Spring Boot Querydsl 教程 · ZetCode 中文系列教程

# Spring Boot Querydsl 教程 > 原文： [http://zetcode.com/springboot/querydsl/](http://zetcode.com/springboot/querydsl/) Spring Boot Querydsl 教程展示了如何使用 Querydsl 在 Spring Boot 应用中创建数据库查询。 ## Querydsl Querydsl 是一个框架，可通过其流畅的 API 来构造静态类型的类似 SQL 的查询。 Spring Data 模块通过`QuerydslPredicateExecutor`与 Querydsl 集成。 ## Spring Querydsl 示例以下应用使用实体管理器和存储库使用 Querydsl 创建查询。 ```java pom.xml src ├───main │ ├───java │ │ └───com │ │ └───zetcode │ │ │ Application.java │ │ │ MyRunner.java │ │ ├───model │ │ │ City.java │ │ └───repository │ │ CityRepository.java │ └───resources │ application.properties │ data-h2.sql │ schema-h2.sql └───test └───java ``` 这是项目结构。 `pom.xml` ```java <?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>com.zetcode</groupId> <artifactId>springbootquerydsl</artifactId> <version>1.0-SNAPSHOT</version> <packaging>jar</packaging> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> <maven.compiler.source>11</maven.compiler.source> <maven.compiler.target>11</maven.compiler.target> </properties> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.1.5.RELEASE</version> </parent> <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>com.querydsl</groupId> <artifactId>querydsl-apt</artifactId> <version>4.2.1</version> <scope>provided</scope> </dependency> <dependency> <groupId>com.querydsl</groupId> <artifactId>querydsl-jpa</artifactId> <version>4.2.1</version> </dependency> </dependencies> <build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> </plugin>  <plugin> <groupId>com.mysema.maven</groupId> <artifactId>apt-maven-plugin</artifactId> <version>1.1.3</version> <executions> <execution> <phase>generate-sources</phase> <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> </project> ``` Maven POM 文件包含 Spring Data JPA，H2 数据库和 Querydsl 的依赖项。 `JPAAnnotationProcessor`查找带有`Entity`注解的域类型，并为其生成查询类型。注解处理是`javac`中的一种工具，用于在编译时扫描和处理注解。 `resources/application.properties` ```java spring.main.banner-mode=off spring.datasource.platform=h2 spring.jpa.hibernate.ddl-auto=none logging.pattern.console=%d{dd-MM-yyyy HH:mm:ss} %magenta([%thread]) %highlight(%-5level) %logger.%M - %msg%n ``` `application.properties`是主要的 Spring Boot 配置文件。使用`spring.main.banner-mode`属性，我们可以关闭 Spring 横幅。 `spring.datasource.platform`设置数据库的供应商名称。在初始化脚本中使用它。最后，`spring.jpa.hibernate.ddl-auto`禁止从实体自动创建模式。 `logging.pattern.console`定义控制台的日志模式。 `resources/schema-h2.sql` ```java CREATE TABLE cities(id INT PRIMARY KEY AUTO_INCREMENT, name VARCHAR(255), population INT); ``` 启动应用时，将执行`schema-h2.sql`脚本。它创建一个新的数据库表。 `resources/data-h2.sql` ```java INSERT INTO cities(name, population) VALUES('Bratislava', 432000); INSERT INTO cities(name, population) VALUES('Budapest', 1759000); INSERT INTO cities(name, population) VALUES('Prague', 1280000); INSERT INTO cities(name, population) VALUES('Warsaw', 1748000); INSERT INTO cities(name, population) VALUES('Los Angeles', 3971000); INSERT INTO cities(name, population) VALUES('New York', 8550000); INSERT INTO cities(name, population) VALUES('Edinburgh', 464000); INSERT INTO cities(name, population) VALUES('Suzhou', 4327066); INSERT INTO cities(name, population) VALUES('Zhengzhou', 4122087); INSERT INTO cities(name, population) VALUES('Berlin', 3671000); INSERT INTO cities(name, population) VALUES('Brest', 139163); INSERT INTO cities(name, population) VALUES('Bucharest', 1836000); ``` 之后，执行`data-h2.sql`文件。它用数据填充表。 `com/zetcode/model/City.java` ```java package com.zetcode.model; import java.util.Objects; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; import javax.persistence.Table; @Entity @Table(name = "cities") public class City { @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; private String name; private int population; public City() { } public City(String name, int population) { this.name = name; this.population = population; } 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 int getPopulation() { return population; } public void setPopulation(int population) { this.population = population; } @Override public int hashCode() { int hash = 7; hash = 79 * hash + Objects.hashCode(this.id); hash = 79 * hash + Objects.hashCode(this.name); hash = 79 * hash + this.population; return hash; } @Override public boolean equals(Object obj) { if (this == obj) { return true; } if (obj == null) { return false; } if (getClass() != obj.getClass()) { return false; } final City other = (City) obj; if (this.population != other.population) { return false; } if (!Objects.equals(this.name, other.name)) { return false; } return Objects.equals(this.id, other.id); } @Override public String toString() { var builder = new StringBuilder(); builder.append("City{id=").append(id).append(", name=") .append(name).append(", population=") .append(population).append("}"); return builder.toString(); } } ``` 这是`City`实体。 `com/zetcode/repository/CityRepository.java` ```java package com.zetcode.repository; import com.zetcode.model.City; import org.springframework.data.querydsl.QuerydslPredicateExecutor; import org.springframework.data.repository.CrudRepository; import org.springframework.stereotype.Repository; @Repository public interface CityRepository extends CrudRepository<City, Long>, QuerydslPredicateExecutor<City> { } ``` 要在我们的存储库中启用 Querydsl，我们从`QuerydslPredicateExecutor`扩展。 `com/zetcode/MyRunner.java` ```java package com.zetcode; import com.querydsl.core.types.OrderSpecifier; import com.querydsl.core.types.dsl.BooleanExpression; import com.querydsl.jpa.impl.JPAQuery; import com.zetcode.model.QCity; import com.zetcode.repository.CityRepository; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.boot.CommandLineRunner; import org.springframework.stereotype.Component; import javax.persistence.EntityManager; import javax.persistence.PersistenceContext; @Component @SuppressWarnings({ "rawtypes", "unchecked" }) public class MyRunner implements CommandLineRunner { private static final Logger logger = LoggerFactory.getLogger(MyRunner.class); @PersistenceContext private EntityManager entityManager; @Autowired private CityRepository cityRepository; @Override public void run(String... args) throws Exception { var qCity = QCity.city; var query = new JPAQuery(entityManager); query.from(qCity).where(qCity.name.eq("Bratislava")).distinct(); var c1 = query.fetch(); logger.info("{}", c1); var query2 = new JPAQuery(entityManager); query2.from(qCity).where(qCity.name.endsWith("est").and(qCity.population.lt(1800000))); var cities = query2.fetch(); logger.info("{}", cities); BooleanExpression booleanExpression = qCity.population.goe(2_000_000); OrderSpecifier<String> orderSpecifier = qCity.name.asc(); var cities2 = cityRepository.findAll(booleanExpression, orderSpecifier); logger.info("{}", cities2); } } ``` 我们使用`EntityManager`和`CityRepository`创建 Querydsl 查询。 ```java var qCity = QCity.city; ``` Querydsl 创建一个`QCity`类型。 ```java var query = new JPAQuery(entityManager); ``` 在前两个查询中，我们使用实体管理器。 ```java query.from(qCity).where(qCity.name.eq("Bratislava")).distinct(); var c1 = query.fetch(); logger.info("{}", c1); ``` 使用 Querydsl 的流畅 API，我们获取了一个独特的城市对象。 ```java var query2 = new JPAQuery(entityManager); query2.from(qCity).where(qCity.name.endsWith("est").and(qCity.population.lt(1800000))); var cities = query2.fetch(); logger.info("{}", cities); ``` 一个更复杂的查询将获取多个城市。 ```java BooleanExpression booleanExpression = qCity.population.goe(2_000_000); OrderSpecifier<String> orderSpecifier = qCity.name.asc(); var cities2 = cityRepository.findAll(booleanExpression, orderSpecifier); logger.info("{}", cities2); ``` 在第三个查询中，我们利用存储库。 > **注意**：在Java企业应用中，定义与存储库一起使用的服务层是一个好习惯。为简单起见，我们跳过服务层。 `com/zetcode/Application.java` ```java package com.zetcode; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; @SpringBootApplication public class Application { public static void main(String[] args) { SpringApplication.run(Application.class, args); } } ``` `Application`设置 Spring Boot 应用。 `@SpringBootApplication`启用自动配置和组件扫描。 ```java $ mvn spring-boot:run ... 04-06-2019 13:22:13 [main] INFO com.zetcode.MyRunner.run - [City{id=1, name=Bratislava, population=432000}] 04-06-2019 13:22:13 [main] INFO com.zetcode.MyRunner.run - [City{id=2, name=Budapest, population=1759000}, City{id=11, name=Brest, population=139163}] 04-06-2019 13:22:13 [main] INFO com.zetcode.MyRunner.run - [City{id=10, name=Berlin, population=3671000}, City{id=5, name=Los Angeles, population=3971000}, City{id=6, name=New York, population=8550000}, City{id=8, name=Suzhou, population=4327066}, City{id=9, name=Zhengzhou, population=4122087}] ... ``` 我们运行该应用。在本教程中，我们展示了如何使用 Querydsl 在 Spring Boot 应用中生成查询。 * [Spring Boot `TestEntityManager`教程](/springboot/testentitymanager/) * [Spring Boot Data JPA `@NamedQuery`教程](/springboot/datajpanamedquery/) * [Spring Boot REST Data JPA 教程](/articles/springbootrestdatajpa/) [](/articles/springbootrestdatajpa/) * [Spring Boot Data JPA 排序教程](/springboot/datajpasort/) * [Spring Boot `CrudRepository`教程](/springboot/crudrepository/) 列出[所有 Spring Boot 教程](/all/#springboot)。