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

# Spring Boot Data JPA 派生的查詢 > 原文： [http://zetcode.com/springboot/datajpaderivedqueries/](http://zetcode.com/springboot/datajpaderivedqueries/) Spring Boot Data JPA 派生查詢教程展示了如何從方法名稱創建查詢。 Spring 是用于創建企業應用的流行 Java 應用框架。 Spring Boot 是 Spring 框架的演進，可幫助您輕松創建獨立的，生產級的基于 Spring 的應用。 ## Spring Data JPA Spring Data JPA 有助于實現基于 JPA 的存儲庫。它增強了對基于 JPA 的數據訪問層的支持。它使構建使用數據訪問技術的 Spring 支持的應用變得更加容易。 Spring Data JPA 是較大的 Spring Data 系列的一部分。 ## Spring Data JPA 派生的查詢 Spring Data JPA 可以從方法名稱創建查詢。這是約定而不是配置的特定形式。 Spring Data JPA 從具有屬性組合的特定關鍵字創建查詢；例如：`findByAgeLessThan`，`findByFirstnameEndingWith`或`findByFirstnameEquals`。關鍵字列表在 Spring Data JPA [文檔](https://docs.spring.io/spring-data/jpa/docs/current/reference/html/#jpa.query-methods.query-creation)中提供。 ## Spring Boot Data JPA 派生查詢示例以下應用使用兩個派生查詢。 ```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 ``` 這是項目結構。 `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 數據庫和 Spring Boot Data JPA 的依賴項。 `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，我們編寫了 Spring Boot 應用的各種配置設置。使用`spring.main.banner-mode`屬性，我們可以關閉 Spring 橫幅。 `spring.datasource.platform`設置數據庫的供應商名稱。在初始化腳本中使用它。 `spring.jpa.hibernate.ddl-auto`禁止從實體自動創建模式。 `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(); } } ``` 這是`City`實體。每個實體必須至少定義兩個注解：`@Entity`和`@Id`。 ```java @Entity @Table(name = "cities") public class City { ``` `@Entity`注解指定該類是一個實體，并映射到數據庫表。 `@Table`注解指定要用于映射的數據庫表的名稱。 ```java @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; ``` `@Id`注解指定實體的主鍵，`@GeneratedValue`提供規范主鍵值的生成策略。 `resources/schema-h2.sql` ```java CREATE TABLE cities(id INT PRIMARY KEY AUTO_INCREMENT, name VARCHAR(255), population INT); ``` 啟動應用時，將執行`schema-h2.sql`腳本。它創建一個新的數據庫表。 `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，執行`data-h2.sql`文件。它用數據填充表。 `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); } ``` 我們有兩種方法可以從中生成派生查詢。 ```java List<City> findByNameEndingWith(String ending); ``` 在這里，查詢將查找以指定字符串結尾的表單城市名稱。 ```java List<City> findByPopulationLessThan(int population); ``` 查詢將在其中查找人口少于指定數量的城市。 `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`提供了兩種簽約方法。 `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`包含服務方法實現。派生的查詢在`cityRepository`上調用。 `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`獲取所有人口少于一百萬的城市以及所有名稱以`"est"`結尾的城市。 `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`設置 Spring Boot 應用。 `@SpringBootApplication`啟用自動配置和組件掃描。 ```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}] ... ``` 我們運行該應用。在本教程中，我們使用了 Spring Data JPA 派生的查詢來獲取數據。您可能也對相關教程感興趣： * [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)。