Hibernate composite key

有两种方法来map composite key. 第一种用@IdClass第二种用@Embeddable，参考链接： http://stackoverflow.com/questions/3585034/how-to-map-a-composite-key-with-hibernate 

一. @IdClass方法

1. Bean

package locationService.beans;

import java.io.Serializable;

import javax.persistence.*;

@Entity
@Table(name = "entity_to_entity")
@IdClass(EntityToEntityPk.class)
public class EntityToEntity implements Serializable {

	  private static final long serialVersionUID = 11L;
	  private int parentId;
	  private int childId;
	  
	  @Id
	  @Column(name="parent_id")
	  public int getParentId() {
		return parentId;
	  } 
	  public void setParentId(int parentId) {
		this.parentId = parentId;
	  }
	  
	  @Id
	  @Column(name="child_id")
	  public int getChildId() {
		return childId;
	  }
	  public void setChildId(int childId) {
		this.childId = childId;
	  }


	  @Override
	  public String toString() {
	    return "parentId is " + parentId + ", childId is " + childId;
	  }

}


class EntityToEntityPk implements Serializable {
	  private static final long serialVersionUID = 12L;
	  protected Integer parentId;
	  protected Integer childId;
	  
	  public EntityToEntityPk() {}
	  
	  public EntityToEntityPk(Integer parentId, Integer childId) {
		  this.parentId = parentId;
		  this.childId = childId;
	  }
	
	  public Integer getParentId() {
		return parentId;
	  } 
	  public void setParentId(int parentId) {
		this.parentId = parentId;
	  }
	  
	  public Integer getChildId() {
		return childId;
	  }
	  public void setChildId(int childId) {
		this.childId = childId;
	  }
	  
	  @Override
	  public boolean equals(Object o) {
	      if(o instanceof EntityToEntityPk){
	    	  EntityToEntityPk other = (EntityToEntityPk) o;
	          return parentId.equals(other.getParentId()) && childId.equals(other.getChildId());
	      }
	
	      return false;
	  }
	
	  @Override
	  public int hashCode() {
	      return parentId.hashCode() + childId.hashCode();
	  }
  

}

　　

注意equals和hasCode方法是composite key必须要有的

A composite id must implement both methods or the id will not work properly. Hibernate must be able to compare ids. A composite id will most likely use all its id fields in the equals and hashCode methods.

An entity does not need to implement equals and hashCode under some conditions. The persistence context guaranties that an entity with a given id exists only once. You cannot let two objects with the same id become persistent. Assuming that a class Country uses the isocode as ID, the following code will cause a non unique object exception.

参考链接： http://www.laliluna.de/jpa-hibernate-guide/ch06s06.html

2. Unit Test

  @Test
  public void testEnityToEntity() {
	 Session session = Config.getSessionFactory().openSession();
	 session.beginTransaction();
	
	 Query query = session.createQuery("select t.parentId from EntityToEntity t");
	
	 @SuppressWarnings("unchecked")
	 List<Object> entities = query.list();
	 assertEquals(entities.get(0), 1);
	 
	 session.getTransaction().commit();
	 session.close();
  }