I have some specifications that I am combining with "and":
Specification.where(predicate1).and(predicate2).and(predicate3);
One of them has distinct set :
query.distinct(true);
Another one makes an order by on a column that is in a join.
query.orderBy(builder.desc(bJoin.get("orderbyColumn")));
This fails with a SQLGrammarException stating that order by column should be in distinct.
So basically we have entity A, the main entity, and some nested entity B, we select from A but want to order by B, and in generated sql it only selects columns from A. The only way I found to make it work (= making it select from B as well) is to replace the join by a fetch :
Fetch < A, B > bFetch = root.fetch("joinCol", JoinType.INNER);
Join < A, B > bJoin = (Join < A, B > ) bFetch;
that worked for some time, was testing locally in H2, but then after some time started getting another error :
org.hibernate.QueryException: query specified join fetching, but the
owner of the fetched association was not present in the select list
I solved it somehow in my local pointing to H2 by requiring some columns to not be null, but in real server using PostgreSQL, it's not working at all, getting that error for all cases when a fetch is present.
My question is : what is the right way to use distinct along with orderby on a nested entity that is not fetched? Is my solution with fetch ok and it just needs to be fixed (and if so how?) or I should go for another option entirely?
For the actual query I am using this method :
findAll(Specification<>, Pageable)
Isn't there a way to have distinct wrapping the whole query with order by (some sort of subquery?) and bypassing all this nightmare? Have it generate a query like this:
select distinct colA1, colA2, coAl3 from (select colA1, colA2, coAl3
from A inner join B b on ........ order by b.colB1)
Do I need to convert my specification to predicate manually and do something else with it to try to solve my issues (some kind of hybrid approach)?
Any pieces of advice will be greatly appreciated.
I encountered same error but actually it was not error :)
findAll(Specification<>, Pageable) this method throws 2 different queries.
First one is count query where you have to be careful.
Second is the rows query where you actually did it.
You can check the query type with code below
if (query.getResultType() != Long.class && query.getResultType() != long.class){
root.fetch("entity1");
}
Related
In my webapp I need to create a query engine module where the user selects in the view what columns and filters he want and get the datas related to these queries.
So, I have to build SQL dynamic queries with this kind of format :
SELECT {columns} FROM MainTable FULL OUTER JOIN SecondTable ON ... FULL OUTER JOIN ThirdTable ON ... WHERE {filters}
The columns and filters are known at runtime. (read-only)
Actually, I have a big SQL Server view (Mapped entity in Java) which make 3 FULL OUTER JOIN of others SQL server views. And I build the query in the source code by parsing keywords as AND, OR, number, date, text, ...
Finally, I return a response in the front-end module a table with datas.
But, I'm facing performance issues (scalability) with this method and I'm looking for a more efficient way to do that.
Is it possible to split the SELECT query mentionned above in subqueries to improve performances ? Or there is better design approach for that ?
Here the request I actually use (names changed) with Hibernate :
SELECT * FROM BigView "+WHERE+" OPTION(ROBUST PLAN)
(BigView is aggregation of 4 views : RootTable, Table2, Table3, Table4)
Btw, I know "+WHERE+" is a bad practice but this is not the concern of this topic
I thought using this instead (delete BigView in SQL Server and the related entity) but it actually does same thing even if there is a little performance gain with the columns restriction :
SELECT ROW_NUMBER() OVER (ORDER BY id) AS rownum, tmp.* FROM ( SELECT '' AS id, "+columns+" "+
"FROM RootTable FULL OUTER JOIN "+
"Table2 ON RootTable.RT_ID = Table2.RT_N FULL OUTER JOIN "+
"Table3 ON RootTable.RT_ID = Table3.RT_ID FULL OUTER JOIN "+
"Table4 ON RootTable.RT_ID = Table4.RT_N "+
WHERE+" ) AS tmp
My previous deleted question was not enough focused so I hope this one is correct.
EDIT : I add this filter (WHERE clause) to show what can be requested for example :
RT_ID>'10' AND ( Table2_Topic LIKE '%test%' OR Table3_Date=CONVERT(datetime, '24/09/2020', 103) OR ( Table3_N is not null and Table2_ID<>0 ) )
I've a class Lawsuit, that contains a List<Hearing>, each one with a Date attribute.
I need to select all the Lawsuits ordered by the date of their Hearings
I've a CriteriaQuery like
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Lawsuit> cq = cb.createQuery(Lawsuit.class);
Root<Lawsuit> root = cq.from(Lawsuit.class);
I use distinct to flatten the results:
cq.select(root).distinct(true);
I then join Lawsuit with Hearing
Join<Lawsuit, Hearing> hearing = root.join("hearings", JoinType.INNER);
to create Predicates
predicateList.add(cb.isNotNull(hearing.<Date>get("date")));
and Orders:
orderList.add(cb.asc(hearing.<Date>get("date")));
Everything works fine if I avoid distinct, but if I use it, it complains about not being able to order based on fields that are not in the SELECT:
Caused by: org.postgresql.util.PSQLException: ERROR: for SELECT DISTINCT, ORDER BY expressions must appear in select list
The List<Hearing> is already accessible through the Lawsuit classes returned, so I'm confused: how should I add them to the select list ?
I've discovered the source of the problem somewhere else, and solving it has made unnecessary to do what asked in the question;
as described in other answers, it should be unnecessary to perform the distinct here.
The duplicate rows were originated by erroneous left joins that were performed on collections (attributes of the root object) even if the predicates were not been used:
Join<Lawsuit, Witness> witnesses = root.join("witnesses", JoinType.LEFT);
if (witnessToFilterWith!=null) {
predicateList.add(cb.equal(witnesses.<Long>get("id"),witnessToFilterWith.getId()));
}
The join should obviously be performed as inner and only if needed:
if (witnessToFilterWith!=null) {
Join<Lawsuit, Witness> witnesses = root.join("witnesses", JoinType.INNER);
predicateList.add(cb.equal(witnesses.<Long>get("id"),witnessToFilterWith.getId()));
}
So, if you're here because you're getting the same problem, search the problem in the joins.
You can also de-duplicate via group by based on primary key column of root table:
cq.groupBy(root.get("id")); // Assuming that Lawsuite.id is primary key column
What alternatives do I have to implement a union query using hibernate? I know hibernate does not support union queries at the moment, right now the only way I see to make a union is to use a view table.
The other option is to use plain jdbc, but this way I would loose all my example/criteria queries goodies, as well as the hibernate mapping validation that hibernate performs against the tables/columns.
You could use id in (select id from ...) or id in (select id from ...)
e.g. instead of non-working
from Person p where p.name="Joe"
union
from Person p join p.children c where c.name="Joe"
you could do
from Person p
where p.id in (select p1.id from Person p1 where p1.name="Joe")
or p.id in (select p2.id from Person p2 join p2.children c where c.name="Joe");
At least using MySQL, you will run into performance problems with it later, though. It's sometimes easier to do a poor man's join on two queries instead:
// use set for uniqueness
Set<Person> people = new HashSet<Person>((List<Person>) query1.list());
people.addAll((List<Person>) query2.list());
return new ArrayList<Person>(people);
It's often better to do two simple queries than one complex one.
EDIT:
to give an example, here is the EXPLAIN output of the resulting MySQL query from the subselect solution:
mysql> explain
select p.* from PERSON p
where p.id in (select p1.id from PERSON p1 where p1.name = "Joe")
or p.id in (select p2.id from PERSON p2
join CHILDREN c on p2.id = c.parent where c.name="Joe") \G
*************************** 1. row ***************************
id: 1
select_type: PRIMARY
table: a
type: ALL
possible_keys: NULL
key: NULL
key_len: NULL
ref: NULL
rows: 247554
Extra: Using where
*************************** 2. row ***************************
id: 3
select_type: DEPENDENT SUBQUERY
table: NULL
type: NULL
possible_keys: NULL
key: NULL
key_len: NULL
ref: NULL
rows: NULL
Extra: Impossible WHERE noticed after reading const tables
*************************** 3. row ***************************
id: 2
select_type: DEPENDENT SUBQUERY
table: a1
type: unique_subquery
possible_keys: PRIMARY,name,sortname
key: PRIMARY
key_len: 4
ref: func
rows: 1
Extra: Using where
3 rows in set (0.00 sec)
Most importantly, 1. row doesn't use any index and considers 200k+ rows. Bad! Execution of this query took 0.7s wheres both subqueries are in the milliseconds.
Use VIEW. The same classes can be mapped to different tables/views using entity name, so you won't even have much of a duplication. Being there, done that, works OK.
Plain JDBC has another hidden problem: it's unaware of Hibernate session cache, so if something got cached till the end of the transaction and not flushed from Hibernate session, JDBC query won't find it. Could be very puzzling sometimes.
I have to agree with Vladimir. I too looked into using UNION in HQL and couldn't find a way around it. The odd thing was that I could find (in the Hibernate FAQ) that UNION is unsupported, bug reports pertaining to UNION marked 'fixed', newsgroups of people saying that the statements would be truncated at UNION, and other newsgroups of people reporting it works fine...
After a day of mucking with it, I ended up porting my HQL back to plain SQL, but doing it in a View in the database would be a good option. In my case, parts of the query were dynamically generated, so I had to build the SQL in the code instead.
I have a solution for one critical scenario (for which I struggled a lot )with union in HQL .
e.g. Instead of not working :-
select i , j from A a , (select i , j from B union select i , j from C) d where a.i = d.i
OR
select i , j from A a JOIN (select i , j from B union select i , j from C) d on a.i = d.i
YOU could do in Hibernate HQL ->
Query q1 =session.createQuery(select i , j from A a JOIN B b on a.i = b.i)
List l1 = q1.list();
Query q2 = session.createQuery(select i , j from A a JOIN C b on a.i = b.i)
List l2 = q2.list();
then u can add both list ->
l1.addAll(l2);
A view is a better approach but since hql typically returns a List or Set... you can do list_1.addAll(list_2). Totally sucks compared to a union but should work.
Perhaps I had a more straight-forward problem to solve. My 'for instance' was in JPA with Hibernate as the JPA provider.
I split the three selects (two in a second case) into multiple select and combined the collections returned myself, effectively replacing a 'union all'.
Hibernate 6 added support for UNION.
So, you can now use UNION in JPQL queries like this:
List<String> topics = entityManager.createQuery("""
select c.name as name
from Category c
union
select t.name as name
from Tag t
""", String.class)
.getResultList();
And you can also also use UNION ALL if there are no duplicates to be removed:
List<String> topics = entityManager.createQuery("""
select c.name as name
from Category c
union all
select t.name as name
from Tag t
""", String.class)
.getResultList();
Besides UNION, you can also use EXCEPT and INTERSECT.
I too have been through this pain - if the query is dynamically generated (e.g. Hibernate Criteria) then I couldn't find a practical way to do it.
The good news for me was that I was only investigating union to solve a performance problem when using an 'or' in an Oracle database.
The solution Patrick posted (combining the results programmatically using a set) while ugly (especially since I wanted to do results paging as well) was adequate for me.
Here is a special case, but might inspire you to create your own work around. The goal here is to count the total number of records from two different tables where records meet a particular criteria. I believe this technique will work for any case where you need to aggregate data from across multiple tables/sources.
I have some special intermediate classes setup, so the code which calls the named query is short and sweet, but you can use whatever method you normally use in conjunction with named queries to execute your query.
QueryParms parms=new QueryParms();
parms.put("PROCDATE",PROCDATE);
Long pixelAll = ((SourceCount)Fetch.row("PIXEL_ALL",parms,logger)).getCOUNT();
As you can see here, the named query begins to look an aweful lot like a union statement:
#Entity
#NamedQueries({
#NamedQuery(
name ="PIXEL_ALL",
query = "" +
" SELECT new SourceCount(" +
" (select count(a) from PIXEL_LOG_CURR1 a " +
" where to_char(a.TIMESTAMP, 'YYYYMMDD') = :PROCDATE " +
" )," +
" (select count(b) from PIXEL_LOG_CURR2 b" +
" where to_char(b.TIMESTAMP, 'YYYYMMDD') = :PROCDATE " +
" )" +
") from Dual1" +
""
)
})
public class SourceCount {
#Id
private Long COUNT;
public SourceCount(Long COUNT1, Long COUNT2) {
this.COUNT = COUNT1+COUNT2;
}
public Long getCOUNT() {
return COUNT;
}
public void setCOUNT(Long COUNT) {
this.COUNT = COUNT;
}
}
Part of the magic here is to create a dummy table and insert one record into it. In my case, I named it dual1 because my database is Oracle, but I don't think it matters what you call the dummy table.
#Entity
#Table(name="DUAL1")
public class Dual1 {
#Id
Long ID;
}
Don't forget to insert your dummy record:
SQL> insert into dual1 values (1);
As Patrick said, appending the LISTs from each SELECT would be a good idea but remember that it acts like UNION ALL. To avoid this side effect, just control if the object is already added in final collection or not. If no, then add it.
Something else that you should care about is that if you have any JOIN in each SELECT, the result would be a list of object array(List<Object[]>) so you have to iterate over it to only keep the object that you need.
Hope it works.
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
I'm new to ORM stuff and I need some help understanding something.
Let's assume I have the following standard SQL query:
SELECT *, COUNT(test.testId) AS noTests FROM inspection
LEFT JOIN test ON inspection.inspId = test.inspId
GROUP BY inspection.inspId
which I want to use in JPA.
I have an Inspection entity with a one-to-many relationship to a Test entity. (an inspection has many tests)
I tried writing this in JPQL:
Query query = em.createQuery("SELECT insp, COUNT(???what???) " +
"FROM Inspection insp LEFT JOIN insp.testList " +
"GROUP BY insp.inspId");
1) How do I write the COUNT clause? I'd have to apply count to elements from the test table but testList is a collection, so I can't do smth like COUNT(insp.testList.testId)
2) Assuming 1 is resolved, what type of object will be returned. It will definitely not be an Inspection object... How do I use the result?
You can give an alias to the joined entity (with AS)
You can create either a new object, or a List with the returned values
So:
SELECT new com.yourproject.ResultHolder(insp, COUNT(test.testId))
FROM Inspection insp LEFT JOIN insp.testList AS test GROUP BY insp.inspId
Or
SELECT new list(insp, COUNT(test.testId))
FROM Inspection insp LEFT JOIN insp.testList AS test GROUP BY insp.inspId
The result is then accessible either as an instance of ResultHolder, or as a java.util.List, where the insp is list.get(0), and the count is list.get(1)