We Keep Coding

Order By in JPQL query on a #ElementCollection annotated map

In my #Entity annotated Course class, I have the following #ElementCollection annotated map:
#ElementCollection
private Map<Student, Double> courseStudAndAvgStudGrade;
In the example above, Student is another #Entity annotated class and the value is the average grade from a Course for each Student. I'm trying to write a query in JPQL that would retrieve all the entries of this map and sort by entry value in descending order.
So far, I have the following:
TypedQuery<Tuple> query =
em.createQuery("SELECT KEY(map), VALUE(map) "
+ "FROM Course c JOIN c.courseStudAndAvgStudGrade map WHERE c.id = :id", Tuple.class);
This retrieves the values correctly in a Tuple for the desired Course, however adding ORDER BY VALUE(map) DESC to the JPQL query results in a java.sql.SQLException: Subquery returns more than 1 row.
Is it possible to do ORDER BY on a map in JPQL?

JPA/Hibernate does not require the VALUE qualifier i.e. it's actually just there for completeness. Try the following query:
em.createQuery("SELECT KEY(map), map FROM Course c JOIN c.courseStudAndAvgStudGrade map WHERE c.id = :id ORDER BY map DESC", Tuple.class);

Hibernate doesn't return proper objects in inner join

I'm working on Spring MVC application that uses Hibernate. One of my requests in SQL looks like this:
SELECT work_order.* FROM work_order
inner join user
on
work_order.user_id = user.id
and
user.user_name = 'Jenna'
and I do get a result as a row of workorders. When I'm trying to do the same with Hibernate I get five objects(which is correct) but can't convert into WorkoOrder objects.
Here's my Hibernate request:
List<WorkOrder> workorders = (List<WorkOrder>)currentSession.createQuery(
"from WorkOrder w inner join w.user as u where user_name=:tempName")
.setParameter("tempName", tempName).getResultList();
Where tempName is a parameter. I do get objects, but can't cast them to Workorder, probably because Hibernate returns Workorders and Users combined. How to fix this so only Workorders will be returned?
Update: User is mapped in WorkOrder
#ManyToOne(fetch = FetchType.EAGER)
#JoinColumn(name="user_id", nullable = true)
private User user;

Your HQL does not have a select clause. If you want only the WorkOrder entities from the join you form, then you'll need to tell Hibernate so:
currentSession.createQuery(
"select w from WorkOrder w inner join w.user as u where u.user_name=:tempName")

Named entity graph JOINS results (need distinct option) in Spring Data JPA

I'm using #NamedEntityGraph annotation to load a graph from database.
#NamedEntityGraph(
name = "Firma.uredjivanje",
attributeNodes = {
#NamedAttributeNode(value="prevodi", subgraph = "prevodi")
},
subgraphs = {
#NamedSubgraph(
name = "prevodi",
attributeNodes = {
#NamedAttributeNode(value = "jezik", subgraph = "jezik")
}
)
}
)
In the Spring Data JPA repository, I'm using annotation:
#EntityGraph(value="Firma.uredjivanje", type = EntityGraph.EntityGraphType.LOAD)
List<Firma> getByAktivna(boolean aktivna);
Everything works as expected, expect that all relations are joined, and I get duplicate Firma entities (because of JOIN). Instead of a List with entity id's {1,2,3}, I get {1,1,1,2,2,3}.
What is the best way to get distinct entities (if this is not a bug ofcourse).

Found the answer... Since NamedEntityGraph does JOIN in database, it selects all entities without DISTINCT. So the solution is to use Distinct in method name...
#EntityGraph(value="Firma.uredjivanje", type = EntityGraph.EntityGraphType.LOAD)
List<Firma> getDistinctByAktivna(boolean aktivna);

After adding dictinct I have error logs during server starup (maybe because there is no such thing as findDistinctAll() .
For me help a hint in https://jira.spring.io/browse/DATAJPA-680.
I added #Query annotation to the method, so my method looks like below
#EntityGraph(value = "User.detail", type = EntityGraph.EntityGraphType.LOAD)
#Query(value = "SELECT DISTINCT u FROM User u")
List<User> findAll();

Order by count using Spring Data JpaRepository

I am using Spring Data JpaRepository and I find it extremely easy to use. I actually need all those features - paging, sorting, filtering. Unfortunately there is one little nasty thing that seems to force me to fall back to use of plain JPA.
I need to order by a size of associated collection. For instance I have:
#Entity
public class A{
#Id
private long id;
#OneToMany
private List<B> bes;
//boilerplate
}
and I have to sort by bes.size()
Is there a way to somehow customize the ordering still taking the advantage of pagination, filtering and other Spring Data great features?

I've solved the puzzle using hints and inspirations from:
Limiting resultset using #Query anotations by Koitoer
How to order by count() in JPA by MicSim
Exhaustive experiments on my own
The first and most important thing I've not been aware of about spring-data is that even using #Query custom methods one can still create paging queries by simply passing the Pageable object as parameter. This is something that could have been explicitely stated by spring-data documentation as it is definitely not obvious though very powerful feature.
Great, now the second problem - how do I actually sort the results by size of associated collection in JPA? I've managed to come to a following JPQL:
select new package.AwithBCount(count(b.id) as bCount,c) from A a join a.bes b group by a
where AwithBCount is a class that the query results are actually mapped to:
public class AwithBCount{
private Long bCount;
private A a;
public AwithBCount(Long bCount, A a){
this.bCount = bCount;
this.a = a;
}
//getters
}
Excited that I can now simply define my repository like the one below
public interface ARepository extends JpaRepository<A, Long> {
#Query(
value = "select new package.AwithBCount(count(b.id) as bCount,c) from A a join a.bes b group by a",
countQuery = "select count(a) from A a"
)
Page<AwithBCount> findAllWithBCount(Pageable pageable);
}
I hurried to try my solution out. Perfect - the page is returned but when I tried to sort by bCount I got disappointed. It turned out that since this is a ARepository (not AwithBCount repository) spring-data will try to look for a bCount property in A instead of AwithBCount. So finally I ended up with three custom methods:
public interface ARepository extends JpaRepository<A, Long> {
#Query(
value = "select new package.AwithBCount(count(b.id) as bCount,c) from A a join a.bes b group by a",
countQuery = "select count(a) from A a"
)
Page<AwithBCount> findAllWithBCount(Pageable pageable);
#Query(
value = "select new package.AwithBCount(count(b.id) as bCount,c) from A a join a.bes b group by a order by bCount asc",
countQuery = "select count(a) from A a"
)
Page<AwithBCount> findAllWithBCountOrderByCountAsc(Pageable pageable);
#Query(
value = "select new package.AwithBCount(count(b.id) as bCount,c) from A a join a.bes b group by a order by bCount desc",
countQuery = "select count(a) from A a"
)
Page<AwithBCount> findAllWithBCountOrderByCountDesc(Pageable pageable);
}
...and some additional conditional logic on service level (which could be probably encapsulated with an abstract repository implementation). So, although not extremely elegant, that made the trick - this way (having more complex entities) I can sort by other properties, do the filtering and pagination.

One option, which is much simpler than the original solution and which also has additional benefits, is to create a database view of aggregate data and link your Entity to this by means of a #SecondaryTable or #OneToOne.
For example:
create view a_summary_view as
select
a_id as id,
count(*) as b_count,
sum(value) as b_total,
max(some_date) as last_b_date
from b
Using #SecondaryTable
#Entity
#Table
#SecondaryTable(name = "a_summary_view",
pkJoinColumns = {#PrimaryKeyJoinColumn(name = "id", referencedColumnName= "id")})
public class A{
#Column(table = "a_summary_view")
private Integer bCount;
#Column(table = "a_summary_view")
private BigDecimal bTotal;
#Column(table = "a_summary_view")
private Date lastBDate;
}
You can now then sort, filer, query etc purely with reference to entity A.
As an additional advantage you have within your domain model data that may be expensive to compute in-memory e.g. the total value of all orders for a customer without having to load all orders or revert to a separate query.

Thank you #Alan Hay, this solution worked fine for me. I just had to set the foreignKey attribute of the #SecondaryTable annotation and everything worked fine (otherwise Spring Boot tried to add a foreignkey constraint to the id, which raise an error for a sql View).
Result:
#SecondaryTable(name = "product_view",
pkJoinColumns = {#PrimaryKeyJoinColumn(name = "id", referencedColumnName = "id")},
foreignKey = #javax.persistence.ForeignKey(ConstraintMode.NO_CONSTRAINT))

I don't know much about Spring Data but for JPQL, to sort the objects by size of associated collection, you can use the query
Select a from A a order by a.bes.size desc

You can use the name of an attribute found in the select clause as a sort property:
#Query(value = "select a, count(b) as besCount from A a join a.bes b group by a", countQuery = "select count(a) from A a")
Page<Tuple> findAllWithBesCount(Pageable pageable);
You can now sort on property besCount :
findAllWithBesCount(PageRequest.of(1, 10, Sort.Direction.ASC, "besCount"));

I used nativeQuery to arrange sorting by number of records from another table, pagable works.
#Query(value = "SELECT * FROM posts where posts.is_active = 1 and posts.moderation_status = 'ACCEPTED' " +
"group by posts.id order by (SELECT count(post_id) FROM post_comments where post_id = posts.id) desc",
countQuery = "SELECT count(*) FROM posts",
nativeQuery = true)
Page <Post> findPostsWithPagination(Pageable pageable);

For SpringBoot v2.6.6, accepted answer isn't working if you need to use pageable with child's side field especially when using #ManyToOne.
For the accepted answer:
You can return new object with static query method, which have to include order by count(b.id)
And also order by bCount isn't working.
Please use #AlanHay solution, it is working, but you can't use primitive field and change foreign key constraint. For instance, change long with Long. Because:
When saving a new entity Hibernate does think a record has to be written to the secondary table with a value of zero. (if you use primitive type)
Otherwise you will get an exception:
Caused by: org.postgresql.util.PSQLException: ERROR: cannot insert into view "....view"
Here is the example:
#Entity
#Table(name = "...")
#SecondaryTable(name = "a_summary_view,
pkJoinColumns = {#PrimaryKeyJoinColumn(name = "id",
referencedColumnName= "id")},
foreignKey = #javax.persistence.ForeignKey(name = "none"))
public class UserEntity {
#Id
private String id;
#NotEmpty
private String password;
#Column(table = "a_summary_view",
name = "b_count")
private Integer bCount;
}

Hibernate entity with restriction

We have a DB table that is mapped into a hibernate entity. So far everything goes well...
However what we want is to only map enentitys that satisty a specific criteria, like ' distinct(fieldA,fieldB) '...
Is it possible to map with hibernate and hibernate annotations? How can we do it? With #Filter?

I would recommend that you use #Where annotation. This annotation can be used on the element Entity or target entity of a collection. You provide a clause attribute written in sql that will be applied to any select that hibernate performs on that entity. It is very easy to use and very readable.
Here is an example.
#Entity
//I am only interested in Donuts that have NOT been eaten
#Where(clause = "EATEN_YN = 'N'")
public class Donut {
#Column(name = "FILLING")
private String filling;
#Column(name = "GLAZED")
private boolean glazed = true;
#Column(name = "EATEN_YN")
private boolean eaten = false;
...
}

You could create a view and then map that view to entity:
create view my_data as
select ... from ...
#Entity(table="my_data")
public class MyData { ... }
One option is to map the table normally, then you could fetch your always entities through a query or a filter.
You could also make a native SQL query and map the entity on the results:
Query q = sess.createSQLQuery("SELECT DISTINCT fieldA, fieldB FROM some_table")
.addEntity(MyEntity.class);
List<MyEntity> cats = q.list();
It might be also possible to add DISTINCT to this type of HQL query:
select new Family(mother, mate, offspr)
from DomesticCat as mother
join mother.mate as mate
left join mother.kittens as offspr
Methods 1, 3 and 4 will make a read-only mapping.
Could you be more specific about the criteria you are using? The view approach is more generic since you can't do everything with a hibernate query or filter.

perhaps you could create a new Pojo that encapsulates the fields and the condition that they should statisy . And then then make that class a 'custom user defined type', such that Hibernate will have to use the mapping class that you provide, for mapping that 'type'..

In addition to the options mentioned by Juha, you can also create an object directly out of a SQL query using the NamedNativeQuery and SqlResultSetMapping annotations.
#Entity
#SqlResultSetMapping(name = "compositekey", entities =
#EntityResult(entityClass = MiniBar.class,
fields = { #FieldResult(name = "miniBar", column = "BAR_ID"), })
)
#NamedNativeQuery(name = "compositekey",
query = "select BAR_ID from BAR", resultSetMapping = "compositekey")
#Table(name = "BAR")
public class Bar {
Flavor the SQL query to your taste