I am using hibernate 5 (I am not familiar with hibernate, just started with it) and I want to perform a simple select query, after searching I found the following code to select an element by id:
CriteriaBuilder cb = session.getCriteriaBuilder();
CriteriaQuery<Ord> query = cb.createQuery(MyClass.class);
Root<Ord> root = query.from(MyClass.class);
query.select(root);
query.where(cb.equal(root.get(MyClass.NUM),ordId));
Query<Ord> sessionQuery = session.createQuery(query);
return sessionQuery.getSingleResult();
I find it a heavy way to just get just one element.
The question is: Is the above the recommended/correct way to fetch data using hibernate (5)?
Thanks in advance,
JPQL provides us with a quicker and simpler implementation while using the Criteria API is more dynamic and robust.
public List<Student> findAllStudentsWithJpql() {
return session.createQuery("SELECT a FROM Student a", Student.class).getResultList();
}
You are using Criteria API
The Criteria API provides a dynamic approach for building JPA queries.
public List<Student> findAllStudentsWithCriteriaQuery() {
CriteriaBuilder cb = session.getCriteriaBuilder();
CriteriaQuery<Student> cq = cb.createQuery(Student.class);
Root<Student> rootEntry = cq.from(Student.class);
CriteriaQuery<Student> all = cq.select(rootEntry);
TypedQuery<Student> allQuery = session.createQuery(all);
return allQuery.getResultList();
}
Above two methods are the common way in Hibernate.
Documentation - https://docs.jboss.org/hibernate/orm/5.2/userguide/html_single/Hibernate_User_Guide.html
You can perform something like this...
#Autowired
private SessionFactory session;
Query<Your Class> query = session.getCurrentSession().createQuery("select * from <tableName>);
Related
The scenario is:
Entity Student
ID
Name
List Courses
Entity Course
ID
Name
Student
Now I need the list of students who are studying course 'Programming'
How can I achieve this using Criteria Query.
try this:
CriteriaBuilder cb = entityManager.getCriteriaBuilder();
CriteriaQuery<Student> cq = cb.createQuery(Student.class);
Root<Student> rootStudent = cq.from(Student.class);
Join<Student,Course> joinCourse = rootStudent.join("courses",JoinType.INNER);
cq.where(cb.equals(joinCourse.get("Name"),"Proggraming"));
cq.select(rootStudent);
List<Student> res = entityManager.createQuery(cq).getResultList();
In this example I assume that you have the JPA entities well modeled, including bidirectional relationships. It would also be recommended if it is for an API that you use pojos instead of returning a JPA entity to the web part, for this you should use multiselect instead of select and specify each of the fields you want to obtain, but as a first approximation it would be valid.
It would also be advisable to use metamodels for JPA entities instead of accessing the properties through a string with the name (join, get methods ..)
In this scenario, it does not make sense to make a subquery, I change the query to find the students of the courses Proggraming1 or Proggraming2 through a subquery(I would still prefer to do it by filtering the joins without using subquery), it would be something like this:
CriteriaBuilder cb = entityManager.getCriteriaBuilder();
CriteriaQuery<Student> cq = cb.createQuery(Student.class);
Root<Student> rootStudent = cq.from(Student.class);
Join<Student,Course> joinCourse = rootStudent.join("courses",JoinType.INNER);
Subquery<Long> subqueryIdCourse = cq.subquery(Long.class);
Root<Course> rootCourseSq = subqueryIdCourse.from(Course.class);
subqueryIdCourse.where(
cb.or(
cb.equals(rootCourseSq.get("Name"),"Proggraming1"),
cb.equals(rootCourseSq.get("Name"),"Proggraming2")))
subqueryIdCourse.select(rootCourseSq.get("ID"))
cq.where(joinCourse.get("ID").in(subqueryIdCourse.getSelection()));
cq.select(rootStudent);
List<Student> res = entityManager.createQuery(cq).getResultList();
Let's say, I have a query like
Select a.valA, b.valB
from tableA a join tableB b on a.joinCol = b.joinCol
where a.someCol = 1.
I want to execute it using Hibernate (and Spring Data) in one query to the database. I know, I can write just
Query query = em.createQuery(...);
List<Object[]> resultRows = (List<Object[]>)query.getResultList();
But my question would be - is it possible to do it in a typesafe way, using CriteriaQuery for example? The difficulty is, that, as you see, I need to select values from different tables. Is there some way to do this?
Simple example where an Employee has many to many relation to several jobs that he may have :
CriteriaBuilder builder = session.getCriteriaBuilder();
CriteriaQuery<Tuple> criteria = builder.createTupleQuery();
Root<TableA> root = criteria.from(TableA.class);
Path<Long> qId = root.get("id");
Path<String> qTitle = root.get("title");
Join<TableA, TableB> tableTwo = root.join("joinColmn", JoinType.INNER);
criteria.multiselect(qId, qTitle, tableTwo);
List<Tuple> tuples = session.createQuery(criteria).getResultList();
for (Tuple tuple : tuples)
{
Long id = tuple.get(qId);
String title = tuple.get(qTitle);
TableB tableB= tuple.get(tableTwo);
}
but saw that there is an alternate answer here :
JPA Criteria API - How to add JOIN clause (as general sentence as possible)
Im trying to build using CriteriaBuilder the following query :
SELECT * FROM job j, asset a, asset_users au
where j.JOB_ID = a.ASSET_ID and a.ASSET_ID = au.ASSET_ID and au.USER_ID = 6
Where job has an asset and asset has a list of users...
I want to return just the list of jobs which have a asset that contains a given user...
I saw some guys doing it like that :
Session session = this.sessionFactory.getCurrentSession();
Criteria criteria = session.createCriteria(Company.class);
criterion = Restrictions.eq("companyRoles.name", "ADMIN");
criteria.add(criterion);
List<Company> companyList = criteria.list();
Tried to replicate that to criteriabuilder but got no luck. All i was getting is that it couldn't find my user id inside an object list (userList). Guess my example is harder because you have to access the object like (job).asset.userList.id .
BTW, tried this as well :
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Job> cq = cb.createQuery(Job.class);
Root<Job> jobRoot = cq.from(Job.class);
Join<Job, User> assetJoin = jobRoot.join("asset.userList");
cq.where(assetJoin.get("id").in(id));
got same issue... couldn't find the path.
Any help is very much appreciated!
Thanks
I think you are missing a step. You need the next level of joining.
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Job> cq = cb.createQuery(Job.class);
Root<Job> jobRoot = cq.from(Job.class);
// join the asset
Join<Job, Asset> assetJoin = jobRoot.join("asset");
// join the list of users
Join<Asset, User> assetUserJoin = assetJoin.join("userList");
cq.where(assetUserJoin.get("id").in(id));
The type of assetUsrJoin.get("id") is Path<Long> or something similar. JPA Criteria API
I have a view named V_ENTITY in my database which is populated with a few entries. Using SQL scrapbook in Eclipse I can easily do queries which return desired results.
However, when I try to retrieve the entries from my DAO class, I get nothing. My count returns 0 as number of entries, while there are 7 of them, which I can fetch with native SQL queries via scrapbook.
I have created a separate entity for that particular view:
#Entity
#Table(name = "V_ENTITY")
public class ViewEntity {
...
}
I use JPA2 CriteriaQuery API for dynamic queries I do. Here is the example for count that is bugging me:
CriteriaBuilder cb = entityManager.getCriteriaBuilder();
CriteriaQuery<ViewEntity> transactionQuery = cb.createQuery(ViewEntity.class);
Root<ViewEntity> ViewEntityRoot = transactionQuery.from(ViewEntity.class);
Predicate[] predicates = new Predicate[<someSize>]
predicates[<someIndex>] = cb.equal(
root.get("foreignName").as(String.class),
"%" + foreignName + "%"
)
CriteriaQuery<Long> countQuery = cb.createQuery(Long.class);
countQuery.select(cb.count(ViewEntityRoot));
countQuery.where(predicates);
TypedQuery<Long> finalQuery = entityManager.createQuery(countQuery);
return finalQuery.getSingleResult().intValue();
Can anyone help me find a flaw in my code/thinking?
Use the <property name="show_sql">true</property> property to show us the generated sql pls
I am trying to write following SQL query using JPA Criteria API
SELECT * FROM roles WHERE roles.name IN (SELECT users.role FROM users where name="somename");
and it is a bit to much for me (I have just started learing Criteria API). I got something like this:
CriteriaBuilder criteriaBuilder = manager.getCriteriaBuilder();
CriteriaQuery<RoleEntity> criteriaQuery = criteriaBuilder.createQuery(RoleEntity.class);
Root<RoleEntity> root = criteriaQuery.from(RoleEntity.class);
Subquery<UserEntity> subquery = criteriaQuery.subquery(UserEntity.class);
Root<UserEntity> subqueryRoot = subquery.from(UserEntity.class);
subquery.where(criteriaBuilder.equal(subqueryRoot.get(UserEntity_.username), username));
subquery.select(subqueryRoot);
And I have no idea how to put it all together.
Best regards,
Bartek
Fellow JPA learner here. Here's my attempt at setting it up:
// Get the criteria builder from the entity manager
CriteriaBuilder cb = manager.getCriteriaBuilder();
// Create a new criteria instance for the main query, the generic type indicates overall query results
CriteriaQuery<RoleEntity> c = cb.createQuery(RoleEntity.class);
// Root is the first from entity in the main query
Root<RoleEntity> role = criteriaQuery.from(RoleEntity.class);
// Now setup the subquery (type here is RETURN type of subquery, should match the users.role)
Subquery<RoleEntity> sq = cb.subquery(RoleEntity.class);
// Subquery selects from users
Root<UserEntity> userSQ = sq.from(UserEntity.class);
// Subquery selects users.role path, NOT the root, which is users
sq.select(userSQ.get(UserEntity_.role))
.where(cb.equal(userSQ.get(UserEntity_.username), username)); // test for name="somename"
// Now set the select list on the criteria, and add the in condition for the non-correlated subquery
c.select(role)
.where(cb.in(role).value(sq)); // can compare entities directly, this compares primary key identities automatically
Hopefully that helps!