示例：一個類別（Category）下面有多個子類別，多個子類別屬于同一個父類別。

Java代碼 ?

public?class?Category??{??

??

????private?Integer?id;??

????private?String?name;??

????private?Category?parentCategory;?//?父類別??

????private?Set<Category>?childCategories?=?new?HashSet<Category>();?//?子類別??

??

????//?getter?and?setter??

}??

?用XML映射

Xml代碼 ?

<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

?

Java代碼 ?

@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;?//?父類別??

??

????@OneToMany(mappedBy?=?"parentCategory",?targetEntity?=?Category.class,?cascade?=?CascadeType.ALL)??

????private?Set<Category>?childCategories?=?new?HashSet<Category>();?//?子類別??

??

????//getter?and?setter??

}??

?

測試代碼

Java代碼 ?

?????????????????????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");??

??

//?建立食品類別和水果類別之間的關(guān)聯(lián)關(guān)系??

foodCategory.getChildCategories().add(fruitCategory);??

fruitCategory.setParentCategory(foodCategory);??

??

//?建立食品類別和蔬菜類別之間的關(guān)聯(lián)關(guān)系??

foodCategory.getChildCategories().add(vegetableCategory);??

vegetableCategory.setParentCategory(foodCategory);??

??

//?建立水果類別和蘋果類別之間的關(guān)聯(lián)關(guān)系??

fruitCategory.getChildCategories().add(appleCategory);??

appleCategory.setParentCategory(fruitCategory);??

??

//?建立水果類別和桔子類別之間的關(guān)聯(lián)關(guān)系??

fruitCategory.getChildCategories().add(orangeCategory);??

orangeCategory.setParentCategory(fruitCategory);??

??

//?建立西紅柿類別和蔬菜類別之間的關(guān)聯(lián)關(guān)系??

tomatoCategory.setParentCategory(vegetableCategory);??

vegetableCategory.getChildCategories().add(tomatoCategory);??

??

session.save(foodCategory);??

?SQL schema

Sql代碼 ?

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)??

?

-----------------------------改進代碼---------------------------

?

1.改進實體類

Java代碼 ?

@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;?//?父類別??

??

????@OneToMany(mappedBy?=?"parentCategory",?targetEntity?=?Category.class,?cascade?=?CascadeType.ALL)??

????private?Set<Category>?childCategories?=?new?HashSet<Category>();?//?子類別??

??

????//getter?and?setter??

??

????/**?添加子類別?*/??

????public?void?addChildCategory(Category?category)?{??

????????if?(category?==?null)?{??

????????????throw?new?IllegalArgumentException("Can't?add?a?null?Category?as?child.");??

????????}??

????????//?刪除舊的父類別Category??

????????if?(category.getParentCategory()?!=?null)?{??

????????????category.getParentCategory().getChildCategories().remove(category);??

????????}??

????????//?設(shè)置新的父類別Category??

????????category.setParentCategory(this);??

????????//?向當(dāng)前Category對象中加入子類別??

????????this.getChildCategories().add(category);??

????}??

}??

?

2.測試代碼

Java代碼 ?

//?建立食品類別和水果類別之間的關(guān)聯(lián)關(guān)系??

????????????foodCategory.addChildCategory(fruitCategory);??

??

????????????//?建立食品類別和蔬菜類別之間的關(guān)聯(lián)關(guān)系??

????????????foodCategory.addChildCategory(vegetableCategory);??

??

????????????//?建立水果類別和蘋果類別之間的關(guān)聯(lián)關(guān)系??

????????????fruitCategory.addChildCategory(appleCategory);??

??

????????????//?建立水果類別和桔子類別之間的關(guān)聯(lián)關(guān)系??

????????????fruitCategory.addChildCategory(orangeCategory);??

??

????????????//?建立西紅柿類別和蔬菜類別之間的關(guān)聯(lián)關(guān)系??

????????????vegetableCategory.addChildCategory(tomatoCategory);??

??

????????????session.save(foodCategory);??

?

?

?

?

?

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