Spring Boot Data JPA 查询示例|极客教程

Spring Boot Data JPA Query By Example 教程展示了如何使用 Spring Data JPA Query By Example 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）是一种具有简单界面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。

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

<?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

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 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。 spring.jpa.hibernate.ddl-auto禁止从实体自动创建模式。

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。每个实体必须至少定义两个注解：@Entity和@Id。

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('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

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

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

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。

var city = new City();
city.setName(ending);

我们有一个City域对象。这称为探针。

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。

var example = Example.of(city, matcher);

根据域对象和匹配器创建一个Example。

return (List<City>) cityRepository.findAll(example);

Example传递给findAll()方法。

com/zetcode/MyRunner.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“布拉迪斯拉发”和“柏林”城市，并找到所有名称以“ est”结尾的城市。

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
...
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}]
...