Spring-data-jpa扩展查询 QueryDSL 实践

说明: QueryDSL是以函数连接的方式将SQL调用进行拆分，比较spring data jpa中的criteria查询方法还是简洁了不少。 (转载请注明来源:cnblogs coder-fang)

用例:通过服务调用，使用querydsl进行查询并直接返回DTO对象(自定义传输对象(根据业务需求)，注意区别于Entity)

实践步骤:

1.　　创建user与depart表，使用外键进行关联，并插入一些模拟数据。

Spring-data-jpa扩展查询 QueryDSL 实践

2.　　创建sprintboot项目，在pom文件中加入以下依赖:

　　　　 <dependency>
            <groupId>com.querydsl</groupId>
            <artifactId>querydsl-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>com.querydsl</groupId>
            <artifactId>querydsl-apt</artifactId>
            <scope>provided</scope>
        </dependency>

3.　　在pom文件中<build>--><plugins>节点下加入plugin：

           <plugin>
                <groupId>com.mysema.maven</groupId>
                <artifactId>apt-maven-plugin</artifactId>
                <version>1.1.3</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>process</goal>
                        </goals>
                        <configuration>
                            <outputDirectory>target/generated-sources/java</outputDirectory>
                            <processor>com.querydsl.apt.jpa.JPAAnnotationProcessor</processor>
                        </configuration>
                    </execution>
                </executions>
                <dependencies>
                    <dependency>
                        <groupId>com.querydsl</groupId>
                        <artifactId>querydsl-apt</artifactId>
                        <version>4.1.3</version>
                    </dependency>
                </dependencies>
            </plugin>

4.　　生成相关entity与repository对象,这里以user为例:

package com.test.demo.db;
//

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import static javax.persistence.GenerationType.IDENTITY;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

/**
 * User generated by hbm2java
 */
@Entity
@Table(name = "user", catalog = "testdb")
public class User implements java.io.Serializable {

    private Integer id;
    private Department department;
    private String username;

    public User() {
    }

    public User(Department department, String username) {
        this.department = department;
        this.username = username;
    }

    @Id
    @GeneratedValue(strategy = IDENTITY)

    @Column(name = "id", unique = true, nullable = false)
    public Integer getId() {
        return this.id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "fk_depart")
    public Department getDepartment() {
        return this.department;
    }

    public void setDepartment(Department department) {
        this.department = department;
    }

    @Column(name = "username", length = 45)
    public String getUsername() {
        return this.username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

}

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