Java JPQL 限制查询
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JPQL limit query
提问by user3115056
How can I limit in a select query of JPQL named query? I need the limit to be done in the query level itself and not in the java layer!!! I am trying to use
如何限制 JPQL 命名查询的选择查询？我需要在查询级别本身而不是在java层中完成限制！！！我正在尝试使用
@NamedQueries(value = {
@NamedQuery(name = UserNotification.QueryName.NOTIFICATION_DISPLAYED,
query = "SELECT un FROM UserNotification un " +
"WHERE un.orgId IN (:orgList) " +
"AND un.user.id = :userId LIMIT 5")
but in vain!!!
但徒劳无功！！！
Please suggest
请建议
采纳答案by Kevin Bowersox
JPQLdoes not provide a mechanism to limit queries. This is most often achieved by using the setMaxResults()method on the Query. If you must avoid specifying this in Java code, you could make a view in the database that contains your query and performs the limit. Then map an entity to this view as you would a table.
JPQL不提供限制查询的机制。这通常是通过使用 上的setMaxResults()方法来实现的Query。如果您必须避免在 Java 代码中指定此项，您可以在包含您的查询的数据库中创建一个视图并执行限制。然后像映射表一样将实体映射到此视图。
Example:
例子：
List<String> resultList= query.setMaxResults(100).getResultList();
回答by Udit Agarwal
while executing the query with entity manager just write .setMaxResults(no of obj)
在使用实体管理器执行查询时，只需编写 .setMaxResults(no of obj)
回答by muttonUp
For specific @NamedQueries where a limit is required, you can switch to @NamedNativeQuery
对于需要限制的特定@NamedQueries，您可以切换到@NamedNativeQuery
@NamedNativeQuery(
name=UserNotification.QueryName.NOTIFICATION_DISPLAYED_LIMIT5,
query="SELECT un.* FROM user_notification un " +
"WHERE un.user.id = ?1 LIMIT 5",
resultClass=UserNotification.class
)
Not quite as smooth, but does the job.
不太顺利，但可以完成工作。
回答by George Siggouroglou
In case you are working with spring-datayou should use the Pageable Interface. A sample code below,
如果您正在使用spring-data，您应该使用Pageable Interface。下面的示例代码，
My Service,
我的服务，
import org.springframework.data.domain.Page;
import org.springframework.data.domain.PageRequest;
@Service
public class MyModelService {
@Autowired
private MyModelRepository myModelRepository;
@Transactional
public Page<MyModel> findMyModelTop5() {
return myModelRepository.findMyModelTop5(new PageRequest(0, 5));
}
}
My Repository,
我的存储库，
import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
@Repository
public interface MyModelRepository extends JpaRepository<MyModel, Integer> {
@Query("SELECT mm FROM MyModel mm")
public Page<MyModel> findMyModelTop5(Pageable pageable);
}
You can find a more complete answer about the spring data available options here.
您可以在此处找到有关弹簧数据可用选项的更完整答案。
