文章目录
-
- 添加依赖
- 构建Entity
- 构建Repository
- 构建初始数据
- 测试
Spring Boot JPA中关联表的使用
本文中，我们会将会通过一个Book和Category的关联关系，来讲解如何在JPA中使用。
我们还是使用H2内存数据库来做测试：
<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-data-jpa</artifactId></dependency><dependency><groupId>com.h2database</groupId><artifactId>h2</artifactId><scope>runtime</scope></dependency>
构建Entity
下面我们构建两个Entity：
@Data@Entitypublic class Book {@Id@GeneratedValue(strategy = GenerationType.IDENTITY)private Long id;private String title;@ManyToOneprivate Category category;}
@Data@Entitypublic class Category {@Id@GeneratedValue(strategy = GenerationType.IDENTITY)private Long id;private String name;@OneToMany(mappedBy = "category", cascade = CascadeType.ALL)private List<Book> books;}
上面我们定义了两个Entity，Category和Book是一对多的关系。我们通过@ManyToOne和@OneToMany来定义相应的关系。
构建Repository
我们接下来构建相应的Repository：
public interface BookRepository extends CrudRepository<Book, Long> {long deleteByTitle(String title);@Modifying@Query("delete from Book b where b.title=:title")void deleteBooks(@Param("title") String title);}
public interface CategoryRepository extends CrudRepository<Category, Long> {}
构建初始数据
为了方便测试，我们先构建需要的数据schema.sql和data.sql:
CREATE TABLE book (id BIGINT NOT NULL AUTO_INCREMENT,title VARCHAR(128) NOT NULL,category_id BIGINT,PRIMARY KEY (id));CREATE TABLE category (id BIGINT NOT NULL AUTO_INCREMENT,name VARCHAR(128) NOT NULL,PRIMARY KEY (id));
insert into book(id,title,category_id)values(1,'The Hobbit',1);insert into book(id,title,category_id)values(2,'The Rabbit',1);insert into category(id,name)values(1,'category');
测试
我们看一下怎么从Book中删除一条数据：
@Testpublic void whenDeleteByIdFromRepository_thenDeletingShouldBeSuccessful() {assertThat(bookRepository.count()).isEqualTo(2);bookRepository.deleteById(1L);assertThat(bookRepository.count()).isEqualTo(1);}
再看一下category的删除：
@Testpublic void whenDeletingCategories_thenBooksShouldAlsoBeDeleted() {categoryRepository.deleteAll();assertThat(bookRepository.count()).isEqualTo(0);assertThat(categoryRepository.count()).isEqualTo(0);}
再看一下book的删除：
@Testpublic void whenDeletingBooks_thenCategoriesShouldAlsoBeDeleted() {bookRepository.deleteAll();assertThat(bookRepository.count()).isEqualTo(0);assertThat(categoryRepository.count()).isEqualTo(1);}
因为我们只在Category中指定了cascade = CascadeType.ALL， 所以删除category的时候可以删除相关联的Book，但是删除Book的时候不会删除相关联的category。