hibernate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。

1. public class Category  {
2. private Integer id;
3. private String name;
4. private Category parentCategory; // 父类别
5. private Set<Category> childCategories = new HashSet<Category>(); // 子类别
6. // getter and setter
7. }

用XML映射

1. <hibernate-mapping package="org.monday.hibernate4.domain">
2. <class name="Category" table="tbl_category">
3. <id name="id">
4. <generator class="identity" />
5. </id>
6. <property name="name" />
7. <many-to-one name="parentCategory" class="Category" column="category_id" />
8. <set name="childCategories" inverse="true" cascade="all">
9. <key column="category_id" />
10. <one-to-many class="Category" />
11. </set>
12. </class>
13. </hibernate-mapping>

用@Annotation映射

1. @Entity
2. @Table(name = "tbl_category")
3. public class Category  {
4. @Id
5. @GeneratedValue(strategy = GenerationType.IDENTITY)
6. private Integer id;
7. private String name;
8. @ManyToOne
9. @JoinColumn(name = "category_id")
10. private Category parentCategory; // 父类别
11. @OneToMany(mappedBy = "parentCategory", targetEntity = Category.class, cascade = CascadeType.ALL)
12. private Set<Category> childCategories = new HashSet<Category>(); // 子类别
13. //getter and setter
14. }

测试代码

1. Category foodCategory = new Category("food");
2. Category fruitCategory = new Category("fruit");
3. Category vegetableCategory = new Category("vegetable");
4. Category appleCategory = new Category("apple");
5. Category orangeCategory = new Category("orange");
6. Category tomatoCategory = new Category("tomato");
7. // 建立食品类别和水果类别之间的关联关系
8. foodCategory.getChildCategories().add(fruitCategory);
9. fruitCategory.setParentCategory(foodCategory);
10. // 建立食品类别和蔬菜类别之间的关联关系
11. foodCategory.getChildCategories().add(vegetableCategory);
12. vegetableCategory.setParentCategory(foodCategory);
13. // 建立水果类别和苹果类别之间的关联关系
14. fruitCategory.getChildCategories().add(appleCategory);
15. appleCategory.setParentCategory(fruitCategory);
16. // 建立水果类别和桔子类别之间的关联关系
17. fruitCategory.getChildCategories().add(orangeCategory);
18. orangeCategory.setParentCategory(fruitCategory);
19. // 建立西红柿类别和蔬菜类别之间的关联关系
20. tomatoCategory.setParentCategory(vegetableCategory);
21. vegetableCategory.getChildCategories().add(tomatoCategory);
22. session.save(foodCategory);

SQL schema

1. Hibernate:
2. create table CATEGORYS (
3. id integer not null,
4. name varchar(255),
5. category_id bigint,
6. primary key (id)
7. )
8. Hibernate:
9. alter table CATEGORYS
10. add index FK36CF3159B3B4FFA (category_id),
11. add constraint FK36CF3159B3B4FFA
12. foreign key (category_id)
13. references CATEGORYS (id)

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

1.改进实体类

1. @Entity
2. @Table(name = "tbl_category")
3. public class Category {
4. @Id
5. @GeneratedValue(strategy = GenerationType.IDENTITY)
6. private Integer id;
7. private String name;
8. @ManyToOne
9. @JoinColumn(name = "category_id")
10. private Category parentCategory; // 父类别
11. @OneToMany(mappedBy = "parentCategory", targetEntity = Category.class, cascade = CascadeType.ALL)
12. private Set<Category> childCategories = new HashSet<Category>(); // 子类别
13. //getter and setter
14. /** 添加子类别 */
15. public void addChildCategory(Category category) {
16. if (category == null) {
17. throw new IllegalArgumentException("Can't add a null Category as child.");
18. }
19. // 删除旧的父类别Category
20. if (category.getParentCategory() != null) {
21. category.getParentCategory().getChildCategories().remove(category);
22. }
23. // 设置新的父类别Category
24. category.setParentCategory(this);
25. // 向当前Category对象中加入子类别
26. this.getChildCategories().add(category);
27. }
28. }

2.测试代码

1. // 建立食品类别和水果类别之间的关联关系
2. foodCategory.addChildCategory(fruitCategory);
3. // 建立食品类别和蔬菜类别之间的关联关系
4. foodCategory.addChildCategory(vegetableCategory);
5. // 建立水果类别和苹果类别之间的关联关系
6. fruitCategory.addChildCategory(appleCategory);
7. // 建立水果类别和桔子类别之间的关联关系
8. fruitCategory.addChildCategory(orangeCategory);
9. // 建立西红柿类别和蔬菜类别之间的关联关系
10. vegetableCategory.addChildCategory(tomatoCategory);
11. session.save(foodCategory);