How to use projection interfaces with pagination i

问题:

I'm trying to get a page of a partial entity (NetworkSimple) using the new feature of spring data, projections

I've checked the documentation and if I request only:

Collection<NetworkSimple> findAllProjectedBy();

It works, but if I'm using pageable:

Page<NetworkSimple> findAllProjectedBy(Pageable pageable);

It throws an error:

org.hibernate.jpa.criteria.expression.function.AggregationFunction$COUNT cannot be cast to org.hibernate.jpa.criteria.expression.CompoundSelectionImpl

Any one has already work with this ?

My NetworkSimple class is the following:

public interface NetworkSimple {
    Long getId();

    String getNetworkName();

    Boolean getIsActive();
}

回答1:

Note: This feature should work in the way described by the original poster but due to this bug it didn't. The bug has been fixed for the Hopper SR2 release, if you're stuck on an earlier version then the workaround below will work.

It is possible to use Pageable with the new query projection features introduced in Spring Data JPA 1.10 (Hopper). You will need to use the @Query annotation and manually write a query for the fields you require, they must also be aliased using AS to allow Spring Data to figure out how to project the results. There is a good example in spring-boot-samples part of the spring boot repository.

In your example it would be quite simple:

@Query("SELECT n.id AS id, n.name AS networkName, n.active AS isActive FROM Network n")
Page<NetworkSimple> findAllProjectedBy(Pageable pageable);

I have made the assumption that your entity looks something like this:

@Entity
public class Network
{
    @Id
    @GeneratedValue
    private Long id;

    @Column
    private String name;

    @Column
    private boolean active;

    ...
}

Spring Data will derive a count query automatically for the paging information. It is also possible to make use of joins in the query to fetch associations and then summarise them in the projection.

回答2:

The issue may come from the method name. The by keyword means that you ae filterig data by a specific property: findByName for example. Its called query creation from method name:

http://docs.spring.io/spring-data/jpa/docs/1.10.1.RELEASE/reference/html/#repositories.query-methods.query-creation

So try with Page<NetworkSimple> findAll(Pageable pageable);

回答3:

I think you need create findAllProjectedBy() as specification.Then you can use findAll() method like this.

example :findAll(findAllProjectedBy(),pageable)

Following link may be help to find how to create specification in spring.

https://spring.io/blog/2011/04/26/advanced-spring-data-jpa-specifications-and-querydsl/

回答4:

You can use:

@Query("SELECT n FROM Network n")
Page<? extends NetworkSimple> findAllProjectedBy(Pageable pageable);

回答5:

Even with spring-data-jpa 1.11.4, something like

public interface NetworkRepository extends JpaRepository<Network, String> {
    Page<NetworkSimple> findAll(Pageable pageable);
}

would not compile; reporting

findAll(org.springframework.data.domain.Pageable) in NetworkRepository clashes with findAll(org.springframework.data.domain.Pageable) in org.springframework.data.repository.PagingAndSortingRepository
return type org.springframework.data.domain.Page<NetworkSimple> is not compatible with org.springframework.data.domain.Page<Network>

The workaround we found was to rename findAll to findAllBy, e.g.

public interface NetworkRepository extends JpaRepository<Network, String> {
    Page<NetworkSimple> findAllBy(Pageable pageable);
}

回答6:

You can use interface projection with Pageable like this :

Page<NetworkSimple> findPagedProjectedBy(Pageable pageable);

with some parameter :

Page<NetworkSimple> findPagedProjectedByName(String name, Pageable pageable);