使用JPA雙向多對多關聯關係@ManyToMany

package com.jpa.helloworld; 
import java.util.HashSet;
import java.util.Set;
 
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
import javax.persistence.Table;
 
@Table(name="CATEGORYS")
@Entity
public class Category { 
	private Integer cID; 
	private String cName; 
	private Set<Item> items = new HashSet<Item>();
 
	@Id
	@Column(name="C_ID")
	@GeneratedValue
	public Integer getcID() {
		return cID;
	}
 
	public void setcID(Integer cID) {
		this.cID = cID;
	}
 
	@Column(name="C_NAME")
	public String getcName() {
		return cName;
	}
 
	public void setcName(String cName) {
		this.cName = cName;
	}
	
	//新增了mappedBy屬性則不能使用@JoinTable註解
	@ManyToMany(mappedBy="categorys")
	public Set<Item> getItems() {
		return items;
	}
 
	public void setItems(Set<Item> items) {
		this.items = items;
	} 
}

package com.jpa.helloworld; 
import java.util.HashSet;
import java.util.Set;
 
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.Table;
 
@Table(name="ITEMS")
@Entity
public class Item { 
	private Integer iId; 
	private String iName; 
	private Set<Category> categorys = new HashSet<Category>();
 
	@Id
	@GeneratedValue
	@Column(name="I_ID")
	public Integer getiId() {
		return iId;
	}
 
	public void setiId(Integer iId) {
		this.iId = iId;
	}
 
	@Column(name="I_NAME")
	public String getiName() {
		return iName;
	}
 
	public void setiName(String iName) {
		this.iName = iName;
	}
 
	//使用@JoinTable註解新增中間表
	//其中name屬性設定中間表的表名
	//joinCloums屬性在中間表中新增的列
	//JoinColumns屬性：
	//				@joinColumn屬性設定中間表中的列名
	//						referencedColumnName屬性指向被對映表的主鍵（可以沒有該屬性）
	//@inverseJoinColumns另外一張表在中間表中的列
	@JoinTable(
			name="ITEMS_CATEGORYS",
//			joinColumns = {@JoinColumn(name="ITEM_ID",referencedColumnName="I_ID")},
			joinColumns = {@JoinColumn(name="ITEM_ID")},
//			inverseJoinColumns= {@JoinColumn(name="CATEGORY_ID", referencedColumnName="C_ID")})
			inverseJoinColumns= {@JoinColumn(name="CATEGORY_ID")})
	@ManyToMany
	public Set<Category> getCategorys() {
		return categorys;
	}
 
	public void setCategorys(Set<Category> categorys) {
		this.categorys = categorys;
	} 
}