Spring Boot Data JPA 派生的查询 · ZetCode 中文系列教程

# Spring Boot Data JPA 派生的查询 > 原文： [http://zetcode.com/springboot/datajpaderivedqueries/](http://zetcode.com/springboot/datajpaderivedqueries/) Spring Boot Data JPA 派生查询教程展示了如何从方法名称创建查询。 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 派生的查询 Spring Data JPA 可以从方法名称创建查询。这是约定而不是配置的特定形式。 Spring Data JPA 从具有属性组合的特定关键字创建查询；例如：`findByAgeLessThan`，`findByFirstnameEndingWith`或`findByFirstnameEquals`。关键字列表在 Spring Data JPA [文档](https://docs.spring.io/spring-data/jpa/docs/current/reference/html/#jpa.query-methods.query-creation)中提供。 ## Spring Boot Data JPA 派生查询示例以下应用使用两个派生查询。 ```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>springbootderivedqueries</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`。 ```java @Entity @Table(name = "cities") public class City { ``` `@Entity`注解指定该类是一个实体，并映射到数据库表。 `@Table`注解指定要用于映射的数据库表的名称。 ```java @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; ``` `@Id`注解指定实体的主键，`@GeneratedValue`提供规范主键值的生成策略。 `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.stereotype.Repository; import java.util.List; @Repository public interface CityRepository extends CrudRepository<City, Long> { List<City> findByNameEndingWith(String ending); List<City> findByPopulationLessThan(int population); } ``` 我们有两种方法可以从中生成派生查询。 ```java List<City> findByNameEndingWith(String ending); ``` 在这里，查询将查找以指定字符串结尾的表单城市名称。 ```java List<City> findByPopulationLessThan(int population); ``` 查询将在其中查找人口少于指定数量的城市。 `com/zetcode/service/ICityService.java` ```java package com.zetcode.service; import com.zetcode.model.City; import java.util.List; public interface ICityService { List<City> findByNameEndingWith(String ending); List<City> findByPopulationLessThan(int population); } ``` `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.stereotype.Service; import java.util.List; @Service public class CityService implements ICityService { @Autowired private CityRepository cityRepository; @Override public List<City> findByNameEndingWith(String ending) { return cityRepository.findByNameEndingWith(ending); } @Override public List<City> findByPopulationLessThan(int population) { return cityRepository.findByPopulationLessThan(population); } } ``` `CityService`包含服务方法实现。派生的查询在`cityRepository`上调用。 `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 having population less than one million"); var res1 = cityService.findByPopulationLessThan(1000000); logger.info("{}", res1); logger.info("Finding cities by name ending with 'est'"); var res2 = cityService.findByNameEndingWith("est"); logger.info("{}", res2); } } ``` `MyRunner`获取所有人口少于一百万的城市以及所有名称以`"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 ... 19-05-21 Tue 14:53:39.892 INFO MyRunner [City{id=1, name=Bratislava, population=432000}, City{id=7, name=Brest, population=139163}, City{id=8, name=Edinburgh, population=464000}] 19-05-21 Tue 14:53:39.894 INFO MyRunner Finding cities by name ending with 'est' 19-05-21 Tue 14:53:39.903 INFO 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 派生的查询来获取数据。您可能也对相关教程感兴趣： * [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)。