多表查詢在spring data jpa中有兩種實現方式，第一種是利用hibernate的級聯查詢來實現，第二種是建立一個結果集的介面來接收連表查詢後的結果，這裡介紹第二種方式。

一、一對一對映

實體 UserInfo ：使用者。

實體 Address：家庭住址。

這裡通過外來鍵的方式(一個實體通過外來鍵關聯到另一個實體的主鍵)來實現一對一關聯。

實體類

1、實體類 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 = 8283950216116626180L;

  @Id
  @GeneratedValue(strategy=GenerationType.IDENTITY)
  private Long userId;
  private String name;
  private int age;
  private String sex;
  private String email;

  // 與 Address 的關聯  
  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. 實體類 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 層

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：這裡的 ViewInfo 類用來一個用來接收多表查詢結果集的類（使用 new + 完整類名建構函式） 
程式碼如下：

package com.johnfnash.learn.domain;

import java.io.Serializable;

public class ViewInfo implements Serializable {

  private static final long serialVersionUID = -6347911007178390219L;

  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> {

}

測試程式碼

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","[email protected]", addr1.getAddressId());
        UserInfo user2 = new UserInfo("Ww", 25,"Male","[email protected]", 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());
    }
  }

}

查詢相關的 sql 如下：

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_

查詢結果如下：

UserInfo [userId=1, name=ZS, age=21, sex=Male, [email protected]]
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 protected]]
Address [addressId=2, areaCode=023, country=CN, province=ChongQing, city=ChongQing, area=YuBei, detailAddress=123 road]

二、多對多對映

實體 Author ：作者。

實體 Book ：書籍

這裡通過關聯表的方式來實現多對多關聯。

實體類

實體類：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 = 1227555837798655046L;

  @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 實體類

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 = -2470510857424220408L;

  @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);
  }

}

實體類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：這裡使用 @IdClass 註解指定一個聯合主鍵類來對映實體類的多個屬性。這個聯合主鍵類的程式碼如下：

package com.johnfnash.learn.domain;

import java.io.Serializable;

public class BookAuthorPK implements Serializable {

  private static final long serialVersionUID = -1158141803682305656L;

  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 層

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： 
1）這裡使用 nativeQuery = true 指定使用原生 SQL 進行查詢（個人覺得複雜的查詢使用原生SQL更好 
2）這裡使用了 mysql 的內建函式 GROUP_CONCAT 進行行轉列, HQL 無法直接識別。可能會出現 Caused by: org.hibernate.QueryException: No data type for node: org.hibernate.hql.internal.ast.tree.MethodNode 的錯誤

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> {

}

測試程式碼

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();
    }
  }

}

執行 findAll 方法後，查詢的相關 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

輸出的結果如下：

3652, Spring in Action, Lewis,Mark, 
3653, Spring Boot in Action, Mark,Peter, 

參考

(1) Spring Data JPA 實現多表關聯查詢

(2) springboot(五): spring data jpa的使用

文章轉載自：https://blog.csdn.net/johnf_nash/article/details/80587204