Hibernate4一对多关系映射（自身关联）

示例：一个类别（Category）下面有多个子类别，多个子类别属于同一个父类别。

public class Category  {

	private Integer id;
	private String name;
	private Category parentCategory; // 父类别
	private Set<Category> childCategories = new HashSet<Category>(); // 子类别

	// getter and setter
}

 用XML映射

<hibernate-mapping package="org.monday.hibernate4.domain">
	<class name="Category" table="tbl_category">
		<id name="id">
			<generator class="identity" />
		</id>
		<property name="name" />
		<many-to-one name="parentCategory" class="Category" column="category_id" />
		<set name="childCategories" inverse="true" cascade="all">
			<key column="category_id" />
			<one-to-many class="Category" />
		</set>
	</class>
</hibernate-mapping>

 用@Annotation映射

 

@Entity
@Table(name = "tbl_category")
public class Category  {

	@Id
	@GeneratedValue(strategy = GenerationType.IDENTITY)
	private Integer id;
	private String name;

	@ManyToOne
	@JoinColumn(name = "category_id")
	private Category parentCategory; // 父类别

	@OneToMany(mappedBy = "parentCategory", targetEntity = Category.class, cascade = CascadeType.ALL)
	private Set<Category> childCategories = new HashSet<Category>(); // 子类别

	//getter and setter
}

 

测试代码

                        Category foodCategory = new Category("food");
			Category fruitCategory = new Category("fruit");
			Category vegetableCategory = new Category("vegetable");
			Category appleCategory = new Category("apple");
			Category orangeCategory = new Category("orange");
			Category tomatoCategory = new Category("tomato");

			// 建立食品类别和水果类别之间的关联关系
			foodCategory.getChildCategories().add(fruitCategory);
			fruitCategory.setParentCategory(foodCategory);

			// 建立食品类别和蔬菜类别之间的关联关系
			foodCategory.getChildCategories().add(vegetableCategory);
			vegetableCategory.setParentCategory(foodCategory);

			// 建立水果类别和苹果类别之间的关联关系
			fruitCategory.getChildCategories().add(appleCategory);
			appleCategory.setParentCategory(fruitCategory);

			// 建立水果类别和桔子类别之间的关联关系
			fruitCategory.getChildCategories().add(orangeCategory);
			orangeCategory.setParentCategory(fruitCategory);

			// 建立西红柿类别和蔬菜类别之间的关联关系
			tomatoCategory.setParentCategory(vegetableCategory);
			vegetableCategory.getChildCategories().add(tomatoCategory);

			session.save(foodCategory);

 SQL schema

Hibernate: 
    create table CATEGORYS (
        id integer not null,
        name varchar(255),
        category_id bigint,
        primary key (id)
    )
Hibernate: 
    alter table CATEGORYS 
        add index FK36CF3159B3B4FFA (category_id), 
        add constraint FK36CF3159B3B4FFA 
        foreign key (category_id) 
        references CATEGORYS (id)

 

-----------------------------改进代码---------------------------

 

1.改进实体类

@Entity
@Table(name = "tbl_category")
public class Category {

	@Id
	@GeneratedValue(strategy = GenerationType.IDENTITY)
	private Integer id;
	private String name;

	@ManyToOne
	@JoinColumn(name = "category_id")
	private Category parentCategory; // 父类别

	@OneToMany(mappedBy = "parentCategory", targetEntity = Category.class, cascade = CascadeType.ALL)
	private Set<Category> childCategories = new HashSet<Category>(); // 子类别

	//getter and setter

	/** 添加子类别 */
	public void addChildCategory(Category category) {
		if (category == null) {
			throw new IllegalArgumentException("Can't add a null Category as child.");
		}
		// 删除旧的父类别Category
		if (category.getParentCategory() != null) {
			category.getParentCategory().getChildCategories().remove(category);
		}
		// 设置新的父类别Category
		category.setParentCategory(this);
		// 向当前Category对象中加入子类别
		this.getChildCategories().add(category);
	}
}

 

2.测试代码

// 建立食品类别和水果类别之间的关联关系
			foodCategory.addChildCategory(fruitCategory);

			// 建立食品类别和蔬菜类别之间的关联关系
			foodCategory.addChildCategory(vegetableCategory);

			// 建立水果类别和苹果类别之间的关联关系
			fruitCategory.addChildCategory(appleCategory);

			// 建立水果类别和桔子类别之间的关联关系
			fruitCategory.addChildCategory(orangeCategory);

			// 建立西红柿类别和蔬菜类别之间的关联关系
			vegetableCategory.addChildCategory(tomatoCategory);

			session.save(foodCategory);