Spring-Data-JPA 定义实体类关系:多对多(增删改查)

秒速五厘米 2023-10-10 11:32 26阅读 0赞

## Spring-Data-JPA 关系描述（多对多）　 ##

实体Book：书籍。

实体Author：作者。

书籍和作者是多对多的关系。一本书籍可以由很多的作者编写，一个作者也可以编写写很多本书。

JPA中使用@ManyToMany来注解多对多的关系，由一个关联表来维护。这个关联表的表名默认是：主表名+下划线+从表名。(主表是指关系维护端对应的表,从表指关系被维护端对应的表)。这个关联表只有两个外键字段，分别指向主表ID和从表ID。字段的名称默认为：主表名+下划线+主表中的主键列名，从表名+下划线+从表中的主键列名。

需要注意的：

1、多对多关系中一般不设置级联保存、级联删除、级联更新等操作。

2、可以随意指定一方为关系维护端，在这个例子中，我指定Book为关系维护端，所以生成的关联表名称为： book\_author，关联表的字段为：book\_id和author\_id。

3、多对多关系的绑定由关系维护端来完成，即由Book.setAuthors(authors)来绑定多对多的关系。关系被维护端不能绑定关系，即Author不能绑定关系。

4、多对多关系的解除由关系维护端来完成，即由Book.getAuthors.remove(author)来解除多对多的关系。关系被维护端不能解除关系，即Author不能解除关系。

5、如果Book和Author已经绑定了多对多的关系，那么不能直接删除Author，需要由Book解除关系后，才能删除Author。但是可以直接删除Book，因为Book是关系维护端，删除Book时，会先解除Book和Author的关系，再删除Author。

## Spring-Data-JPA 源码 ##

### 实体对象和Dao层 ###

package com.zzg.entity;
    
    import java.io.Serializable;
    import java.util.HashSet;
    import java.util.Set;
    
    import javax.persistence.CascadeType;
    import javax.persistence.Column;
    import javax.persistence.Entity;
    import javax.persistence.GeneratedValue;
    import javax.persistence.Id;
    import javax.persistence.JoinColumn;
    import javax.persistence.JoinTable;
    import javax.persistence.ManyToMany;
    import javax.persistence.Table;
    
    @SuppressWarnings("serial")
    @Entity
    @Table(name="book")
    public class Book implements Serializable {
    	@Id
        @GeneratedValue
        private Long id;
    	
    	@Column(name="name")
        private String name;
    
        @ManyToMany(cascade = CascadeType.ALL)
        @JoinTable(name = "book_author", joinColumns = {
                @JoinColumn(name = "book_id", referencedColumnName = "id")}, inverseJoinColumns = {
                @JoinColumn(name = "author_id", referencedColumnName = "id")})
        private Set<Author> authors;
    
        public Book() {
            super();
        }
    
        public Book(String name) {
            super();
            this.name = name;
            this.authors = new HashSet<>();
        }
    
        public Book(String name, Set<Author> authors) {
            super();
            this.name = name;
            this.authors = authors;
        }
    
        public Long getId() {
            return id;
        }
    
        public void setId(Long id) {
            this.id = id;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public Set<Author> getAuthors() {
            return authors;
        }
    
        public void setAuthors(Set<Author> authors) {
            this.authors = authors;
        }
    
        @Override
        public String toString() {
            return String.format("Book [id=%s, name=%s, authors=%s]", id, name, authors);
        }
    }

package com.zzg.entity;
    
    import java.io.Serializable;
    import java.util.Set;
    
    import javax.persistence.Column;
    import javax.persistence.Entity;
    import javax.persistence.GeneratedValue;
    import javax.persistence.Id;
    import javax.persistence.ManyToMany;
    import javax.persistence.Table;
    
    @SuppressWarnings("serial")
    @Entity
    @Table(name="author")
    public class Author implements Serializable {
    	@Id
        @GeneratedValue
        private Long id;
    
    	@Column(name="name")
        private String name;
    
        @ManyToMany(mappedBy = "authors")
        private Set<Book> books;
    
        public Author() {
            super();
        }
    
        public Author(String name) {
            super();
            this.name = name;
        }
    
        public Long getId() {
            return id;
        }
    
        public void setId(Long id) {
            this.id = id;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public Set<Book> getBooks() {
            return books;
        }
    
        public void setBooks(Set<Book> books) {
            this.books = books;
        }
    
        @Override
        public String toString() {
            return String.format("Author [id=%s, name=%s, books=%s]", id, name, books);
        }
    }

package com.zzg.entity.dao;
    
    import org.springframework.data.jpa.repository.JpaRepository;
    
    import com.zzg.entity.Author;
    
    public interface AuthorRepository extends JpaRepository<Author, Long> {
    
    }

package com.zzg.entity.dao;
    
    import org.springframework.data.jpa.repository.JpaRepository;
    
    import com.zzg.entity.Book;
    
    public interface BookRepository extends JpaRepository<Book, Long> {
    
    }

### 功能测试(test)定义: ###

package com.zzg.test;
    
    import java.util.Arrays;
    import java.util.Set;
    
    import org.junit.Test;
    import org.junit.runner.RunWith;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.boot.test.context.SpringBootTest;
    import org.springframework.test.context.junit4.SpringRunner;
    
    import com.zzg.entity.Author;
    import com.zzg.entity.Book;
    import com.zzg.entity.dao.AuthorRepository;
    import com.zzg.entity.dao.BookRepository;
    
    @RunWith(SpringRunner.class)
    @SpringBootTest
    public class ManyToManyTest {
    
    	
    	@Autowired
    	private AuthorRepository authorRepository;
    	
    	@Autowired
    	private BookRepository bookRepository;
    	
    	@Test
    	public void insertManyToMany() {
    		
    		Author lewis = new Author("Lewis");
            Author mark = new Author("Mark");
            Author peter = new Author("Peter");
    
            Book spring = new Book("Spring in Action");
            spring.getAuthors().addAll(Arrays.asList(lewis, mark));
    
            Book springboot = new Book("Spring Boot in Action");
            springboot.getAuthors().addAll(Arrays.asList(lewis, peter));
    
            bookRepository.save(Arrays.asList(spring, springboot));
    		
    	}
    	
    	@Test
    	public void selectManyToMany() {
    		Book book = bookRepository.findOne(1L);
    		System.out.println(book.toString());
    		
    		book.getAuthors().stream().forEach(item->{
    			System.out.println(item.toString());
    		});
    		
    		
    	}
    	
    	@Test
    	public void updateManyToMany() {
    		// 移除目标数据
    		Author author = authorRepository.findOne(1L);
    		// 查询指定数据
    		Book book = bookRepository.findOne(1L);
    		System.out.println(book.toString());
    		// 数据移除
    		book.getAuthors().add(new Author("zzg"));
    		// 数据保存
    		bookRepository.save(book);
    		
    		
    	}
    	
    	@Test
    	public void deleteManyToMany() {
    		bookRepository.delete(1L);
    	}
    
    
    }

效果截图：

新增

![20200910005849555.png][]

修改

![20200910005906947.png][]

删除

![20200910005920164.png][]

查询

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3pob3V6aGl3ZW5nYW5n_size_16_color_FFFFFF_t_70][]

### 建库脚本： ###

CREATE TABLE IF NOT EXISTS `author` (
      `id` bigint(10) NOT NULL AUTO_INCREMENT,
      `name` varchar(32) NOT NULL DEFAULT '0',
      PRIMARY KEY (`id`)
    ) ENGINE=InnoDB AUTO_INCREMENT=11 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
    
    
    -- 导出  表 oasys.book 结构
    CREATE TABLE IF NOT EXISTS `book` (
      `id` bigint(10) NOT NULL AUTO_INCREMENT,
      `name` varchar(32) NOT NULL DEFAULT '0',
      PRIMARY KEY (`id`)
    ) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
    
    
    
    -- 导出  表 oasys.book_author 结构
    CREATE TABLE IF NOT EXISTS `book_author` (
      `book_id` bigint(10) NOT NULL,
      `author_id` bigint(10) NOT NULL,
      KEY `author_id` (`author_id`),
      KEY `book_id` (`book_id`),
      CONSTRAINT `author_id` FOREIGN KEY (`author_id`) REFERENCES `author` (`id`),
      CONSTRAINT `book_id` FOREIGN KEY (`book_id`) REFERENCES `book` (`id`)
    ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;

[20200910005849555.png]: https://img-blog.csdnimg.cn/20200910005849555.png
[20200910005906947.png]: https://img-blog.csdnimg.cn/20200910005906947.png
[20200910005920164.png]: https://img-blog.csdnimg.cn/20200910005920164.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3pob3V6aGl3ZW5nYW5n_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20200910005956197.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3pob3V6aGl3ZW5nYW5n,size_16,color_FFFFFF,t_70