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。

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);