I'm not able to use Spring Data JPA projections and specifications together. I have the following setup:
Entity:
@Entity
public class Country {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
@Column(name = "NAME", nullable = false)
private String name;
@Column(name = "CODE", nullable = false)
private String code;
---getters & setters---
}
Projection Interface:
public interface CountryProjection {
String getName();
}
Country Specification:
public class CountrySpecification {
public static Specification<Country> predicateName(final String name) {
return new Specification<Country>() {
@Override
public Predicate toPredicate(Root<Country> eventRoot, CriteriaQuery<?> criteriaQuery, CriteriaBuilder criteriaBuilder) {
return criteriaBuilder.equal(eventRoot.get(Country_.name), name);
}
};
}
}
Repository:
public interface CountryRepository extends JpaRepository<Country, Long>, JpaSpecificationExecutor<Country> {
List<CountryProjection> findByName(String name); // works fine
List<CountryProjection> findAllProjectedBy(); // works fine
List<CountryProjection> findAllProjectedBy(Specification<Country> specification); //throws Exception as shown below
}
The first two methods findByName and findAllProjectedBy works fine. Whereas the third method findAllProjectedBy(Specification specification) throws the following exception -
Caused by: java.util.NoSuchElementException: null at java.util.ArrayList$Itr.next(ArrayList.java:854) ~[na:1.8.0_102] at java.util.Collections$UnmodifiableCollection$1.next(Collections.java:1042) ~[na:1.8.0_102] at org.springframework.data.jpa.repository.query.CriteriaQueryParameterBinder.bind(CriteriaQueryParameterBinder.java:63) ~[spring-data-jpa-1.10.6.RELEASE.jar:na] at org.springframework.data.jpa.repository.query.ParameterBinder.bind(ParameterBinder.java:100) ~[spring-data-jpa-1.10.6.RELEASE.jar:na] at org.springframework.data.jpa.repository.query.ParameterBinder.bindAndPrepare(ParameterBinder.java:160) ~[spring-data-jpa-1.10.6.RELEASE.jar:na] at org.springframework.data.jpa.repository.query.ParameterBinder.bindAndPrepare(ParameterBinder.java:151) ~[spring-data-jpa-1.10.6.RELEASE.jar:na] at org.springframework.data.jpa.repository.query.PartTreeJpaQuery$QueryPreparer.invokeBinding(PartTreeJpaQuery.java:218) ~[spring-data-jpa-1.10.6.RELEASE.jar:na] at org.springframework.data.jpa.repository.query.PartTreeJpaQuery$QueryPreparer.createQuery(PartTreeJpaQuery.java:142) ~[spring-data-jpa-1.10.6.RELEASE.jar:na] at org.springframework.data.jpa.repository.query.PartTreeJpaQuery.doCreateQuery(PartTreeJpaQuery.java:78) ~[spring-data-jpa-1.10.6.RELEASE.jar:na] at org.springframework.data.jpa.repository.query.AbstractJpaQuery.createQuery(AbstractJpaQuery.java:190) ~[spring-data-jpa-1.10.6.RELEASE.jar:na] at org.springframework.data.jpa.repository.query.JpaQueryExecution$CollectionExecution.doExecute(JpaQueryExecution.java:118) ~[spring-data-jpa-1.10.6.RELEASE.jar:na] at org.springframework.data.jpa.repository.query.JpaQueryExecution.execute(JpaQueryExecution.java:82) ~[spring-data-jpa-1.10.6.RELEASE.jar:na] at org.springframework.data.jpa.repository.query.AbstractJpaQuery.doExecute(AbstractJpaQuery.java:116) ~[spring-data-jpa-1.10.6.RELEASE.jar:na] at org.springframework.data.jpa.repository.query.AbstractJpaQuery.execute(AbstractJpaQuery.java:106) ~[spring-data-jpa-1.10.6.RELEASE.jar:na] at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.doInvoke(RepositoryFactorySupport.java:482) ~[spring-data-commons-1.12.6.RELEASE.jar:na] at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.invoke(RepositoryFactorySupport.java:460) ~[spring-data-commons-1.12.6.RELEASE.jar:na] at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.3.5.RELEASE.jar:4.3.5.RELEASE] at org.springframework.data.projection.DefaultMethodInvokingMethodInterceptor.invoke(DefaultMethodInvokingMethodInterceptor.java:61) ~[spring-data-commons-1.12.6.RELEASE.jar:na] at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.3.5.RELEASE.jar:4.3.5.RELEASE] at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:99) ~[spring-tx-4.3.5.RELEASE.jar:4.3.5.RELEASE] at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:282) ~[spring-tx-4.3.5.RELEASE.jar:4.3.5.RELEASE] at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:96) ~[spring-tx-4.3.5.RELEASE.jar:4.3.5.RELEASE] at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.3.5.RELEASE.jar:4.3.5.RELEASE] at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:136) ~[spring-tx-4.3.5.RELEASE.jar:4.3.5.RELEASE] at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.3.5.RELEASE.jar:4.3.5.RELEASE] at org.springframework.data.jpa.repository.support.CrudMethodMetadataPostProcessor$CrudMethodMetadataPopulatingMethodInterceptor.invoke(CrudMethodMetadataPostProcessor.java:133) ~[spring-data-jpa-1.10.6.RELEASE.jar:na] at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.3.5.RELEASE.jar:4.3.5.RELEASE] at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92) ~[spring-aop-4.3.5.RELEASE.jar:4.3.5.RELEASE] at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.3.5.RELEASE.jar:4.3.5.RELEASE] at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:213) ~[spring-aop-4.3.5.RELEASE.jar:4.3.5.RELEASE] at com.sun.proxy.$Proxy82.findAllProjectedBy(Unknown Source) ~[na:na] at com.mmp.data.jpa.DataJpaApplication.run(DataJpaApplication.java:42) [classes/:na] at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:800) [spring-boot-1.4.3.RELEASE.jar:1.4.3.RELEASE] ... 11 common frames omitted
How can this be achieved? Any ideas?
The ability to mix Projections and Specifications are not yet supported. There is a bug tracking this.
I found this https://github.com/pramoth/specification-with-projection and it seems to work which does exactly what you're looking for. I've included it in my own project and so far no problems. Big thanks to Pramoth.
Basically you extend JpaSpecificationExecutorWithProjection instead of JpaSpecificationExecutor.
public interface DocumentRepository extends JpaRepository< Country,Long>,JpaSpecificationExecutorWithProjection<Country,Long>
and you get findall() method with projections and specifications
<R> Page<R> findAll(Specification<T> spec, Class<R> projectionClass, Pageable pageable);
There is no solution unless you implement you own repository.
If you use Specification, you can't use in CountryRepository.
CountryRepository cRepository;
cRepository.findAll(Specification<Country> specification);
Another way you could solve this is by using the ProxyProjectionFactory. You would have your repository fetch the actual entity and then along the line (maybe in your service layer), map the resultset into the projection type. See below;
public interface CountryRepository extends JpaRepository<Country, Long>, JpaSpecificationExecutor<Country> {
}
then in your service, you do this;
List<CountryProjection> findAllProjectedBy(Specification<Country> countrySpecification) {
List<Country> countries = this.countryRepository.findAll(countrySpecification);
ProxyProjectionFactory pf= new SpelAwareProxyProjectionFactory();
return countries.stream().map(c->pf.createProjection(CountryProjection.class, c)).collect(Collectors.toList());
}
Hope this helps!
@esdee: For now, I Created a Custom Repository Implementation where I created a dynamic query where you can create even a native query and map it to a DTO without using projections.
In order to do this you can see this doc:
Here is a already example:
Spring Data JPA Custom Repository
Just keep in mind that if you want to make it pageable, in your Custom Repository you have to create also a method to count the rows, that you want to extract in your customFindAll(parameters). The disadgantage is that I rewrote the specifications in native query. But maybe the custom Implmentation can work also with Specification, let me know if it helps.
Regards, C
来源：https://stackoverflow.com/questions/41692391/how-to-use-projections-and-specifications-with-spring-data-jpa