QueryDSL-JPA
QueryDSL簡介
1 QueryDSL僅僅是一個通用的查詢框架，專注於通過Java API構建類型安全的SQL查詢。
2 Querydsl可以通過一組通用的查詢API為用戶構建出適合不同類型ORM框架或者是SQL的查詢語句，也就是說QueryDSL是基於各種ORM框架以及SQL之上的一個通用的查詢框架。
3 借助QueryDSL可以在任何支持的ORM框架或者SQL平台上以一種通用的API方式來構建查詢。目前QueryDSL支持的平台包括JPA,JDO,SQL,Java Collections,RDF,Lucene,Hibernate Search。
創建項目
首先對於queryDSL有兩個版本,com.mysema.querydsl和com.querydsl,前者是3.X系列后者是4.X系列,這里使用的是后者.
第一步:Maven引入依賴
<!--query dsl-->
<dependency>
<groupId>com.querydsl</groupId>
<artifactId>querydsl-jpa</artifactId>
<version>${querydsl.version}</version>
</dependency>
<dependency>
<groupId>com.querydsl</groupId>
<artifactId>querydsl-apt</artifactId>
<version>${querydsl.version}</version>
<scope>provided</scope>
</dependency>
<!--query dsl end-->
第二步:加入插件,用於生成查詢實例
<!--該插件可以生成querysdl需要的查詢對象，執行mvn compile即可-->
<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>
執行mvn compile之后,可以找到該target/generated-sources/java,然后IDEA標示為源代碼目錄即可.
實體類
城市類:
@Entity
@Table(name = "t_city", schema = "test", catalog = "")
public class TCity {
//省略JPA注解標識
private int id;
private String name;
private String state;
private String country;
private String map;
}
旅館類:
@Entity
@Table(name = "t_hotel", schema = "test", catalog = "")
public class THotel {
//省略JPA注解標識
private int id;
private String name;
private String address;
private Integer city;//保存着城市的id主鍵
}
單表動態分頁查詢
Spring Data JPA中提供了QueryDslPredicateExecutor接口,用於支持QueryDSL的查詢操作,這樣的話單表動態查詢就可以參考如下代碼:
//查找出Id小於3,並且名稱帶有`shanghai`的記錄.
//動態條件
QTCity qtCity = QTCity.tCity;
//該Predicate為querydsl下的類,支持嵌套組裝復雜查詢條件
Predicate predicate = qtCity.id.longValue().lt(3)
.and(qtCity.name.like("shanghai"));
//分頁排序
Sort sort = new Sort(new Sort.Order(Sort.Direction.ASC,"id"));
PageRequest pageRequest = new PageRequest(0,10,sort);
//查找結果
Page<TCity> tCityPage = tCityRepository.findAll(predicate,pageRequest);
多表動態查詢
QueryDSL對多表查詢提供了一個很好地封裝,看下面代碼:
/**
* 關聯查詢示例,查詢出城市和對應的旅店
* @param predicate 查詢條件
* @return 查詢實體
*/
@Override
public List<Tuple> findCityAndHotel(Predicate predicate) {
JPAQueryFactory queryFactory = new JPAQueryFactory(em);
JPAQuery<Tuple> jpaQuery = queryFactory.select(QTCity.tCity,QTHotel.tHotel)
.from(QTCity.tCity)
.leftJoin(QTHotel.tHotel)
.on(QTHotel.tHotel.city.longValue().eq(QTCity.tCity.id.longValue()));
//添加查詢條件
jpaQuery.where(predicate);
//拿到結果
return jpaQuery.fetch();
}
城市表左連接旅店表,當該旅店屬於這個城市時查詢出兩者的詳細字段,存放到一個Tuple的多元組中.相比原生sql,簡單清晰了很多.
那么該怎么調用這個方法呢?
@Test
public void findByLeftJoin(){
QTCity qtCity = QTCity.tCity;
QTHotel qtHotel = QTHotel.tHotel;
//查詢條件
Predicate predicate = qtCity.name.like("shanghai");
//調用
List<Tuple> result = tCityRepository.findCityAndHotel(predicate);
//對多元組取出數據,這個和select時的數據相匹配
for (Tuple row : result) {
System.out.println("qtCity:"+row.get(qtCity));
System.out.println("qtHotel:"+row.get(qtHotel));
System.out.println("--------------------");
}
System.out.println(result);
}
這樣做的話避免了返回Object[]數組,下面是自動生成的sql語句:
select
tcity0_.id as id1_0_0_,
thotel1_.id as id1_1_1_,
tcity0_.country as country2_0_0_,
tcity0_.map as map3_0_0_,
tcity0_.name as name4_0_0_,
tcity0_.state as state5_0_0_,
thotel1_.address as address2_1_1_,
thotel1_.city as city3_1_1_,
thotel1_.name as name4_1_1_
from
t_city tcity0_
left outer join
t_hotel thotel1_
on (
cast(thotel1_.city as signed)=cast(tcity0_.id as signed)
)
where
tcity0_.name like ? escape '!'
多表動態分頁查詢
分頁查詢對於queryDSL無論什么樣的sql只需要寫一遍,會自動轉換為相應的count查詢,也就避免了文章開始的問題4,下面代碼是對上面的查詢加上分頁功能:
@Override
public QueryResults<Tuple> findCityAndHotelPage(Predicate predicate,Pageable pageable) {
JPAQueryFactory queryFactory = new JPAQueryFactory(em);
JPAQuery<Tuple> jpaQuery = queryFactory.select(QTCity.tCity.id,QTHotel.tHotel)
.from(QTCity.tCity)
.leftJoin(QTHotel.tHotel)
.on(QTHotel.tHotel.city.longValue().eq(QTCity.tCity.id.longValue()))
.where(predicate)
.offset(pageable.getOffset())
.limit(pageable.getPageSize());
//拿到分頁結果
return jpaQuery.fetchResults();
}
和上面不同之處在於這里使用了offset和limit限制查詢結果.並且返回一個QueryResults,該類會自動實現count查詢和結果查詢,並進行封裝.
調用形式如下:
@Test
public void findByLeftJoinPage(){
QTCity qtCity = QTCity.tCity;
QTHotel qtHotel = QTHotel.tHotel;
//條件
Predicate predicate = qtCity.name.like("shanghai");
//分頁
PageRequest pageRequest = new PageRequest(0,10);
//調用查詢
QueryResults<Tuple> result = tCityRepository.findCityAndHotelPage(predicate,pageRequest);
//結果取出
for (Tuple row : result.getResults()) {
System.out.println("qtCity:"+row.get(qtCity));
System.out.println("qtHotel:"+row.get(qtHotel));
System.out.println("--------------------");
}
//取出count查詢總數
System.out.println(result.getTotal());
}
生成的原生count查詢sql,當該count查詢結果為0的話,則直接返回,並不會再進行具體數據查詢:
select
count(tcity0_.id) as col_0_0_
from
t_city tcity0_
left outer join
t_hotel thotel1_
on (
cast(thotel1_.city as signed)=cast(tcity0_.id as signed)
)
where
tcity0_.name like ? escape '!'
生成的原生查詢sql:
select
tcity0_.id as id1_0_0_,
thotel1_.id as id1_1_1_,
tcity0_.country as country2_0_0_,
tcity0_.map as map3_0_0_,
tcity0_.name as name4_0_0_,
tcity0_.state as state5_0_0_,
thotel1_.address as address2_1_1_,
thotel1_.city as city3_1_1_,
thotel1_.name as name4_1_1_
from
t_city tcity0_
left outer join
t_hotel thotel1_
on (
cast(thotel1_.city as signed)=cast(tcity0_.id as signed)
)
where
tcity0_.name like ? escape '!' limit ?
查看打印,可以發現對應的city也都是同一個對象,hotel是不同的對象.