Spring Boot Data JPA @NamedQuery 教程|极客教程

Spring Boot Data JPA @NamedQuery 教程展示了如何使用 JPA @NamedQuery 创建自定义查询。

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。

JPA `@NamedQuery`

@NamedQuery注解是我们创建的预定义查询，并与容器管理的实体相关联。 @Query注解是类似的注解，它直接在存储库方法上声明查找程序查询。在域类上使用@NamedQuery时，在 Repository 接口上使用 Spring Data JPA @Query 注解。这样可以将域类从持久性特定的信息中解放出来，这是一件好事。

Spring Boot Data JPA @NamedQuery 示例

以下应用是一个简单的 Spring Boot Web 应用，它使用 JPA @NamedQuery 创建一个自定义查询。该示例的数据存储在基于内存的 H2 数据库中。数据库在应用启动时初始化。

pom.xml
src
├───main
│   ├───java
│   │   └───com
│   │       └───zetcode
│   │           │   Application.java
│   │           ├───controller
│   │           │       MyController.java
│   │           ├───model
│   │           │       City.java
│   │           ├───repository
│   │           │       CityRepository.java
│   │           └───service
│   │                   CityService.java
│   │                   ICityService.java
│   └───resources
│       │   application.properties
│       │   data-h2.sql
│       │   schema-h2.sql
│       ├───static
│       │       index.html
│       └───templates
│               showCities.ftl
└───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>springbootdatajpanamedquery</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>com.h2database</groupId>
            <artifactId>h2</artifactId>
            <scope>runtime</scope>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-freemarker</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </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，Freemarker 和 Spring Boot Data JPA 的依赖项。

resources/application.properties

spring.main.banner-mode=off
spring.datasource.platform=h2
logging.level.org.hibernate.SQL=DEBUG
spring.jpa.show-sql=true
spring.jpa.hibernate.ddl-auto=none

在application.properties文件中，我们有各种配置设置。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.show-sql允许记录 SQL 语句。最后，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.NamedQuery;
import javax.persistence.Table;

@Entity
@Table(name = "cities")
@NamedQuery(name = "City.findAllOrderedByNameDescending",
        query = "SELECT c FROM City c ORDER BY c.name DESC")
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。它包含一个命名查询。

@Entity
@Table(name = "cities")
@NamedQuery(name = "City.findAllOrderedDescending",
        query = "SELECT c FROM City c ORDER BY c.name DESC")
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。 @NamedQuery定义了一个命名查询，该查询返回按名称降序排列的所有城市。

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);

之后，执行data-h2.sql文件。它用数据填充表。

com/zetcode/CityRepository.java

package com.zetcode.repository;

import com.zetcode.model.City;
import java.util.List;
import org.springframework.data.repository.CrudRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface CityRepository extends CrudRepository<City, Long> {

    List<City> findAllOrderedByNameDescending();
}

我们将findAllOrderedByNameDescending()的声明添加到存储库接口中。

com/zetcode/service/ICityService.java

package com.zetcode.service;

import com.zetcode.model.City;
import java.util.List;

public interface ICityService {

    List<City> findAllOrderedByNameDescending();
}

ICityService包含一种合同方法，用于按名称降序排列所有城市。

com/zetcode/service/CityService.java

package com.zetcode.service;

import com.zetcode.model.City;
import com.zetcode.repository.CityRepository;
import java.util.List;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class CityService implements ICityService {

    @Autowired
    private CityRepository repository;

    @Override
    public List<City> findAllOrderedByNameDescending() {

        var cities = (List<City>) repository.findAllOrderedByNameDescending();
        return cities;
    }
}

CityService包含findAllOrderedByNameDescending()方法的实现。我们使用存储库从数据库检索数据。

com/zetcode/controller/MyController.java

package com.zetcode.controller;

import com.zetcode.model.City;
import com.zetcode.service.ICityService;
import java.util.List;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.GetMapping;

@Controller
public class MyController {

    @Autowired
    private ICityService cityService;

    @GetMapping("/showCities")
    public String findAllOrderedByNameDescending(Model model) {

        var cities = (List<City>) cityService.findAllOrderedByNameDescending();

        model.addAttribute("cities", cities);

        return "showCities";
    }
}

MyController类用@Controller注解。

@Autowired
private ICityService cityService;

我们在countryService字段中插入ICityService。

@GetMapping("/showCities")
public String findAllOrderedByNameDescending(Model model) {

    var cities = (List<City>) cityService.findAllOrderedByNameDescending();

    System.out.println(cities);

    model.addAttribute("cities", cities);

    return "showCities";
}

我们将带有showCities路径的请求映射到控制器的findAllOrderedByNameDescending()方法。该模型将获得按名称降序排列的城市列表，并将处理发送到showCities.ftl Freemarker 模板文件。

resources/templates/showCities.ftl

<!DOCTYPE html>
<html>
    <head>
        <title>Cities</title>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        </head>
    <body>
        <h2>List of cities ordered by name in descending order</h2>

        <table>
            <tr>
                <th>Id</th>
                <th>Name</th>
                <th>Population</th>
            </tr>

            <#list cities as city>
                <tr>
                    <td>{city.id}</td>
                    <td>{city.name}</td>
                    <td>${city.population}</td>
                </tr>
            </#list>
        </table>
    </body>
</html>

在showCities.ftl模板文件中，我们在 HTML 表中显示数据。

resources/static/index.html

<!DOCTYPE html>
<html>
    <head>
        <title>Home page</title>
        <meta charset="UTF-8"/>
        <meta name="viewport" content="width=device-width, initial-scale=1.0"/>
    </head>
    <body>
        <a href="showCities">Show ordered cities by name in descending order</a>
    </body>
</html>

在index.html中有一个链接，显示订购的城市。

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);
    }
}