Querydsl-JPA learning (Beginners)

1.Querydsl-JPA Description:

Springdata-JPA JPA is used for packaging, Querydsl-JPA query is based on a common framework on a variety of the ORM, using its API library can write "the Java code sql", without manual contact sql statement to express the meaning is as accurate as sql. More to the point, it is possible to build secure type of inquiry, which compared the use of JPA is very different from when native queries, we can no longer have to disgusting "Object []" carried out the operation. Of course, we can SpringDataJPA + Querydsl-JPA joint use, has a perfect mutual support between them, in order to achieve more efficient coding.

gitub Address: github.com/querydsl/qu...

2.spring boot configuration Querydsl-JPA:

2.1: New jar package:

 <dependency>
            <groupId>com.querydsl</groupId>
            <artifactId>querydsl-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>com.querydsl</groupId>
            <artifactId>querydsl-apt</artifactId>
            <scope>provided</scope>
        </dependency>
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2.2: New plugin:

Action: generating a Q-entity classes of entity class annotated with @Entity

 <!-- query dsl 构建Q版实体类的插件-->
            <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>
            </plugin>
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2.3: JPAQueryFactory configuration:

Effect: when using QueryDSL features, will depend on the use to JPAQueryFactory, and rely on the use EntityManager JPAQueryFactory herein, it is done as follows in the main category, so we inject EntityManager Spring automatically help and automatic management JPAQueryFactory

import javax.persistence.EntityManager;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
import com.querydsl.jpa.impl.JPAQueryFactory;
@Configuration
public class WebMvcConfig implements WebMvcConfigurer {    
    @Bean
    public JPAQueryFactory jpaQuery(EntityManager entityManager) {
        return new JPAQueryFactory(entityManager);
    }
}    
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2.4: Use bean injection:

    @Autowired
    private JPAQueryFactory jpaQueryFactory;
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2.5: maven build operation:

3.Querydsl-JPA single-table operation:

3.1 new entity classes:

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import org.hibernate.annotations.GenericGenerator;

import javax.persistence.*;
import java.math.BigDecimal;
import java.sql.Timestamp;

@AllArgsConstructor
@NoArgsConstructor
@Data
@Entity
@Table(name = "user_tmw")
@JsonIgnoreProperties({"hibernateLazyInitializer", "handler"})
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO, generator = "custom-uuid")
    @GenericGenerator(name = "custom-uuid", strategy = "com.springboot.demo.bean.CustomUUIDGenerator")
    @Column(name = "id", nullable = false, length = 32)
    private String id;

    @Column(name = "name", length = 10)
    private String name;

    @Column(name = "age")
    private Integer age;

    @Column(name = "money")
    private BigDecimal money;

    @Column(name = "begin_time")
    private Timestamp beginTime;

    @Column(name = "end_time")
    private Timestamp endTime;
}
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3.2 The results set equal to a value of:

    QUser user = QUser.user;
    //单表获取年龄为10的结果集
    List<User> ageList = jpaQueryFactory.selectFrom(user).where(user.age.eq(10)).fetch();
    String ageListStr = JSON.toJSONString(ageList);
    System.out.println("单表获取年龄为10的结果集:"+ageListStr);

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3.3 is equal to a value of a single query: fetchFirst usage:

    QUser user = QUser.user;
    //fetchFirst的用法： 单表获取年龄为10的首个结果
    User user1 = jpaQueryFactory.selectFrom(user).where(user.age.eq(10)).fetchFirst();
    System.out.println("单表获取年龄为10的首个结果:"+user1.toString());

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3.4 Use fuzzy search of 1 (like keyword):

    QUser user = QUser.user;
    //模糊检索的用法：单表获取名称包含小的用户并且按照年龄倒排序
    List<User> nameList = jpaQueryFactory.selectFrom(user).where(user.name.like("%小%")).orderBy(user.age.desc()).fetch();
    String nameListStr = JSON.toJSONString(nameList);
    System.out.println("单表获取名称包含小的用户并且按照年龄倒排序的结果集:"+nameListStr);

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3.5 fuzzy search usage 2 (startsWith):

    QUser user = QUser.user;
    //模糊检索的用法：单表获取名称是以小开头的用户并且按照年龄正序排
    List<User> nameAscList = jpaQueryFactory.selectFrom(user).where(user.name.startsWith("小")).orderBy(user.age.asc()).fetch();
    String nameAscListStr = JSON.toJSONString(nameAscList);
    System.out.println("单表获取名称是以小开头的用户并且按照年龄正序排的结果集:"+nameAscListStr);
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3.6 Usage range (between):

    QUser user = QUser.user;
    //between 区间的用法：单表获取开始时间是XX-XX 区间的用户
    String time = "2019-07-22 00:00:00";
    SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    Date date= df.parse(time);
    Timestamp nousedate = new Timestamp(date.getTime());

    String time1 = "2019-07-23 00:00:00";
    Date date1= df.parse(time1);
    Timestamp nousedate1 = new Timestamp(date1.getTime());

    List<User> beginTimeList = jpaQueryFactory.selectFrom(user).where(user.beginTime.between(nousedate, nousedate1)).fetch();
    String beginTimeListStr = JSON.toJSONString(beginTimeList);
    System.out.println("单表获取开始时间是XX-XX 区间的用户的结果集:"+beginTimeListStr);

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3.7 in usage:

    QUser user = QUser.user;
    //in 的用法：单表获取年龄是10,20的用户
    List<Integer> ageLists = new ArrayList<>();
    ageLists.add(10);
    ageLists.add(20);
    List<User> ages = jpaQueryFactory.selectFrom(user).where(user.age.in(ageLists)).fetch();
    String agesStr = JSON.toJSONString(ages);
    System.out.println("单表获取年龄是10,20的用户的结果集:"+agesStr);

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3.8 aggregation function max, avg, min usage:

    QUser user = QUser.user;
    //聚合函数-concat()的使用：单表查询将用户id，名称，年龄拼接的结果
    List<String> concatList = jpaQueryFactory.select(user.id.concat(user.name).concat(user.age.stringValue())).from(user).fetch();
    String concatListStr = JSON.toJSONString(concatList);
    System.out.println("单表查询将用户id，名称，年龄拼接的结果:"+concatListStr);

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3.9 aggregate functions groupby usage:

    QUser user = QUser.user;
    List<Map<String,Object>> tupleJPAQuery = jpaQueryFactory.select(user.age, user.count().as("count")).from(user).groupBy(user.age)
        .fetch().stream().map(x->{
            Map<String,Object> resultMap = new HashMap<>();
            resultMap.put("age",x.get(0,QUser.class));
            resultMap.put("count",x.get(1,QUser.class));
            return resultMap;
        }).collect(Collectors.toList());
    
    String userQueryResultsStr = JSON.toJSONString(tupleJPAQuery);
    System.out.println("单表分组的结果集:"+userQueryResultsStr);
    
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More than 3.10 splicing condition of use (BooleanBuilder):

    QUser user = QUser.user;
    //多条件处理
    BooleanBuilder booleanBuilder = new BooleanBuilder();
    booleanBuilder.and(user.age.eq(10));
    booleanBuilder.and(user.name.contains("小"));
    List<User> mostlist = jpaQueryFactory.selectFrom(user).where(booleanBuilder).fetch();
    String mostlistStr = JSON.toJSONString(mostlist);
    System.out.println("单表查询多条件处理的结果:"+mostlistStr);

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3.11 paging query processing:

    QUser user = QUser.user;
    QueryResults<User> userQueryResults =
    jpaQueryFactory.selectFrom(user).offset(0).limit(2).fetchResults();
    String userQueryResultsStr = JSON.toJSONString(userQueryResults);
    System.out.println("单表分页的结果集:"+userQueryResultsStr);

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