Spring Boot Data JPA 查询示例 · ZetCode 中文系列教程

# Spring Boot Data JPA 示例查询 > 原文： [http://zetcode.com/springboot/datajpaquerybyexample/](http://zetcode.com/springboot/datajpaquerybyexample/) Spring Boot Data JPA 示例查询教程展示了如何使用 Spring Data JPA 示例查询技术创建查询。 Spring 是用于创建企业应用的流行 Java 应用框架。 Spring Boot 是 Spring 框架的演进，可帮助您轻松创建独立的，生产级的基于 Spring 的应用。 ## Spring Data JPA Spring Data JPA 有助于实现基于 JPA 的存储库。它增强了对基于 JPA 的数据访问层的支持。它使构建使用数据访问技术的 Spring 支持的应用变得更加容易。 Spring Data JPA 是较大的 Spring Data 系列的一部分。 ## Spring Data JPA 查询示例示例查询（QBE）是一种具有简单接口的用户友好查询技术。它允许动态查询创建。我们不需要使用商店特定的查询语言编写查询。我们处理三个对象。 `probe`是带有填充字段的域对象的实际示例。 `ExampleMatcher`包含有关如何匹配特定字段的详细信息。 `Example`由探针和`ExampleMatcher`组成。它用于创建查询。 QBE 有一些局限性。它无法创建一些更高级的查询。 ## Spring Boot Data JPA QBE 示例以下应用使用 QBE 生成查询。 ```java pom.xml src ├───main │ ├───java │ │ └───com │ │ └───zetcode │ │ │ Application.java │ │ │ MyRunner.java │ │ ├───model │ │ │ City.java │ │ ├───repository │ │ │ CityRepository.java │ │ └───service │ │ CityService.java │ │ ICityService.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>springbootquerybyexample</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>2.1.1.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> </dependencies> <build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> </plugin> </plugins> </build> </project> ``` Maven POM 文件包含 H2 数据库和 Spring Boot Data JPA 的依赖项。 `resources/application.properties` ```java spring.main.banner-mode=off spring.datasource.platform=h2 spring.jpa.hibernate.ddl-auto=none ``` 在`application.properties`文件中，我们编写了 Spring Boot 应用的各种配置设置。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。 `spring.jpa.hibernate.ddl-auto`禁止从实体自动创建模式。 `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。每个实体必须至少定义两个注解：`@Entity`和`@Id`。 `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('Brest', 139163); 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('Bucharest', 1836000); ``` 之后，执行`data-h2.sql`文件。它用数据填充表。 `com/zetcode/repository/CityRepository.java` ```java package com.zetcode.repository; import com.zetcode.model.City; import org.springframework.data.repository.CrudRepository; import org.springframework.data.repository.query.QueryByExampleExecutor; import org.springframework.stereotype.Repository; @Repository public interface CityRepository extends CrudRepository<City, Long>, QueryByExampleExecutor<City> { } ``` 我们通过从`QueryByExampleExecutor`扩展存储库来启用 QBE API。 `com/zetcode/service/ICityService.java` ```java package com.zetcode.service; import com.zetcode.model.City; import java.util.List; public interface ICityService { List<City> findByNameEnding(String ending); List<City> findByName(String name); } ``` `ICityService`提供了两种签约方法。 `com/zetcode/service/CityService.java` ```java package com.zetcode.service; import com.zetcode.model.City; import com.zetcode.repository.CityRepository; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.data.domain.Example; import org.springframework.data.domain.ExampleMatcher; import org.springframework.stereotype.Service; import java.util.List; import static org.springframework.data.domain.ExampleMatcher.GenericPropertyMatchers.exact; @Service public class CityService implements ICityService { @Autowired private CityRepository cityRepository; @Override public List<City> findByNameEnding(String ending) { var city = new City(); city.setName(ending); var matcher = ExampleMatcher.matching() .withMatcher("name", match -> match.endsWith()) .withIgnorePaths("population"); var example = Example.of(city, matcher); return (List<City>) cityRepository.findAll(example); } @Override public List<City> findByName(String name) { var city = new City(); city.setName(name); var matcher = ExampleMatcher.matching() .withMatcher("name", exact()) .withIgnorePaths("population"); var example = Example.of(city, matcher); return (List<City>) cityRepository.findAll(example); } } ``` `CityService`包含服务方法实现。 ```java var city = new City(); city.setName(ending); ``` 我们有一个`City`域对象。这称为探针。 ```java var matcher = ExampleMatcher.matching() .withMatcher("name", match -> match.endsWith()) .withIgnorePaths("population"); ``` 匹配器将以城市名称结尾的字符串匹配，并忽略人口。 ```java var example = Example.of(city, matcher); ``` 根据域对象和匹配器创建一个`Example`。 ```java return (List<City>) cityRepository.findAll(example); ``` `Example`传递给`findAll()`方法。 `com/zetcode/MyRunner.java` ```java package com.zetcode; import com.zetcode.service.ICityService; 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; @Component public class MyRunner implements CommandLineRunner { private static final Logger logger = LoggerFactory.getLogger(MyRunner.class); @Autowired private ICityService cityService; @Override public void run(String... args) throws Exception { logger.info("Finding cities by name"); var res1 = cityService.findByName("Bratislava"); logger.info("{}", res1); var res2 = cityService.findByName("Berlin"); logger.info("{}", res2); logger.info("Finding cities by name ending with est"); var res3 = cityService.findByNameEnding("est"); logger.info("{}", res3); } } ``` `MyRunner`查找`"Bratislava"`和`"Berlin"`城市，并找到所有名称以`"est"`结尾的城市。 `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 ... 2019-05-21 16:24:33.480 com.zetcode.MyRunner Finding cities by name 2019-05-21 16:24:33.771 com.zetcode.MyRunner [City{id=1, name=Bratislava, population=432000}] 2019-05-21 16:24:33.773 com.zetcode.MyRunner [City{id=11, name=Berlin, population=3671000}] 2019-05-21 16:24:33.774 com.zetcode.MyRunner Finding cities by name ending with est 2019-05-21 16:24:33.781 com.zetcode.MyRunner [City{id=2, name=Budapest, population=1759000}, City{id=7, name=Brest, population=139163}, City{id=12, name=Bucharest, population=1836000}] ... ``` 我们运行该应用。在本教程中，我们使用了 Spring Data JPA 示例查询技术来生成查询。您可能也对相关教程感兴趣： * [Spring Boot Data JPA `@NamedQuery`教程](/springboot/datajpanamedquery/) * [Spring Boot Data JPA 派生查询教程](/springboot/datajpaderivedqueries/) * [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)。