Develop Reference

GREATER / LEAST functions in QueryDSL [duplicate]

I am have a problem where i need to join two tables using the LEAST and GREATEST functions, but using JPA CriteriaQuery. Here is the SQL that i am trying to duplicate...
select * from TABLE_A a
inner join TABLE_X x on
(
a.COL_1 = least(x.COL_Y, x.COL_Z)
and
a.COL_2 = greatest(x.COL_Y, x.COL_Z)
);
I have looked at CriteriaBuilder.least(..) and greatest(..), but am having a difficult time trying to understand how to create the Expression<T> to pass to either function.

The simplest way to compare two columns and get the least/greatest value is to use the CASE statement.
In JPQL, the query would look like
select a from EntityA a join a.entityXList x
where a.numValueA=CASE WHEN x.numValueY <= x.numValueZ THEN x.numValueY ELSE x.numValueZ END
and a.numValueB=CASE WHEN x.numValueY >= x.numValueZ THEN x.numValueY ELSE x.numValueZ END
You can code the equivalent using CriteriaBuilder.selectCase() but I've never been a big fan of CriteriaBuilder. If requirements forces you to use CriteriaBuilder then please let me know and I can try to code the equivalent.
CriteriaBuilder least/greatest is meant to get the min/max value of all the entries in one column. Let's say you want to get the Entity that had the alphabetically greatest String name. The code would look like
CriteriaBuilder cb = entityManager.getCriteriaBuilder();
CriteriaQuery query = cb.createQuery(EntityX.class);
Root<EntityX> root = query.from(EntityX.class);
Subquery<String> maxSubQuery = query.subquery(String.class);
Root<EntityX> fromEntityX = maxSubQuery.from(EntityX.class);
maxSubQuery.select(cb.greatest(fromEntityX.get(EntityX_.nameX)));
query.where(cb.equal(root.get(EntityX_.nameX), maxSubQuery));
I created a sample Spring Data JPA app that demonstrates these JPA examples at
https://github.com/juttayaya/stackoverflow/tree/master/JpaQueryTest

It turns out that CriteriaBuilder does support calling LEAST and GREATEST as non-aggregate functions, and can be accessed by using the CriteriaBuilder.function(..), as shown here:
Predicate greatestPred = cb.equal(pathA.get(TableA_.col2),
cb.function("greatest", String.class,
pathX.get(TableX_.colY), pathX.get(TableX_.colZ)));

Criteria API Ordering by nested aggregated property

How do I implement ordering objects by aggregated nested property?
I have Photographer entity which one has a lot of PhotographerPrice entities (One to Many) with BigDecimal property called pricePerHour. When I retrieving photographers I want to sort them by the minimal price of whole prices they have.
CriteriaBuilder cb = entityManager.getCriteriaBuilder();
CriteriaQuery<Photographer> cq = cb.createQuery(Photographer.class);
Root<Photographer> root = cq.from(Photographer.class);
List<Predicate> predicates = new ArrayList<>(); // I have a lot of predicates which set if data was present by client
I tried to make a subquery to PhotographerPrice and than sort in root
Subquery<BigDecimal> subquery = cq.subquery(BigDecimal.class);
Root<PhotographerPrice> from = subquery.from(PhotographerPrice.class);
Predicate and = cb.and(
cb.equal(root.get(Photographer_.id), from.get(PhotographerPrice_.photographer).get(Photographer_.id)),
cb.isNotNull(from.get(PhotographerPrice_.pricePerHour))
);
subquery.correlate(root);
subquery.where(and);
subquery.select(cb.min(from.get(PhotographerPrice_.pricePerHour)));
subquery.groupBy(from.get(PhotographerPrice_.photographer).get(Photographer_.id));
...
cq.orderBy(cb.asc(subquery));
But, as I realized, it's not allowed to use a subquery in order by clause.
So, how do I can implement something like this using Criteria API:
select *
from photographer p
order by (
select min(price_per_hour) minPrice
from photographer_price pp
where p.id = pp.photographer_id
and pp.photo_per_hour is not null
group by photographer_id
);
When I tried to implement it with Join approach I've got duplicates in my result list.
Is it possible to implement it using Criteria API? Maybe there is another tool to make filtering for entities from DB more convenient? I have a lot of different parameters for filtering and sorting which related to nested properties, sometimes even related to nested in a nested property.
The only way I found to solve it:
ListJoin<Photographer, PhotographerPrice> join = root.join(Photographer_.photographerPrices);
Expression<BigDecimal> min = cb.min(join.get(PhotographerPrice_.pricePerHour));
cq.orderBy(cb.desc(min));
cq.groupBy(root.get(Photographer_.id));
But I don't sure about group by. Is it possible some troubleshooting appear later?

The approach I found that works in my case
Do left join to PhotographerPrice with Min aggregate function after that make an order based by result of this aggregate:
ListJoin<Photographer, PhotographerPrice> photographerPriceJoin = root.join(Photographer_.photographerPrices);
Expression<BigDecimal> min = cb.min(photographerPriceJoin.get(PhotographerPrice_.pricePerHour));
if (photographerCatalogFilter.getDirection().isDescending()) {
orderList.add(cb.desc(min));
} else {
orderList.add(cb.asc(min));
}

how to use "or" operator with CriteriaQuery in spring-data-elasticsearch

Recently, I am trying use spring-data-elasticsearch in my project and met lots of problems. I asked a question about not operation yesterday but I solved by myself. And now I met another problem when trying to use or operator.
Here is what I want:
I want to query an object with a code that is not "11" and its symbol is "22" or its subSymbol is "33". I have tried many times in many ways and failed.It seems that I have no way to make it work with CriteriaQuery. I don't know if I described my question clearly. And in SQL, it should be written like this,
select from x where x.code!='11' and (x.symbol='22' or x.subSymbol='33')
But with CriteriaQuery, I always get the results if symbol/subSymbol value is matched and code condition seems missing, its SQL works like below:
select from x where x.code!='11' or x.symbol='22' or x.subSymbol='33'
Here is what I tried:
1.
CriteriaQuery criteriaQuery = new CriteriaQuery(new Criteria()
.and("code").is("11").not()
.or("symbol").is("22").or("subSymbol").is("33"));
2.
CriteriaQuery criteriaQuery = new CriteriaQuery(new Criteria()
.and("code").is("11").not()
.or(new Criteria("symbol").is("22").and("subSymbol").is("33")));
3.
CriteriaQuery criteriaQuery = new CriteriaQuery(new Criteria()
.and("code").is("11").not()
.and(new Criteria("symbol").is("22").or("subSymbol").is("33")));
4.
CriteriaQuery criteriaQuery = new CriteriaQuery(new Criteria()
.and("code").is("11").not())
.addCriteria(new Criteria("symbol").is("22").or("subSymbol").is("33"));
List<xx> sampleEntities =
elasticsearchTemplate.queryForList(criteriaQuery,xx.class);
All of the above failed.
So any solution to deal with my problem? Or I need to try NativeSearchQueryBuilder maybe? It is so frustrating.

I think you need to index your properties as Terms, because you use them as some codes(nomenclatures). You can keep the existing indexing as text if you need it in future. So I found this tutorial which looks easy to implement for your case.
https://www.baeldung.com/spring-data-elasticsearch-queries
So if you add #InnerField on your fields and use query 2. but use verbatim suffix on fields it should work with query number 2 from your list. Your fields will be like code.verbatim, etc...
Also you can think of moving to NativeSearchQueryBuilder.

Why is this Java query failing? returning 0 when there are results

Hi can anyone tell me why this java query is failing?
Query q = entityManager.createNativeQuery("SELECT m.* FROM MdmAudit m WHERE m.correlationID = :correlationId AND m.verb = :verb", MdmAuditDAO.class);
//Query q = entityManager.createNamedQuery("MdmAuditDAO.GetData");
q.setParameter("correlationId", resp.getHeader().getCorrelationID());
q.setParameter("verb", resp.getHeader().getVerb());
long result = (long) q.getFirstResult();
The namedQuery:
#NamedQuery( name="MdmAuditDAO.GetData", query="SELECT m FROM MdmAuditDAO m WHERE m.correlationId = :correlationId AND m.verb = :verb")
public class MdmAuditDAO implements Serializable {
I have getters and setter in my MdmAuditDAO class, and I have checked the naming of the variables, and they are identical as in the NamedQuery, so the problem does not lie there.
My problem is that I have three entries in my database, I should at least get one answer back but I get 0 in my result.
MdmAuditDAO is defined in my persistence.xml and in my ehcache.xml. So why is it that the result I get returned is 0? I have also tried to get an object returned or a list of objects, and it is the same result, nothing gets returned, but when I run my query in my mssql database I get results see picture below. It has nothing to do with the m.* I aslo get results when I use that in my SELECT statement.
EDIT 1: This is what I get from my hibernate log, and I do not know how to read this?
Hibernate:
select
mdmauditda0_.id as id1_7_,
mdmauditda0_.correlationID as correlat2_7_,
mdmauditda0_.messageID as messageI3_7_,
mdmauditda0_.meter_no as meter_no4_7_,
mdmauditda0_.noun as noun5_7_,
mdmauditda0_.payload as payload6_7_,
mdmauditda0_.source as source7_7_,
mdmauditda0_.subtype as subtype8_7_,
mdmauditda0_.time as time9_7_,
mdmauditda0_.verb as verb10_7_
from
MdmAudit mdmauditda0_
where
mdmauditda0_.correlationID=?
Anything I have to set, to get more information? I am using the following jars
And my java version is 1.7.0_79.

I found the solution http://www.objectdb.com/api/java/jpa/Query/getFirstResult returns the position of the first element, but I was a bit confused by the phrase
Returns 0 if setFirstResult was not applied to the query object.
Could not get my head around it to make any sense of it.
My solution now is that I just return a list of objects
Query q = entityManager.createNativeQuery("SELECT m.* FROM MdmAudit m WHERE m.correlationId = :correlationId AND verb = :verb", MdmAuditDAO.class);
//Query q = entityManager.createNamedQuery("MdmAuditDAO.GetData");
q.setParameter("correlationId", resp.getHeader().getCorrelationID());
q.setParameter("verb", resp.getHeader().getVerb());
List<MdmAuditDAO> mdmAuditList = q.getResultList();
And then it works fine and I get results. So instead of the the result == 0 check I am doing later in my code I just do a NULL and isEmpty() check instead().
Side note: I have not tried to delete entries and then see what the result would be then in the q.getFirstResult() call but that would be a possibility and see what i get returned and then check on that value, properbly null?

Loading multiple entities by id efficiently in Hibernate

So, I'm getting a number of instances of a particular entity by id:
for(Integer songId:songGroup.getSongIds()) {
session = HibernateUtil.getSession();
Song song = (Song) session.get(Song.class,id);
processSong(song);
}
This generates a SQL query for each id, so it occurred to me that I should do this in one, but I couldn't find a way to get multiple entities in one call except by running a query. So I wrote a query
return (List) session.createCriteria(Song.class)
.add(Restrictions.in("id",ids)).list();
But, if I enable 2nd level caching doesn't that mean that my old method would be able to return the objects from the 2nd level cache (if they had been requested before) but my query would always go to the database.
What the correct way to do this?

What you're asking to do here is for Hibernate to do special case handling for your Criteria, which is kind of a lot to ask.
You'll have to do it yourself, but it's not hard. Using SessionFactory.getCache(), you can get a reference to the actual storage for cached objects. Do something like the following:
for (Long id : allRequiredIds) {
if (!sessionFactory.getCache().containsEntity(Song.class, id)) {
idsToQueryDatabaseFor.add(id)
} else {
songs.add(session.get(Song.class, id));
}
}
List<Song> fetchedSongs = session.createCriteria(Song.class).add(Restrictions.in("id",idsToQueryDatabaseFor).list();
songs.addAll(fetchedSongs);
Then the Songs from the cache get retrieved from there, and the ones that are not get pulled with a single select.

If you know that the IDs exist, you can use load(..) to create a proxy without actually hitting the DB:
Return the persistent instance of the given entity class with the given identifier, obtaining the specified lock mode, assuming the instance exists.
List<Song> list = new ArrayList<>(ids.size());
for (Integer id : ids)
list.add(session.load(Song.class, id, LockOptions.NONE));
Once you access a non-identifier accessor, Hibernate will check the caches and fallback to DB if needed, using batch-fetching if configured.
If the ID doesn't exists, a ObjectNotFoundException will occur once the object is loaded. This might be somewhere in your code where you wouldn't really expect an exception - you're using a simple accessor in the end. So either be 100% sure the ID exists or at least force a ObjectNotFoundException early where you'd expect it, e.g. right after populating the list.

There is a difference between hibernate 2nd level cache to hibernate query cache.
The following link explains it really well: http://www.javalobby.org/java/forums/t48846.html
In a nutshell,
If you are using the same query many times with the same parameters then you can reduce database hits using a combination of both.

Another thing that you could do is to sort the list of ids, and identify subsequences of consecutive ids and then query each of those subsequences in a single query. For example, given List<Long> ids, do the following (assuming that you have a Pair class in Java):
List<Pair> pairs=new LinkedList<Pair>();
List<Object> results=new LinkedList<Object>();
Collections.sort(ids);
Iterator<Long> it=ids.iterator();
Long previous=-1L;
Long sequence_start=-1L;
while (it.hasNext()){
Long next=it.next();
if (next>previous+1) {
pairs.add(new Pair(sequence_start, previous));
sequence_start=next;
}
previous=next;
}
pairs.add(new Pair(sequence_start, previous));
for (Pair pair : pairs){
Query query=session.createQuery("from Person p where p.id>=:start_id and p.id<=:end_id");
query.setLong("start_id", pair.getStart());
query.setLong("end_id", pair.getEnd());
results.addAll((List<Object>)query.list());
}

Fetching each entity one by one in a loop can lead to N+1 query issues.
Therefore, it's much more efficient to fetch all entities at once and do the processing afterward.
Now, in your proposed solution, you were using the legacy Hibernate Criteria, but since it's been deprecated since Hibernate 4 and will probably be removed in Hibernate 6, so it's better to use one of the following alternatives.
JPQL
You can use a JPQL query like the following one:
List<Song> songs = entityManager
.createQuery(
"select s " +
"from Song s " +
"where s.id in (:ids)", Song.class)
.setParameter("ids", songGroup.getSongIds())
.getResultList();
Criteria API
If you want to build the query dynamically, then you can use a Criteria API query:
CriteriaBuilder builder = entityManager.getCriteriaBuilder();
CriteriaQuery<Song> query = builder.createQuery(Song.class);
ParameterExpression<List> ids = builder.parameter(List.class);
Root<Song> root = query
.from(Song.class);
query
.where(
root.get("id").in(
ids
)
);
List<Song> songs = entityManager
.createQuery(query)
.setParameter(ids, songGroup.getSongIds())
.getResultList();
Hibernate-specific multiLoad
List<Song> songs = entityManager
.unwrap(Session.class)
.byMultipleIds(Song.class)
.multiLoad(songGroup.getSongIds());
Now, the JPQL and Criteria API can benefit from the hibernate.query.in_clause_parameter_padding optimization as well, which allows you to increase the SQL statement caching mechanism.
For more details about loading multiple entities by their identifier, check out this article.