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JPA CriterialBuilder.concat force to use concat function

I'm using CriteriaBuilder.concat to concatenate 2 Strings, using code below:
Expression<String> concat = criteriaBuilder.concat(expr1, expr2)
But the generated SQL is something like:
select distinct col_1 || col_2
which causes org.hibernate.hql.ast.QuerySyntaxException:
expecting CLOSE, found '||' near line 1, column 48 [
select count(distinct generatedAlias0.hostname || generatedAlias0.device) from ...
^(1,48)
I wonder how to force it to generate the following SQL which uses the concat() function, instead of the || operator?
select distinct concat(col_1, col_2)
Update:
From the error we can see that the problem is more on the Hibernate (v3.6.10.Final) side, which is why making MySQL to accept || for concatenation doesn't help, also updating to a newer version is not an option for me.
Thank you

I've actually found a workaround. by using #Formula (from Hibernate) instead of CriteriaBuilder for the same task, like this:
#Entity
public class MyEntity {
#Column(name="col_a")
private String colA;
#Column(name="col_b")
private String colB;
#Formula("concat(col_a, col_b)")
private String concated;
//...
}
This way I can use the concated field for CriteriaBuilder.countDistinct:
//...
Expression<?> exp = criteriaBuilder.countDistinct(entity.get("concated"));
criteriaQuery.select(exp);
TypedQuery<Long> query = entityManager.createQuery(criteriaQuery);
return query.getSingleResult();
I wish JPA would (or hopefully already) support countDistinct with multiple columns, then all these mess could have been avoided (see: How to countDistinct on multiple columns, the answer was NO).

I had a similar problem with the concat function.
I have used the concat function in a selectCase and this also returns the same QuerySyntaxException.
My workaround is to use the concat function via criteria builder function:
cb().selectCase().when(cb().equal(root.get(Person_.flag), cb().literal("1")),
cb().function("CONCAT", String.class, root.get(Person_.something), cb().literal(" bla bla bla")))
.otherwise(root.get(Person_.something)))
Hibernate Version 4.3.11.Final

I had this issue as well. The JPA/HQL generated sql query use pipes as concat (which is ||).
I am using Mariadb 10, Springboot-data-jpa2.0.6 (with Hibernate 5.2.17)
Issue example
Given HQL: select x from Xxx x where concat(x.field1, x.field2) = $1
Generated SQL: select ..... where (x.field1 || x.field2) = ?
Reason:
Use of || is deprecated, since mysql 8.0, unless the PIPES_AS_CONCAT SQL mode is enabled: https://dev.mysql.com/doc/refman/8.0/en/mysql-nutshell.html
For mariadb: https://mariadb.com/kb/en/or/
Work around:
(preferred) ranther then use concat function, there is a similar one concat_ws: https://mariadb.com/kb/en/concat_ws/
Use JPA native query #Query(nativeQuery = true, value ="select * from ....")
set global sql_mode=<list of modes which contains PIPES_AS_CONCAT>
(I didn't try this)

Hibernate returns list of nulls although executed SQL returns values

I'm using hibernate as an ORMapper. I want to execute an actually rather simple hql query:
SELECT a
FROM Foo a
WHERE a.status = :A0status
ORDER BY a.bookingTypeCode ASC,
a.priority ASC
This hql query is then converted into a sql query which looks something like this:
select a.*
from Foo a
where a.status='A'
order by a.bookingtypecode ASC,
a.priority ASC
When I execute the sql on the oracle database using the Oracle SQL Developer I get 17 rows returned. However, when I execute the hql query (using the list method of a Query I get a list of 17 elements that are all null. Although the number of elements is correct, not a single one of the elements is actually loaded.
This is the way I create and execute my query:
// the hql query is stored in the hqlQuery variable;
// the parameter are stored in a Map<String, Object> called params
Query hQuery = hibSession.createQuery(hqlQuery);
for (Entry<String, Object> param : params.entrySet()) {
String key = param.getKey();
Object value = param.getValue();
hQuery.setParameter(key, value);
}
List<?> result = hQuery.list();
Does anyone know what might be the problem here?
Update 1
I've recently upgrade from hibernate 3.2 to 4.3.5. Before the upgrade everything worked fine. After the upgrade I get this error.

I've set the Log level of hibernate to TRACE and found the problem. It was actually a mapping/logic/database error. The primary key consisted of two columns (according to the entity class) and one of these columns was nullable. However a primary key can never be nullable. Therefore hibernate always returned null.

If you have not set a custom (and buggy) ResultTransformer, my second best guess is that your debugger is lying to you. Does you code actually receives a list of null?
Also make sure to test with the code you are showing is. Too many times, people simplify things and the devil is in the details.

This error is happening to me. MySQL query browser works, but in hibernate of 7 columns and only one column always came with all null fields. I checked all the ids and they were not null. The error was in the construction of SQL Native. I had to change the way of writing it. Ai worked.
SELECT c.idContratoEmprestimo as idContratoEmprestimo,
c.dtOperacao as dataOperacao,
p.cpf as cpf,
p.nome as nome,
(Select count(p2.idParcelaEmprestimo) from EMP_PARCELA p2 where p2.valorPago > 0 and p2.dtPagamento is not null
and p2.idContratoEmprestimo = c.idContratoEmprestimo and p2.mesCompetencia <= '2014-08-01') as parcelasPagas, c.numeroParcelas as numeroParcelas,
pe.valorPago as valorParcela
FROM EMP_CONTRATO c inner join TB_PARTICIPANTE_DADOS_PLANO AS pp on pp.idParticipantePlano = c.idParticipantePlano
inner join TB_PARTICIPANTE as p on p.id = pp.idParticipante
inner join TB_PARTICIPANTE_INSTITUIDOR as pi on pi.PARTICIPANTE_ID = p.id
inner join EMP_PARCELA as pe on pe.idContratoEmprestimo = c.idContratoEmprestimo
where c.dtInicioContrato <= '2014-08-01' and pi.INSTITUIDOR_ID = 1
and c.avaliado is true
and pe.mesCompetencia = '2014-08-01'
and c.deferido is true
and c.dtQuitacao is null
and c.dtExclusao is null
and pe.valorPago is not null
group by c.idContratoEmprestimo
order by p.nome

what is the equelent of sql query in hibernate

In SQL Server i am using this query
select *
from Unit c
ORDER BY CONVERT(INT, LEFT(name, PATINDEX('%[^0-9]%', name + 'z')-1)) desc;
I want this query to use in Hibernate. when I use this in Hibernate I got error
java.lang.IllegalArgumentException: org.hibernate.hql.ast.QuerySyntaxException:unexpected token: LEFT near line 1, column 122
[SELECT c FROM models.entities.UnitEntity c WHERE c.expSetId = :expSetId AND isWaitArea=:isWaitArea ORDER BY CONVERT(INT, LEFT(name, PATINDEX('%[^0-9]%', name + 'z')-1)) asc]

some of that is not in the hibernate dialect, you can change left with substring, convert with cast. and as for patindex i couldn't find the substitution. you either can add pathindex to the constructor of the dialect that you use
registerFunction( "patindex", new StandardSQLFunction("patindex") );
or create patindex() to a stored procedure.
then you can use something like this:
from Unit c order by cast(substring(name, 0, PATINDEX('%[^0-9]%', name + 'z')-1) as integer);
or you can use locate() instead of patindex(), but i think it doesn't support regular expression.

I am pretty sure that you can use SQL query with hibernate as well. When you create your hibernate session, you can use something like
session.createSQLQuery("Your Query Here")
Hope this helps.

executing case expressions in jpql

I'm learning JPA and doing some hands one with JPQL. I am having trouble in CASE expressions.
For example, this query,
Query caseQuery = em
.createQuery("SELECT t , CASE WHEN t.salary = 20000 THEN '20k' WHEN t.salary = 40000 THEN '40k' ELSE 'No salary' END FROM Teacher t");
and executing it using
List<Teacher> teachers = (List<Teacher>) caseQuery.getResultList();
but whenever I try to print the results out, I'm getting ClassCastException that Object cannot be converted to Teacher
I've tried using TypedQuery for Teacher but it didn't work. Could you experts please throw some light on executing this CASE statements in JPQL?

The reason is due to multiple select expressions in your query and not due to CASE Expression ,I believe with multiple select expressions the result will be Object[] rather than translated to the Entity. Some references JPA Tutorial ;JPQL. A related query already in stack overflow.

You should modify
List<Teacher> teachers = (List<Teacher>) caseQuery.getResultList();
to
List<Object[]> teachers = (List<Object[]>) caseQuery.getResultList();
where Object[] will be an array of Teacher& String
For TypedQuery also similar change should work.

How can I use MySQL assign operator(:=) in hibernate native query?

I'm using Hibernate. I wrote some native query because I need to use sub select statement.
Query looks like this:
SELECT sub.rownum FROM
(SELECT k.`news_master_id` AS id, #row := #row + 1 AS rownum
FROM keyword_news_list k
JOIN (SELECT #row := 0) r
WHERE k.`keyword_news_id` = :kid
ORDER BY k.`news_master_id` ASC) AS sub
WHERE sub.id = :nid
When I run this query like this:
sessionFactory.getCurrentSession()
.createSQLQuery(query)
.setParameter("kid", kid)
.setParameter("nid", nid)
.uniqueResult();
This exception comes out:
org.hibernate.QueryException: Space is not allowed after parameter prefix ':' ....
This might because of := operator. I found some Hibernate issue about this. This issue is still open. Isn't there any solution for this problem?

Note that HHH-2697 is now fixed for Hibernate 4.1.3 You can now escape with backslash:
SELECT k.`news_master_id` AS id, #row \:= #row + 1 AS rownum
FROM keyword_news_list k
JOIN (SELECT #row \:= 0) r
WHERE k.`keyword_news_id` = :kid
ORDER BY k.`news_master_id` ASC

Another solution for those of us who can't make the jump to Hibernate 4.1.3.
Simply use /*'*/:=/*'*/ inside the query. Hibernate code treats everything between ' as a string (ignores it). MySQL on the other hand will ignore everything inside a blockquote and will evaluate the whole expression to an assignement operator.
I know it's quick and dirty, but it get's the job done without stored procedures, interceptors etc.

you can implement this is a slightly different way.. you need to replace the : operator with something else (say '|' char ) and in your interceptor replace the '|' with the : .
this way hibernate will not try to think the : is a param but will ignore it
For the interceptor logic you can refer to the hibernate manual
This has worked for me using MySQL 5.
remember, this replacing of : must be only done to ':=' and other MySQL specific requirments.. don't try to replace the : for the param-placeholders. (hibernate will not be able to identify the params then)

I prefer to include Spring JDBC and execute the query rather than fight against Hibernate interceptors.

in Hibernate exception on encountering mysql := operator Stanislav gave another option other than interceptor to solve this issue

If you keep your SQL-files away from Java code - try this piece of code. Played a lot to get the right number of escaping slashes:
String sqlPattern = FileUtils.readFile(this.getClass(), /sql/my_query.sql");
sqlPattern = sqlPattern.replaceAll(":=", "\\\\:=");
Query query = entityManager.createNativeQuery(sqlPattern);

I guess there should not be a space after = , the operator should be written as =: (without any spaces)