之前研究Jooq，今天來研究一下搭配JPA的QueryDSL吧。

簡介

Querydsl 是一個Java開源框架用於構建型別安全的SQL查詢語句。它採用API代替拼湊字串來構造查詢語句。可跟 Hibernate 和 JPA 等框架結合使用。

新建Spring Boot專案

。。。還說啥？

1. pom.xml

<dependencies>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-data-jpa</artifactId>
    </dependency>
    
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
 
    <dependency>
      <groupId>mysql</groupId>
      <artifactId>mysql-connector-java</artifactId>
      <scope>runtime</scope>
    </dependency>
 
    <!--QueryDSL支援-->
    <dependency>
      <groupId>com.querydsl</groupId>
      <artifactId>querydsl-apt</artifactId>
      <scope>provided</scope>
    </dependency>
    
    <!--QueryDSL支援-->
    <dependency>
      <groupId>com.querydsl</groupId>
      <artifactId>querydsl-jpa</artifactId>
    </dependency>
 
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-test</artifactId>
      <scope>test</scope>
      <exclusions>
        <exclusion>
          <groupId>org.junit.vintage</groupId>
          <artifactId>junit-vintage-engine</artifactId>
        </exclusion>
      </exclusions>
    </dependency>
  </dependencies>
 
  <build>
    <plugins>
      <plugin>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-maven-plugin</artifactId>
      </plugin>
	  <!-- 這個外掛是為了讓程式自動生成query type(查詢實體，命名方式為："Q"+對應實體名) -->
      <plugin>
        <groupId>com.mysema.maven</groupId>
        <artifactId>apt-maven-plugin</artifactId>
        <version>1.1.3</version>
        <executions>
          <execution>
            <goals>
              <goal>process</goal>
            </goals>
            <configuration>
              <outputDirectory>target/generated-sources/java</outputDirectory>
              <processor>com.querydsl.apt.jpa.JPAAnnotationProcessor</processor>
            </configuration>
          </execution>
        </executions>
      </plugin>
    </plugins>
  </build>

2. application.yml

server:
 port: 8888
spring:
 datasource:
  url: jdbc:mysql://IP地址:3306/querydsl?characterEncoding=UTF-8
  username: 使用者名稱
  password: 密碼
 jpa:
  show-sql: true # 控制檯列印SQL
  hibernate:
   ddl-auto: update

3. JPAQueryFactory Bean

/**
 * JPAQueryFactory Bean
 * @author zhouzhaodong
 */
@Configuration
public class PeopleQueryConfig {
  @Bean
  public JPAQueryFactory jpaQuery(EntityManager entityManager) {
    return new JPAQueryFactory(entityManager);
  }
}

4. 新建實體類

/**
 * 實體類
 * @author zhouzhaodong
 */
@Entity
@Table(name="people")
public class People {
 
  @Id
  @Column(name="id")
  @GeneratedValue
  private Integer id;
 
  @Column(name="name")
  private String name;
 
  @Column(name="age")
  private Integer age;
 
  @Column(name="address")
  private String address;
 
  public Integer getId() {
    return id;
  }
 
  public void setId(Integer id) {
    this.id = id;
  }
 
  public String getName() {
    return name;
  }
 
  public void setName(String name) {
    this.name = name;
  }
 
  public Integer getAge() {
    return age;
  }
 
  public void setAge(Integer age) {
    this.age = age;
  }
 
  public String getAddress() {
    return address;
  }
 
  public void setAddress(String address) {
    this.address = address;
  }
}

5. 新建service

/**
 * service
 * @author zhouzhaodong
 */
public interface PeopleService {
 
  /**
   * 根據id查詢
   * @param id
   * @return
   */
  People selectOne(Integer id);
 
}

6. 新建serviceImpl

/**
 * serviceImpl
 * @author zhouzhaodong
 */
@Service
public class PeopleServiceImpl implements PeopleService {
 
  @Resource
  JPAQueryFactory queryFactory;
 
  @Override
  public People selectOne(Integer id) {
    QPeople people = QPeople.people;
    return queryFactory.selectFrom(people).where(people.id.eq(id)).fetchOne();
  }
}

7. 新建controller

/**
 * controller
 * @author zhouzhaodong
 */
@RestController
public class PeopleController {
 
  @Resource
  PeopleService peopleService;
 
  @RequestMapping("/selectById")
  public People selectById(){
    return peopleService.selectOne(0);
  }
 
}

8. 新建repository，可以使用JPA原有的功能

/**
 * 實現jpaRepository
 * @author zhouzhaodong
 */
public interface PeopleRepository extends JpaRepository<People,Integer> {
}

9. postman測試

資料庫資料如下：

請求結果：

Github程式碼地址：https://github.com/zhouzhaodong/springboot/tree/master/querydsl

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