你知道Spring Data JPA如何实现多表关联查询吗?通常来说有2种实现方式，下面一起来了解一下吧。
1、利用hibernate级联查询来实现
2、创建一个结果集的接口来接收连表查询后的结果
下面的话来介绍一下第2种方式。
1、一对一映射
实体UserInfo：用户。
实体Address：家庭住址。
通过外键的方式来实现一对一关联(一个实体通过外键关联到另一个实体的主键)
实体类
(1)实体类 UserInfo.java
package com.johnfnash.learn.domain;
import java.io.Serializable;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;
@Entity
@Table(name = "tb_user")
public class UserInfo implements Serializable
{
private static final long serialVersionUID = 8283950216116626180 L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long userId;
private String name;
private int age;
private String sex;
private String email;
// 与 Address 的关联
private Long addressId;
public UserInfo()
{
super();
}
public UserInfo(String name, int age, String sex, String email, Long addressId)
{
super();
this.name = name;
this.age = age;
this.sex = sex;
this.email = email;
this.addressId = addressId;
}
// getter, setter
@Override
public String toString()
{
return String.format("UserInfo [userId=%d, name=%s, age=%s, sex=%s, email=%s]", userId, name, age, sex, email);
}
}(2)实体类 Address.java
package com.johnfnash.learn.domain;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;
@Entity
@Table(name = "tb_address")
public class Address
{
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long addressId;
private String areaCode;
private String country;
private String province;
private String city;
private String area;
private String detailAddress;
public Address()
{
super();
}
public Address(String areaCode, String country, String province, String city, String area
, String detailAddress)
{
super();
this.areaCode = areaCode;
this.country = country;
this.province = province;
this.city = city;
this.area = area;
this.detailAddress = detailAddress;
}
// getter, setter
@Override
public String toString()
{
return "Address [addressId=" + addressId + ", areaCode=" + areaCode + ", country=" + country + ", province=" +
province + ", city=" + city + ", area=" + area + ", detailAddress=" + detailAddress + "]";
}
}Dao层
(1)UserInfoRepository.java
package com.johnfnash.learn.repository;
import java.util.List;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import com.johnfnash.learn.domain.UserInfo;
import com.johnfnash.learn.domain.ViewInfo;
public interface UserInfoRepository extends JpaRepository < UserInfo, Long >
{
@Query(value = "SELECT new com.johnfnash.learn.domain.ViewInfo(u, a) FROM UserInfo u, Address a WHERE u.addressId = a.addressId")
public List < ViewInfo > findViewInfo();
}注：这里的ViewInfo 类用来一个用来接收多表查询结果集的类(使用 new + 完整类名构造函数)
代码：
package com.johnfnash.learn.domain;
import java.io.Serializable;
public class ViewInfo implements Serializable
{
private static final long serialVersionUID = -6347911007178390219 L;
private UserInfo userInfo;
private Address address;
public ViewInfo()
{}
public ViewInfo(UserInfo userInfo)
{
Address address = new Address();
this.userInfo = userInfo;
this.address = address;
}
public ViewInfo(Address address)
{
UserInfo userInfo = new UserInfo();
this.userInfo = userInfo;
this.address = address;
}
public ViewInfo(UserInfo userInfo, Address address)
{
this.userInfo = userInfo;
this.address = address;
}
// getter, setter
}(2)AddressRepository.java
package com.johnfnash.learn.repository;
import org.springframework.data.jpa.repository.JpaRepository;
import com.johnfnash.learn.domain.Address;
public interface AddressRepository extends JpaRepository < Address, Long >
{}测试代码
package com.johnfnash.learn;
import java.util.List;
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 com.johnfnash.learn.domain.Address;
import com.johnfnash.learn.domain.UserInfo;
import com.johnfnash.learn.domain.ViewInfo;
import com.johnfnash.learn.repository.AddressRepository;
import com.johnfnash.learn.repository.UserInfoRepository;
@RunWith(SpringRunner.class)
@SpringBootTest
public class UserInfoRepositoryTests
{
@Autowired
private UserInfoRepository userInfoRepository;
@Autowired
private AddressRepository addressRepository;
@Before
public void init()
{
Address addr1 = new Address("027", "CN", "HuBei", "WuHan", "WuChang", "123 street");
Address addr2 = new Address("023", "CN", "ChongQing", "ChongQing", "YuBei", "123 road");
addressRepository.save(addr1);
addressRepository.save(addr2);
UserInfo user1 = new UserInfo("ZS", 21, "Male", "123@xx.com", addr1.getAddressId());
UserInfo user2 = new UserInfo("Ww", 25, "Male", "234@xx.com", addr2.getAddressId());
userInfoRepository.save(user1);
userInfoRepository.save(user2);
}
@After
public void deleteAll()
{
userInfoRepository.deleteAll();
addressRepository.deleteAll();
}
@Test
public void testQuery()
{
List < ViewInfo > viewInfos = userInfoRepository.findViewInfo();
for (ViewInfo viewInfo: viewInfos)
{
System.out.println(viewInfo.getUserInfo());
System.out.println(viewInfo.getAddress());
}
}
}查询相关的sql ：
Hibernate: select userinfo0_.user_id as col_0_0_, address1_.address_id as col_1_0_ from tb_user userinfo0_ cross join tb_address address1_ where userinfo0_.address_id = address1_.address_id Hibernate: select userinfo0_.user_id as user_id1_4_0_, userinfo0_.address_id as address_2_4_0_, userinfo0_.age as age3_4_0_, userinfo0_.email as email4_4_0_, userinfo0_.name as name5_4_0_, userinfo0_.sex as sex6_4_0_ from tb_user userinfo0_ where userinfo0_.user_id = ? Hibernate : select address0_.address_id as address_1_3_0_, address0_.area as area2_3_0_, address0_.area_code as area_cod3_3_0_, address0_.city as city4_3_0_, address0_.country as country5_3_0_, address0_.detail_address as detail_a6_3_0_, address0_.province as province7_3_0_ from tb_address address0_ where address0_.address_id = ? Hibernate : select userinfo0_.user_id as user_id1_4_0_, userinfo0_.address_id as address_2_4_0_, userinfo0_.age as age3_4_0_, userinfo0_.email as email4_4_0_, userinfo0_.name as name5_4_0_, userinfo0_.sex as sex6_4_0_ from tb_user userinfo0_ where userinfo0_.user_id = ? Hibernate : select address0_.address_id as address_1_3_0_, address0_.area as area2_3_0_, address0_.area_code as area_cod3_3_0_, address0_.city as city4_3_0_, address0_.country as country5_3_0_, address0_.detail_address as detail_a6_3_0_, address0_.province as province7_3_0_ from tb_address address0_ where address0_.address_id = ? Hibernate : select userinfo0_.user_id as user_id1_4_, userinfo0_.address_id as address_2_4_, userinfo0_.age as age3_4_, userinfo0_.email as email4_4_, userinfo0_.name as name5_4_, userinfo0_.sex as sex6_4_ from tb_user userinfo0_ Hibernate: select address0_.address_id as address_1_3_, address0_.area as area2_3_, address0_.area_code as area_cod3_3_, address0_.city as city4_3_, address0_.country as country5_3_, address0_.detail_address as detail_a6_3_, address0_.province as province7_3_ from tb_address address0_
查询结果：
UserInfo[userId = 1, name = ZS, age = 21, sex = Male, email = 123 @xx.com] Address[addressId = 1, areaCode = 027, country = CN, province = HuBei, city = WuHan, area = WuChang, detailAddress = 123 street] UserInfo[userId = 2, name = Ww, age = 25, sex = Male, email = 234 @xx.com] Address[addressId = 2, areaCode = 023, country = CN, province = ChongQing, city = ChongQing, area = YuBei, detailAddress = 123 road]
2、多对多映射
实体Author ：作者。
实体Book ：书籍
这里通过关联表的方式来实现多对多关联。
实体类
实体类：Author.java
package com.johnfnash.learn.domain;
import java.io.Serializable;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
@Entity
public class Author implements Serializable
{
private static final long serialVersionUID = 1227555837798655046 L;
@Id
@GeneratedValue
private Integer id;
private String name;
public Author()
{
super();
}
public Author(String name)
{
super();
this.name = name;
}
// getter, setter
@Override
public String toString()
{
return String.format("Author [id=%s, name=%s]", id, name);
}
}Book.java 实体类
package com.johnfnash.learn.domain;
import java.io.Serializable;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
@Entity
public class Book implements Serializable
{
private static final long serialVersionUID = -2470510857424220408 L;
@Id
@GeneratedValue
private Integer id;
private String name;
public Book()
{
super();
}
public Book(String name)
{
super();
this.name = name;
}
//getter, setter
@Override
public String toString()
{
return String.format("Book [id=%s, name=%s]", id, name);
}
}实体类BookAuthor.java
package com.johnfnash.learn.domain;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.IdClass;
import javax.persistence.Table;
@Entity
@IdClass(BookAuthorPK.class)
@Table(name = "book_author")
public class BookAuthor
{
@Id
private Integer bookId;
@Id
private Integer authorId;
public BookAuthor()
{
super();
}
public BookAuthor(Integer bookId, Integer authorId)
{
super();
this.bookId = bookId;
this.authorId = authorId;
}
// getter, setter
}注：这里使用@IdClass注解指定一个联合主键类来映射实体类的多个属性。
联合主键类的代码：
package com.johnfnash.learn.domain;
import java.io.Serializable;
public class BookAuthorPK implements Serializable
{
private static final long serialVersionUID = -1158141803682305656 L;
private Integer bookId;
private Integer authorId;
public Integer getBookId()
{
return bookId;
}
public void setBookId(Integer bookId)
{
this.bookId = bookId;
}
public Integer getAuthorId()
{
return authorId;
}
public void setAuthorId(Integer authorId)
{
this.authorId = authorId;
}
}Dao 层
BookRepository.java
package com.johnfnash.learn.repository;
import java.util.List;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import com.johnfnash.learn.domain.Book;
public interface BookRepository extends JpaRepository < Book, Integer >
{
@Query(nativeQuery = true, value = "SELECT b.id, b.name, GROUP_CONCAT(a.name) as authorName from book b, author a, book_author ba" +
" where b.id = ba.book_id and a.id = ba.author_id and b.name like ?1 group by b.id, b.name")
List < Object[] > findByNameContaining(String name);
}注：这里使用nativeQuery=true指定使用原生SQL进行查询;这里使用了 mysql 的内置函数 GROUP_CONCAT 进行行转列, HQL 无法直接识别;
注：可能会出现 Caused by: org.hibernate.QueryException: No data type for node: org.hibernate.hql.internal.ast.tree.MethodNode 的错误
JpaRepository.java
package com.johnfnash.learn.repository;
import org.springframework.data.jpa.repository.JpaRepository;
import com.johnfnash.learn.domain.Author;
public interface AuthorRepository extends JpaRepository < Author, Integer >
{}BookAuthorRepository.java
package com.johnfnash.learn.repository;
import org.springframework.data.jpa.repository.JpaRepository;
import com.johnfnash.learn.domain.BookAuthor;
public interface BookAuthorRepository extends JpaRepository < BookAuthor, Integer >
{}测试代码
package com.johnfnash.learn;
import static org.junit.Assert.assertEquals;
import java.util.List;
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 com.johnfnash.learn.domain.Author;
import com.johnfnash.learn.domain.Book;
import com.johnfnash.learn.domain.BookAuthor;
import com.johnfnash.learn.repository.AuthorRepository;
import com.johnfnash.learn.repository.BookAuthorRepository;
import com.johnfnash.learn.repository.BookRepository;
@RunWith(SpringRunner.class)
@SpringBootTest
public class BookRepositoryTests
{
@Autowired
private BookRepository bookRepository;
@Autowired
private AuthorRepository authorRepository;
@Autowired
private BookAuthorRepository bookAuthorRepository;
@Before
public void init()
{
Author lewis = new Author("Lewis");
Author mark = new Author("Mark");
Author peter = new Author("Peter");
authorRepository.save(lewis);
authorRepository.save(mark);
authorRepository.save(peter);
Book spring = new Book("Spring in Action");
Book springboot = new Book("Spring Boot in Action");
bookRepository.save(spring);
bookRepository.save(springboot);
bookAuthorRepository.save(new BookAuthor(spring.getId(), lewis.getId()));
bookAuthorRepository.save(new BookAuthor(spring.getId(), mark.getId()));
bookAuthorRepository.save(new BookAuthor(springboot.getId(), mark.getId()));
bookAuthorRepository.save(new BookAuthor(springboot.getId(), peter.getId()));
}
@After
public void deleteAll()
{
bookAuthorRepository.deleteAll();
bookRepository.deleteAll();
authorRepository.deleteAll();
}
@Test
public void findAll()
{
assertEquals(bookRepository.findAll()
.size(), 2);
assertEquals(authorRepository.findAll()
.size(), 3);
List < Object[] > books = bookRepository.findByNameContaining("Spring%");
for (Object[] book: books)
{
for (Object object: book)
{
System.out.print(object + ", ");
}
System.out.println();
}
}
}执行findAll方法之后，查询的相关SQL如下：
Hibernate: SELECT b.id, b.name, GROUP_CONCAT(a.name) as authorName from book b, author a, book_author ba where b.id = ba.book_id and a.id = ba.author_id and b.name like ? group by b.id, b.name
输出的结果如下：
3652, Spring in Action, Lewis, Mark , 3653, Spring Boot in Action, Mark, Peter,
以上内容源于网络仅供参考。
jpa实现多表关联查询的内容你都了解了吗?更多java程序代码例子，可以继续关注本站来进行了解哦。
推荐阅读：