Join and inheritance with jpa / hibernate

Hibernate ORM
1

I use spring boot 2, postgresql with jpa and hibernate 5.2.17.
In my application I use inheritance.

public class Samples  extends BaseEntity{
    ..
    @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 extends  extends BaseEntity{
    @OneToOne
    private Products product;
}

@Entity
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
public abstract class Products  extends BaseEntity{
    ...
    @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<>();
}

@Entity
@DiscriminatorValue("GranulateSamplings")
public class GranulateSamplings extends Samplings{
    OneToOne(optional = true, fetch = FetchType.EAGER)
    @JoinColumn
    private Suppliers supplier;
    ...
}


public Page<Samples> advancedSearch(SamplesSearchDto search, Pageable page) {
     Specification<Samples> specification = (Root<Samples> root, CriteriaQuery<?> cq, CriteriaBuilder cb) -> {

         Predicate p = cb.conjunction();

         if (search.getProductsId() != null) {
             Join<Samples, Samplings> samplings = (Join) root.join("sampling");
             Join<Samples, Products> product = (Join) samplings.join("product");
             p.getExpressions().add(cb.equal(product.get("id"), search.getProductsId()));
         }

        if (search.getSuppliersId() != null) {
            Join<Samples, Samplings> samplings = (Join) root.join("sampling");
            Join<GranulateSamplings, Suppliers> supp = samplings.join("supplier");
            p.getExpressions().add(cb.equal(supp.get("id"), search.getSuppliersId()));
            //supplier name field is used in GranulateSamplings
        }

        return p;
    };

    return this.findAll(specification, page);
}

I get this error

Unable to locate Attribute with the the given name [supplier] on this ManagedType [com.lcm.model.Samplings]

It’s like inheritence is not see.

Edit

I saw type and treat but I was not able to get it working yet

2

The Samples base class does not have a supplier, so you need to write a separate query if you want to just select GranulateSamplings.