spring data jpa关联查询（一对一、一对多、多对多）

　　在实际过往的项目中，常用的查询操作有：1、单表查询，2、一对一查询（主表和详情表）3、一对多查询（一张主表，多张子表）4、多对多查询（如权限控制，用户、角色多对多）。做个总结，所以废话不多说。

　　使用idea构建springboot项目，引入依赖如下：

dependencies>
        <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>

<dependency>

<groupId>org.projectlombok</groupId>

<artifactId>lombok</artifactId>

<optional>true</optional>

</dependency>

<dependency>

<groupId>org.springframework.boot</groupId>

<artifactId>spring-boot-starter-test</artifactId>

<scope>test</scope>

</dependency>

</dependencies>

　　使用h2数据库做测试用，application.yml配置如下：

spring:
  jpa:
    generate-ddl: true
    hibernate:
      ddl-auto: update
    properties:
      hibenate:
        format_sql: false
    show-sql: true

　　首先，一对一有好几种，这里举例的是常用的一对一双向外键关联（改造成单向很简单，在对应的实体类去掉要关联其它实体的属性即可），并且配置了级联删除和添加，相关类如下：

package io.powerx;
import lombok.*;
import javax.persistence.*;
/**


Created by Administrator on 2018/8/15.

*/

@Getter

@Setter

@Entity

public class Book {

@Id

@GeneratedValue

private Integer id;
private String name;
@OneToOne(cascade = {CascadeType.PERSIST,CascadeType.REMOVE})

@JoinColumn(name="detailId",referencedColumnName = "id")

private BookDetail bookDetail;
public Book(){

super();

}

public Book(String name){

super();

this.name =name;

}
public Book(String name, BookDetail bookDetail) {

super();

this.name = name;

this.bookDetail = bookDetail;

}

@Override

public String toString() {

if (null == bookDetail) {

return String.format("Book [id=%s, name=%s, number of pages=%s]", id, name, "<EMPTY>");

}
return String.format("Book [id=%s, name=%s, number of pages=%s]", id, name, bookDetail.getNumberOfPages());

}

}

package io.powerx;
import lombok.Getter;

import lombok.Setter;
import javax.persistence.*;
@Getter

@Setter

@Entity(name = "BOOK_DETAIL")

public class BookDetail {
@Id

@GeneratedValue

private Integer id;
@Column(name = "NUMBER_OF_PAGES")

private Integer numberOfPages;
@OneToOne(mappedBy = "bookDetail")

private Book book;
public BookDetail() {

super();

}
public BookDetail(Integer numberOfPages) {

super();

this.numberOfPages = numberOfPages;

}
@Override

public String toString() {

if (null == book) {

return String.format("Book [id=%s, name=%s, number of pages=%s]", id, "<EMPTY>");

}
return String.format("Book [id=%s, name=%s, number of pages=%s]", id,book.getId(),book.getName());

}

}

package io.powerx;
import org.springframework.data.jpa.repository.JpaRepository;
/**

Created by Administrator on 2018/8/15.

*/

public interface BookRepository extends JpaRepository<Book,Integer> {

Book findByName(String name);

}

package io.powerx;
import org.springframework.data.jpa.repository.JpaRepository;
/**


Created by Administrator on 2018/8/15.

*/

public interface BookDetailRepository  extends JpaRepository<BookDetail, Integer>{
BookDetail findByNumberOfPages(Integer numberOfPages);

}

package io.powerx;
import org.junit.After;

import org.junit.Before;

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 java.util.Arrays;
import static org.junit.Assert.assertThat;
@RunWith(SpringRunner.class)

@SpringBootTest

public class OnetooneApplicationTests {
@Autowired

private BookRepository bookRepository;
@Autowired

private BookDetailRepository bookDetailRepository;
@Before

public void init() {

Book bookA = new Book("Spring in Action", new BookDetail(208));

Book bookB = new Book("Spring Data in Action", new BookDetail(235));

Book bookC = new Book("Spring Boot in Action");

bookRepository.saveAll(Arrays.asList(bookA, bookB, bookC));

}
@After

public void clear() {

bookRepository.deleteAll();

}
@Test

public void find() {

Book book = bookRepository.findByName("Spring in Action");

System.err.println(book.toString());

}
@Test

public void save() {

Book book = new Book("springboot");

BookDetail bookDetail = new BookDetail(124);

book.setBookDetail(bookDetail);

bookRepository.save(book);

}
@Test

public void delete() {
bookRepository.deleteById(31);

}

@Test

public void findbook(){

BookDetail bd = bookDetailRepository.findByNumberOfPages(235);

System.err.println(bd.toString());
}

}

　　一对多双向，相关类如下：

package io.powerx;
import lombok.Data;

import lombok.Getter;

import lombok.Setter;
import javax.persistence.*;
@Getter

@Setter

@Entity

public class Book {

@Id

@GeneratedValue

private Integer id;
private String name;
@ManyToOne

@JoinColumn(name="publishId")

private Publisher publisher;
@Override

public String toString() {

return "Book{" +

"id=" + id +

", name='" + name + ''' +

", publisher=" + publisher.getName() +

'}';

}
public Book(String name) {

this.name = name;

}
public Book() {

}

}

package io.powerx;
import lombok.Data;

import lombok.Getter;

import lombok.Setter;
import javax.persistence.*;

import java.util.HashSet;

import java.util.Set;
/**


Created by Administrator on 2018/8/16.

*/

@Getter

@Setter

@Entity

public class Publisher {

@Id

@GeneratedValue

private Integer id;
private String name;
@OneToMany(cascade = CascadeType.ALL,fetch = FetchType.EAGER)

@JoinColumn(name="publishId",referencedColumnName = "id")

private Set<Book> books;
public Publisher() {

super();

}
public Publisher(String name) {

super();

this.name = name;

}
@Override

public String toString() {

return "Publisher{" +

"id=" + id +

", name='" + name + ''' +

", books=" + books.size() +

'}';

}


}

package io.powerx;
import org.springframework.data.jpa.repository.JpaRepository;
/**


Created by Administrator on 2018/8/16.

*/

public interface BookRepository  extends JpaRepository<Book,Integer>{
Book findByName(String name);


}

package io.powerx;
import org.springframework.data.jpa.repository.JpaRepository;
/**


Created by Administrator on 2018/8/16.

*/

public interface PublisherRepository extends JpaRepository<Publisher,Integer> {
Publisher findByName(String name);

}

package io.powerx;
import org.junit.After;

import org.junit.Before;

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 java.util.HashSet;

import java.util.Set;
@RunWith(SpringRunner.class)

@SpringBootTest

public class OnetomanyApplicationTests {
@Autowired

private PublisherRepository publisherRepository;
@Autowired

private BookRepository bookRepository;
@Before

public void init() {
Book book1 = new Book("spring");

Book book2 = new Book("mvc");

Book book3 = new Book("mybatis");

Publisher publisher = new Publisher("zhonghua");

Set<Book> set = new HashSet<Book>();

set.add(book1);

set.add(book2);

set.add(book3);

publisher.setBooks(set);

publisherRepository.save(publisher);
}
@After

public void clear() {

publisherRepository.deleteAll();

}
@Test

public void find() {

Publisher publisher = publisherRepository.findByName("zhonghua");

System.out.println(publisher);

}
@Test

public void find2() {

Book book = bookRepository.findByName("mvc");

System.out.println(book);

}

}

　　多对多双向，相关代码如下：

package io.powerx;
import lombok.Getter;

import lombok.Setter;

import lombok.ToString;
import javax.persistence.*;

import java.util.Set;
@Getter

@Setter

@Entity

public class Author {
@Id

@GeneratedValue

private Integer id;
private String name;
@ManyToMany(mappedBy = "authors",fetch = FetchType.EAGER)

private Set<Book> books;
public Author() {

super();

}
public Author(String name) {

super();

this.name = name;

}
@Override

public String toString() {

return "Author{" +

"id=" + id +

", name='" + name + ''' +

", books=" + books.size() +

'}';

}

}

package io.powerx;
import lombok.Getter;

import lombok.Setter;

import lombok.ToString;
import javax.persistence.*;

import java.util.HashSet;

import java.util.Set;
@Getter

@Setter

@Entity

public class Book {
@Id

@GeneratedValue

private Integer id;
private String name;
@ManyToMany(cascade = CascadeType.ALL,fetch = FetchType.EAGER)

@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;

}
@Override

public String toString() {

return "Book{" +

"id=" + id +

", name='" + name + ''' +

", authors=" + authors.size() +

'}';

}

}

package io.powerx;
import org.springframework.data.jpa.repository.JpaRepository;
import java.util.List;
public interface AuthorRepository extends JpaRepository<Author, Integer> {
Author findByName(String name);
List<Author> findByNameContaining(String name);
}

package io.powerx;
import org.springframework.data.jpa.repository.JpaRepository;
import java.util.List;
public interface BookRepository extends JpaRepository<Book, Integer> {
Book findByName(String name);
List<Book> findByNameContaining(String name);
}

　　在调试过程中，注意实体类的tostring方法的重写，避免相互引用；此外如果超过两张表的关联查询，建议使用自定义sql，建立相应的pojo来接收查询结果。

原文地址：https://www.cnblogs.com/hhhshct/p/9492741.html

posted @ 2019-05-22 09:17 星朝阅读(3279) 评论(0) 收藏举报

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spring data jpa关联查询（一对一、一对多、多对多）

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