Specification API/Criteria API - Group by data returned by existing specification object and findAll(specification,pageable) - spring-boot

Question

Below are my entities:
Product
#Entity
#Table(name = "Product")
public class Product extends ReusableFields
{
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy = GenerationType.SEQUENCE)
Long productId;
#NonNull
#Column(name = "product_name")
String productName;
String measurementUnit;
//more fields and getters setters
}
Inward Outward List related to product:
#Entity
#Table(name = "inward_outward_entries")
public class InwardOutwardList extends ReusableFields
{
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
Long entryid;
#ManyToOne(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
#JoinColumn(name = "productId", nullable = false)
#JsonIgnoreProperties(
{ "hibernateLazyInitializer", "handler" })
Product product;
#JsonSerialize(using = DoubleTwoDigitDecimalSerializer.class)
Double quantity;
//more fields
}
Inward Inventory:
#Entity
#Table(name = "inward_inventory")
public class InwardInventory extends ReusableFields implements Cloneable
{
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#Column(name = "inwardid")
Long inwardid;
#ManyToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
#JoinTable(name = "inwardinventory_entry", joinColumns =
{ #JoinColumn(name = "inwardid", referencedColumnName = "inwardid") }, inverseJoinColumns =
{ #JoinColumn(name = "entryId", referencedColumnName = "entryId") })
Set<InwardOutwardList> inwardOutwardList = new HashSet<>();
//more fields
}
Inward Inventory Repo:
#Repository
public interface InwardInventoryRepo extends extends JpaRepository<InwardInventory, Long>, JpaSpecificationExecutor<InwardInventory> ,PagingAndSortingRepository<InwardInventory, Long>
{}
Previously the requirement was only to filter data and show as pages based on filters selected by user. So I have a working code to create specification dynamically based on inputs. It is working fine. After creating the specification, I am using:
Page<T> findAll(#Nullable Specification<T> spec, Pageable pageable);
to generate required list of records.
But, now a new requirement has been added to show sum of quantities grouped on product name and measurement unit. i.e. whatever data is returned after filter should be grouped by. Since the filtration logic is already working fine, I do not want to touch it.
Can somehow help how to reuse existing specification object and group the data returned by findall(specification,pageable) method.
What I already tried.
Since specification directly do not support group by, I autowired entity manager and created own criteria query. But this is not giving correct results as all the tables are getting joined twice. Might be because they are joined first during specification object and again during grouping by:
#Service
#Transactional
public class GroupBySpecification {
#Autowired
EntityManager entityManager;
Logger log = LoggerFactory.getLogger(GroupBySpecification.class);
public List<ProductGroupedDAO> findDataByConfiguration(Specification<InwardInventory> spec) {
CriteriaBuilder builder = entityManager.getCriteriaBuilder();
CriteriaQuery<ProductGroupedDAO> query = builder.createQuery(ProductGroupedDAO.class);
Root<T> root = query.from(InwardInventory.class);
Predicate p = spec.toPredicate(root, query, builder);
query.where(p);
Join< InwardInventory, InwardOutwardList> ioList = root.join(InwardInventory_.INWARD_OUTWARD_LIST);
Join<InwardOutwardList, Product> productList = ioList.join(InwardOutwardList_.PRODUCT);
query.multiselect(productList.get(Product_.PRODUCT_NAME), productList.get(Product_.MEASUREMENT_UNIT),
builder.sum(ioList.get(InwardOutwardList_.QUANTITY)));
query.groupBy(productList.get(Product_.PRODUCT_NAME), productList.get(Product_.MEASUREMENT_UNIT));
List<ProductGroupedDAO> groupedData = fetchData(query);
return groupedData;
}
Generated SQL - all the tables joined twice
SELECT DISTINCT product7_.product_name AS col_0_0_,
product10_.measurementunit AS col_1_0_,
Sum(inwardoutw12_.quantity) AS col_2_0_
FROM inward_inventory inwardinve0_
INNER JOIN inwardinventory_entry inwardoutw1_
ON inwardinve0_.inwardid = inwardoutw1_.inwardid
INNER JOIN inward_outward_entries inwardoutw2_
ON inwardoutw1_.entryid = inwardoutw2_.entryid
AND ( inwardoutw2_.is_deleted = 'false' )
INNER JOIN product product3_
ON inwardoutw2_.productid = product3_.productid
INNER JOIN warehouse warehouse4_
ON inwardinve0_.warehouse_id = warehouse4_.warehouse_id
INNER JOIN inwardinventory_entry inwardoutw5_
ON inwardinve0_.inwardid = inwardoutw5_.inwardid
INNER JOIN inward_outward_entries inwardoutw6_
ON inwardoutw5_.entryid = inwardoutw6_.entryid
AND ( inwardoutw6_.is_deleted = 'false' )
INNER JOIN product product7_
ON inwardoutw6_.productid = product7_.productid
INNER JOIN inwardinventory_entry inwardoutw8_
ON inwardinve0_.inwardid = inwardoutw8_.inwardid
INNER JOIN inward_outward_entries inwardoutw9_
ON inwardoutw8_.entryid = inwardoutw9_.entryid
AND ( inwardoutw9_.is_deleted = 'false' )
INNER JOIN product product10_
ON inwardoutw9_.productid = product10_.productid
INNER JOIN inwardinventory_entry inwardoutw11_
ON inwardinve0_.inwardid = inwardoutw11_.inwardid
INNER JOIN inward_outward_entries inwardoutw12_
ON inwardoutw11_.entryid = inwardoutw12_.entryid
AND ( inwardoutw12_.is_deleted = 'false' )
WHERE ( inwardinve0_.is_deleted = 'false' )
AND ( warehouse4_.warehousename LIKE ? )
AND ( product3_.product_name IN ( ?, ?, ?, ? ) )
GROUP BY product7_.product_name,
product10_.measurementunit

Answer 1

You will have to use the existing joins that are created by the specifications. You will probably have to do something like this:
public List<ProductGroupedDAO> findDataByConfiguration(Specification<InwardInventory> spec) {
CriteriaBuilder builder = entityManager.getCriteriaBuilder();
CriteriaQuery<ProductGroupedDAO> query = builder.createQuery(ProductGroupedDAO.class);
Root<T> root = query.from(InwardInventory.class);
Predicate p = spec.toPredicate(root, query, builder);
query.where(p);
Join< InwardInventory, InwardOutwardList> ioList = getOrCreateJoin(root, InwardInventory_.INWARD_OUTWARD_LIST);
Join<InwardOutwardList, Product> productList = getOrCreateJoin(ioList, InwardOutwardList_.PRODUCT);
query.multiselect(productList.get(Product_.PRODUCT_NAME), productList.get(Product_.MEASUREMENT_UNIT),
builder.sum(ioList.get(InwardOutwardList_.QUANTITY)));
query.groupBy(productList.get(Product_.PRODUCT_NAME), productList.get(Product_.MEASUREMENT_UNIT));
List<ProductGroupedDAO> groupedData = fetchData(query);
return groupedData;
}
<X, T> Join<X, T> getOrCreateJoin(From<?, X> from, SingularAttribute<X, T> attr) {
return from.getJoins().stream().filter(j -> j.getAttribute() == attr).findFirst().orElse(() -> from.join(attr));
}
<X, T> Join<X, T> getOrCreateJoin(From<?, X> from, PluralAttribute<X, ?, T> attr) {
return from.getJoins().stream().filter(j -> j.getAttribute() == attr).findFirst().orElse(() -> from.join(attr));
}