummary other = (ReportSummary) obj;
    if (id == null) {
       if (other.id != null)
          return false;
       } else if (!id.equals(other.id))
          return false;
    if (name == null) {
       if (other.name != null)
          return false;
       } else if (!name.equals(other.name))
          return false;

   return true;
  }
}

ReportSummaryId.java

package com.semika.autoac.entities;

import java.io.Serializable;

public class ReportSummaryId implements Serializable{

private static final long serialVersionUID = 6911616314813390449L;

private Integer id;
private Report report;

public Integer getId() {
   return id;
}
public void setId(Integer id) {
   this.id = id;
}
public Report getReport() {
   return report;
}
public void setReport(Report report) {
   this.report = report;
}
@Override
public int hashCode() {
   final int prime = 31;
   int result = 1;
   result = prime * result + ((id == null) ? 0 : id.hashCode());
   result = prime * result + ((report == null) ? 0 : report.hashCode());
   return result;
}
@Override
public boolean equals(Object obj) {
   if (this == obj)
      return true;
   if (obj == null)
      return false;
   if (getClass() != obj.getClass())
      return false;
   ReportSummaryId other = (ReportSummaryId) obj;
   if (id == null) {
      if (other.id != null)
         return false;
      } else if (!id.equals(other.id))
         return false;
   if (report == null) {
      if (other.report != null)
         return false;
      } else if (!report.equals(other.report))
         return false;

   return true;
  }
}

Report object has a collection of ReportSummary objects and ReportSummaryId has a reference to Report object. The most important part of this implementation is hibernate mapping files.

Report.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="com.semika.autoac.entities.Report" table="REPORT" >
         <id name="id" type="int" column="id" >
                 <generator class="native"/>
         </id>
         <property name="name">
               <column name="NAME" />
         </property>
         <set name="reportSummaryList" table="REPORT_SUMMARY" cascade="all" inverse="true">
             <key column="RPT_ID" not-null="true"></key>
             <one-to-many class="com.semika.autoac.entities.ReportSummary"/>
         </set>
     </class>
</hibernate-mapping>

ReportSummary.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
    <class name="com.semika.autoac.entities.ReportSummary" table="REPORT_SUMMARY" >
        <composite-id name="id" class="com.semika.autoac.entities.ReportSummaryId">
             <key-property name="id" column="ID"></key-property>
             <key-many-to-one name="report" 
                              class="com.semika.autoac.entities.Report"
                              column="RPT_ID"</key-many-to-one>
        </composite-id>
        <property name="name">
             <column name="NAME" />
        </property>
    </class>
</hibernate-mapping>