[FIXED] Spring JPA Specification One to Many Join 3 tables

Issue

I have 3 entities with the below relationships.

@Table(name = "a")
@Entity
public class A{
   @Id 
   @GeneratedValue
   @Column(name = "a_uuid")
   @OneToMany(mappedBy = "a", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
   private List<B> bList;

   @OneToMany(mappedBy = "a", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
   private List<C> cList;

}

@Table(name = "b")
@Entity
public class B{
   @ManyToOne(fetch = FetchType.LAZY)
   @JoinColumn(fetch = "a_uuid")
   private A a;
}

@Table(name = "c")
@Entity
class C{
   @ManyToOne(fetch = FetchType.LAZY)
   @JoinColumn(fetch = "a_uuid")
   private A a;
}

I need to join the above three tables and I am using a separate specification for each table

@Component
public class SpecificationTableAUtil {
    public Specification<A> tableACriteriaMatches(final SomeCriteria criteria) {
return (root, query, criteriaBuilder) -> {
            List<Predicate> predicateList = new ArrayList<>();
            predicateList .add(
                    criteriaBuilder.isNull(
                            root.get("some_column_in_table_a")));
            Predicate[] predicates = new Predicate[predicateList.size()];
            return criteriaBuilder.and(predicateList.toArray(predicates ));
        };
     }
   }
}

@Component
public class SpecificationTableBUtil {
    public Specification<A> tableBCriteriaMatches(final SomeCriteria criteria) {
return (root, query, criteriaBuilder) -> {
            ListJoin<A, B> b =
                root.joinList("bList", JoinType.LEFT);
            List<Predicate> predicateList = new ArrayList<>();
            predicateList .add(
                    criteriaBuilder.isNull(
                            b.get("some_column_in_table_b")));
            Predicate[] predicates = new Predicate[predicateList.size()];
            return criteriaBuilder.and(predicateList.toArray(predicates ));
        };
     }
   }
}

From my Service Class,

@Service
public class ServiceClass{
    //Autowire the utilities
    public Specification<A> getSpecification(final SomeCriteria criteria) {
            return bUtil.tableBCriteriaMatches(criteria)
                   .and(aUtil.tableACriteriaMatches(criteria));
     }
   }
}

Now I need to join Table C as well. How to implement this in a a better way? I need to have the lines of code per method to be as small as possible

Solution

I figured it out on my own. This is what I came up with.

@Component
public class SpecificationTableAUtil {

    @Autowired 
    private SpecificationTableBUtil bSpecificationUtil;

    public Specification<A> tableACriteriaMatches(final SomeCriteria criteria) {
return (root, query, criteriaBuilder) -> {
            List<Predicate> predicateList = new ArrayList<>();
            predicateList .add(
                    criteriaBuilder.isNull(
                            root.get("some_column_in_table_a")));
            predicateList.add(bSpecificationUtil.criteriaMatches(criteria).toPredicate(root, query, criteriaBuilder));
            Predicate[] predicates = new Predicate[predicateList.size()];
            return criteriaBuilder.and(predicateList.toArray(predicates ));
        };
     }
   }
}

For table B specification,

@Component
public class SpecificationTableBUtil {
    public Specification<A> tableBCriteriaMatches(final SomeCriteria criteria) {
return (root, query, criteriaBuilder) -> {
            ListJoin<A, B> b =
                root.joinList("bList", JoinType.LEFT);
            List<Predicate> predicateList = new ArrayList<>();
            predicateList .add(
                    criteriaBuilder.isNull(
                            b.get("some_column_in_table_b")));
            Predicate[] predicates = new Predicate[predicateList.size()];
            return criteriaBuilder.and(predicateList.toArray(predicates));
        };
     }
   }
}

From Service class,

@Service
public class ServiceClass {
   
    @Autowired
    private SpecificationTableAUtil aSpecificationUtil;
   
    public Specification<A> getSpecification(final SomeCriteria criteria) {
            return aSpecificationUtil.tableACriteriaMatches(criteria);
     }
   }
}

Answered By - Jammy