JPA自连接例子

public class ProductType implements Serializable{
	private static final long serialVersionUID = 8106351120886053881L;
	/** 类别id **/
	private Integer typeid;
	/** 类别名称 **/
	private String name;
	/** 子类别 **/
	private Set<ProductType> childtypes = new HashSet<ProductType>();
	/** 所属父类 **/
	private ProductType parent;
	
	private Set<ProductInfo> products = new HashSet<ProductInfo>();
	
	@OneToMany(mappedBy="type", cascade=CascadeType.REMOVE)
	public Set<ProductInfo> getProducts() {
		return products;
	}

	public void setProducts(Set<ProductInfo> products) {
		this.products = products;
	}

	public ProductType() {}
	
	public ProductType(Integer typeid) {
		this.typeid = typeid;
	}

	public ProductType(String name, String note) {
		this.name = name;
		this.note = note;
	}
	@ManyToOne(cascade=CascadeType.REFRESH)
	@JoinColumn(name="parentid")
	public ProductType getParent() {
		return parent;
	}

	public void setParent(ProductType parent) {
		this.parent = parent;
	}
	@OneToMany(cascade={CascadeType.REFRESH,CascadeType.REMOVE},mappedBy="parent")
	public Set<ProductType> getChildtypes() {
		return childtypes;
	}

	public void setChildtypes(Set<ProductType> childtypes) {
		this.childtypes = childtypes;
	}

	@Column(length=36,nullable=false)
	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}


	@Id @GeneratedValue(strategy=GenerationType.AUTO)
	public Integer getTypeid() {
		return typeid;
	}

	public void setTypeid(Integer typeid) {
		this.typeid = typeid;
	}

	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + ((typeid == null) ? 0 : typeid.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;
		final ProductType other = (ProductType) obj;
		if (typeid == null) {
			if (other.typeid != null)
				return false;
		} else if (!typeid.equals(other.typeid))
			return false;
		return true;
	}
}