I have following as table structure
**BPV table**
id, vid, bid
**vt table**
vid, name, gender
**uv table**
uvid, vid, cast,...
i want to write left join between BPV ,uv based on vid in hibernate (mysql)
bpv entity have vt as one to one as well as uv have vt with one to one but there is no bpv &uv in realation
Hibernate has Criteria API, which is a good way to execute queries in a OO approach. If you have your persistent entities, then you can do this:
Criteria criteria = session.createCriteria(BPV.class, "bpv");
criteria.createCriteria("bpv.vt", "vt", CriteriaSpecification.LEFT_JOIN);
criteria.createCriteria("vt.uv", "uv", CriteriaSpecification.LEFT_JOIN);
// add restrictions
return criteria.list();
Hibernate SQL:
from BPV where BPV.uv.cast = "your_condition"
It requires properly described entities and dependency;
or pure SQL:
select * from BPV left join uv on BPV.vid = uv.vid where uv.cast = "your_condition"
What you're asking for is not posible, there is a Theta Join solution but it only supports inner join, so you have to give up on that approach and do one of the following solutions:
Map the proper relationship:
If this query is a unusual escenario, you dont necesary have to change your actual mapping , you can make a new dto Class with the new mapping, and use that one for this query.
Use native SQL:
This is prettly simple too, use .createSQLQuery(), to run the native query and you can use .addScalar() + .setResultTransformer(Transformers.aliasToBean(someDto.class)) to get a list of your entity.
Related
I have been trying to get Hibernate to generate me a query with a subquery in its where clause. I've used this answer as a base to help me going, but this question mentioned only one table.
However, this is what I would need (in SQL):
SELECT [...]
FROM a
LEFT OUTER JOIN b on a.idb = b.idb
LEFT OUTER JOIN c on b.idc = c.idc
[...]
LEFT OUTER JOIN k out on j.idk = k.idk
WHERE k.date = (SELECT max(date) from k in where in.idk = out.idk) OR k.date is null
As I am not very used to using Hibernate, I'm having trouble specifying these inner joins while navigating in the inner constraints.
I was able to re-create the initial criteria as in the linked answer, but I can't seem to join the criteria and the rootCriteria.
If the entities are properly joined with #ManyToOne annotations, simply joining the criteria to the previous table will be enough to propagate the criteria to the whole query.
The following code seems to work properly to add the WHERE clause I'm looking for.
DetachedCriteria kSubquery = DetachedCriteria.forClass(TableJPE.class,"j2");
kSubQuery = kSubQuery.createAlias("k","k2");
kSubQuery.setProjection(Projections.max("k2.date"));
kSubQuery = kSubQuery.add(Restrictions.eqProperty("j.id", "j2.id"));
rootCriteria.add(Restrictions.disjunction()
.add(Subqueries.propertyEq("k.date",kSubQuery))
.add(Restrictions.isNull("k.date")));
Context
I send some files to some enterprises every week. I need to restitute for each week and each enterprise whether the file is sent or not.
Tables
ent (enterprise)
wek (week)
fil (file : references wek and ent)
Solution with pure SQL
Make a cartesian product between ent and wek then left outer join fil. This works :
select * from
(
select * from wek, ent e
) as t1
left join fil f
on f.ent_id = t1.ent_id
and f.wek_id = t1.wek_id
Problem :
How to translate this into JPA (in the CriteriaBuilder way)?
For example, if I try :
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<ResultClass> query = cb.createQuery(ResultClass.class);
Root<Week> week = query.from(Week.class);
Root<Enterprise> query.from(Enterprise.class);
Expression<???> cartesianProduct = ??? //How?
cartesianProduct.leftJoin(???_.file);
query.where(
cb.equal(file.get(File_.wek_id), week.get(Week.week_id));
)
Using 2 "from" clauses gives me the cartesian product but how do I left join this result?
Unstatisfaying solution :
Create a view :
CREATE VIEW view_ent_wek AS
SELECT ent_id as ent_id, wek_id as wek_id, ent_id || '-' || ent_id as id
FROM ent, wek;
Map it to an entity :
#Entity
#Table(name = "view_ent_wek")
public class WeekEnterprise {
#Id
#Column(name = "id")
private String id;
#ManyToOne
#JoinColumn(name = "ent_id")
private Enterprise enterprise;
#ManyToOne
#JoinColumn(name = "wek_id")
private Week week;
[...]
Then I can use it in a query :
Root<WeekEnterprise> weekEnterprise = query.from(WeekEnterprise.class);
weekEnterprise.join(...)
I don't like this solution because it makes me create a view that is obviously not necessary. Any idea?
I don't see the point of doing the reporting-style SQL query with JPA, let alone with Criteria Query.
Of course, JPA (and its implementations) do support tuple queries (as opposed to entity queries, see also: Hibernate tuple criteria queries), but tuple queries is not what JPA is good at. Imagine you want to change that report and add more calculations. Wouldn't it be much easier to do that with SQL?
Using JPA for mapping to Java objects and for transaction modelling still makes sense, and thus, your SQL view solution is already quite good, or if you prefer not to store the SQL in a view, use JPA's native query API:
List<Object[]> list = em.createNativeQuery(sql).getResultList();
Or:
List<WeekEnterprise> list = em.createNativeQuery(sql, WeekEnterprise.class)
.getResultList();
I have some ideas:
With 2 JPA queries. First: fetch the cartesian product of wek and enterprises. Second: take an inner join between wek, enterprises and files. Uses a map (wek_id+ent_id => Tuple(Wek, Ent, File)) to quickly identify where to put the file.
Write plain SQL queries and execute them with the JPA API.
(Didn't think much about this one) Create a back reference from Wek and Ent to File (lazy loaded) and then you should be able to continue your first idea.
Don't know much about JPA, but about Postgres. And I would suggest this superior query:
SELECT *
FROM wek CROSS JOIN ent
LEFT JOIN fil USING (ent_id, wek_id);
You don't need the subselect.
The only difference in the result (besides being shorter and faster): You get the columns ent_id and wek_id once in the output (which might solve a problem with duplicated column names).
Should be easy to translate to JPA now.
I'm joining one table to another. The join works. I want to restrict the results to records with an "Error" message that can be in either table. When I do the following, I get no results back, yet I know there should be 2.
Criteria criteria = session.createCriteria(TableName.class);
criteria.createAlias("someList", "things");
Criterion restriction1 = Restrictions.eq("status", "Error");
Criterion restriction2 = Restrictions.eq("things.anotherStatus", "Error");
criteria.add(Restrictions.or(restriction1, restriction2));
finalList = criteria.list();
I noticed that the restrictions by themselves actually work. So, if I only do the first restriction on the original table with no alias OR if I only do the second restriction on the alias table, then I get 1 result each time.
Also, a simple join SQL query like the one below works as expected:
Select count(*)
From table1 t1
Left join table2 t2 on t1.id = t2.another_id
Where t1.status = 'ERROR' or t2.anotherStatus = 'ERROR'
How can I get this right in Hibernate?
EDIT 1: I now see that Hibernate does an Inner Join when I use the #JoinColumn annotation. How can I change it to do an Outer Join instead?
EDIT 2: Even adding #Fetch(FetchMode.JOIN) still results in an inner join! What gives? The documentation clearly says it will do an outer join. The annotation now looks like this:
#OneToMany
#JoinColumn(name="ID_FK")
#Fetch(FetchMode.JOIN)
private List<Thing> things;
Answer: use criteria.createAlias("someList", "things", JoinType.LEFT_OUTER_JOIN); instead.
Explanation: When no JoinType is specified, createAlias does an inner join by default.
Hi I'm trying to select records from one table which doesn't have records in connected many-to-many table with specific values.
I will explain on sample tables:
documentation:
id_documentation
irrelevant_data
user:
id_user
irrelevant_data
documentation_user:
id_documentation
id_user
role
What I want to achieve is to select every single documentation which doesn't have user in specific role. Any ideas?
The main problem is that I'm using java's CriteriaBuilder to create query so using subqueries is impossible (I think).
You can add restrictions on your left join using: createAlias(java.lang.String, java.lang.String, int, org.hibernate.criterion.Criterion) method, see API.
Check this answer for an example on how to use the left join with a criteria.
Main problem does not exist - Criteria API do have SubQuery. Query itself selects instances of User and uses not in construct to limit results based to subquery. Subquery selects all users that are connected to document with specific role via DocumentationUser.
Try something like this (code not tested):
CriteriaQuery<Documentation> cq = cb.createQuery(Documentation.class);
Root<Documentation> u = cq.from(Documentation.class);
Subquery<Integer> sq = cq.subquery(Integer.class);
Root<User> su = sq.from(User.class);
sq.select(su.get("id_user"));
Join<User, DocumentationUser> du = su.join("documentationUserCollection");
sq.where(cb.equals(du.get("role"), "mySpecificRole"));
cq.where(cb.not(cb.in(u.get("id_user")).value(sq)));
See also this useful answer on SO.
I am new to the Hibernate and HQL. I want to write an update query in HQL, whose SQL equivalent is as follows:
update patient set
`last_name` = "new_last",
`first_name` = "new_first"
where id = (select doctor_id from doctor
where clinic_id = 22 and city = 'abc_city');
doctor_id is PK for doctor and is FK and PK in patient. There is one-to-one mapping.
The corresponding Java classes are Patient (with fields lastName, firstName, doctorId) and Doctor (with fields doctorId).
Can anyone please tell what will be the HQL equivalent of the above SQL query?
Thanks a lot.
String update = "update Patient p set p.last_name = :new_last, p.first_name = :new_first where p.id = some (select doctor.id from Doctor doctor where doctor.clinic_id = 22 and city = 'abc_city')";
You can work out how to phrase hql queries if you check the specification. You can find a section about subqueries there.
I don't think you need HQL (I know, you ask that explicitly, but since you say you're new to Hibernate, let me offer a Hibernate-style alternative). I am not a favor of HQL, because you are still dealing with strings, which can become hard to maintain, just like SQL, and you loose type safety.
Instead, use Hibernate criteria queries and methods to query your data. Depending on your class mapping, you could do something like this:
List patients = session.CreateCriteria(typeof(Patient.class))
.createAlias("doctor", "dr")
.add(Restrictions.Eq("dr.clinic_id", 22))
.add(Restrictions.Eq("dr.city", "abc_city"))
.list();
// go through the patients and set the properties something like this:
for(Patient p : patients)
{
p.lastName = "new lastname";
p.firstName = "new firstname";
}
Some people argue that using CreateCriteria is difficult. It takes a little getting used to, true, but it has the advantage of type safety and complexities can easily be hidden behind generic classes. Google for "Hibernate java GetByProperty" and you see what I mean.
update Patient set last_name = :new_last , first_name = :new_first where patient.id = some(select doctor_id from Doctor as doctor where clinic_id = 22 and city = abc_city)
There is a significant difference between executing update with select and actually fetching the records to the client, updating them and posting them back:
UPDATE x SET a=:a WHERE b in (SELECT ...)
works in the database, no data is transferred to the client.
list=CreateCriteria().add(Restriction).list();
brings all the records to be updated to the client, updates them, then posts them back to the database, probably with one UPDATE per record.
Using UPDATE is much, much faster than using criteria (think thousands of times).
Since the question title can be interpreted generally as "How to use nested selects in hibernate", and the HQL syntax restricts nested selects only to be in the select- and the where-clause, I would like to add here the possibility to use native SQL as well. In Oracle - for instance - you may also use a nested select in the from-clause.
Following query with two nested inner selects cannot be expressed by HQL:
select ext, count(ext)
from (
select substr(s, nullif( instr(s,'.', -1) +1, 1) ) as ext
from (
select b.FILE_NAME as s from ATTACHMENT_B b
union select att.FILE_NAME as s from ATTACHEMENT_FOR_MAIL att
)
)
GROUP BY ext
order by ext;
(which counts, BTW, the occurences of each distinct file name extension in two different tables).
You can use such an sql string as native sql like this:
#Autowired
private SessionFactory sessionFactory;
String sql = ...
SQLQuery qry = sessionFactory.getCurrentSession().createSQLQuery(sql);
// provide an appropriate ResultTransformer
return qry.list();