极客教程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。
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
<?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 for query-dsl-->
<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
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 标语。 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
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
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
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
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
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。
var qCity = QCity.city;
Querydsl 创建一个QCity类型。
var query = new JPAQuery(entityManager);
在前两个查询中，我们使用实体管理器。
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。
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。
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。
Note: In Java enterprise applications it is a good practice to define a service layer that works with repositories. For simplicity reasons, we skip the service layer.
com/zetcode/Application.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。
$ 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。