无法获取任何字段

Question

我使用spring boot，带有jpa和hibernate

@Entity
@IdClass(SamplesPK.class)
public class Samples{
    ..
    @Id
    @ManyToOne
    @JoinColumns({
        @JoinColumn(name = "sampling_id", referencedColumnName = "id"),
        @JoinColumn(name = "sampling_year", referencedColumnName = "year")})
    private Samplings sampling;
    ...
}

@Entity
@IdClass(SamplingsPK.class)
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
public class Samplings {
    @OneToOne
    private Products product;
}

@Entity
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
public abstract class Products{
    ...
    @ManyToOne(fetch = FetchType.LAZY)
    private ProductTypes productType;
}

@Entity
@DiscriminatorValue("TraditionalProducts")
public class TraditionalProducts extends Products {
    ...
}

@Entity
@DiscriminatorValue("GranulateProducts")
public class GranulateProducts extends Products  {
     @ManyToMany(mappedBy="granulateProducts")
    private Set<Suppliers> suppliers = new HashSet<>();
}

 @Query(value = "select s from Samples s Join Fetch s.sampling sp Join Fetch sp.machine m Join Fetch sp.product p Join Fetch p.productType")
 public Page<Samples> findAllFullSample(Pageable pageable);

原因：org.hibernate.QueryException：查询指定的联接提取，但提取的关联的所有者不在选择列表[FromElement{explicit,not a collection join,fetch join,fetch non-lazy属性,ClassAlias=sp,Role=Com.lcm.Model.Samples.Samplings,TableName=Samplings,TableName=Samplings,TableAlias=Samplings,TableAlias=Samplings,TableAlias=Samplings1_,Origin=samples0_,Columns={

如果我删除了所有的fetch命令，它是工作的，为什么我不能使用fetch？

Answer 1

您可以在分页时使用fetch，但您将需要为count Row放置一个查询...

查看此帖子https://codingexplained.com/coding/java/spring-framework/fetch-query-not-working-spring-data-jpa-pageable#comment-293535