I have a method:
public List<Timetable> getTimetableTableForRegion(String id) {
List<Timetable> timetables;
TypedQuery<Timetable> query = em_read.createQuery("SELECT ..stuff.. where R.id = :id", Timetable.class).setParameter("id", Long.parseLong(id));
timetables = query.getResultList();
return timetables;
}
which returns this:
so, what am I missing in order to return a list of Timetable's?
ok, so, ..stuff.. part of my JPQL contained an inner join to other table. Even through in SELECT there were selected fields just from one table, which was used as type - Timetable, Eclipslink was unable to determine if this fields are part of that entity and instead of returning list of defined entity returned list of Object[].
So in conclusion: Use #OneToMany/#ManyToOne mappings (or flat table design) and query just for ONE table in your JPQL to be able to typize returned entities.
Not sure it might be something is looking for, but I had similar problem and converted Vector to ArrayList like this:
final ArrayList<YourClazz> results = new ArrayList<YourClazz>();;
for ( YourClazzkey : (Vector<YourClazz>) query.getResultList() )
{
results.add(key);
}
i have faced the same problem. and my entity has no one to one or one to many relationship. then also jpql was giving me queryresult as vector of objects. i changed my solution to query to criteria builder. and that worked for me.
code snippet is as below:
CriteriaBuilder builder = this.entityManager.getCriteriaBuilder();
CriteriaQuery<Timetable> criteria = builder.createQuery(Timetable.class);
Root<Enumeration> root = criteria.from(Timetable.class);
criteria.where(builder.equal(root.get("id"), id));
List<Timetable> topics = this.entityManager.createQuery(criteria) .getResultList();
return topics;
Related
I am using GroupBy in my LINQ queries. My query is working fine, except my foreign key objects are missing. Then, I tried to add Include in my query. Following is my code:
public ActionResult GetEmployees()
{
var Emloyees = db.Employees.AsQueryable();
Emloyees.GroupBy(e=> new {e.JobTitleId, e.GenderId})
.Select(tr => new MyObject
SalaryTotal = tr.Sum(r=>r.Salary)
}).Include(tr=>tr.JobTitle).Include(tr=>tr.Gender).ToList();
}
I am getting this exception:
The result type of the query is neither an EntityType nor a CollectionType with an entity element type. An Include path can only be specified for a query with one of these result types.
I tried to add it before GroupBy and directly in db.Employees.AsQueryable(), but nothing worked. What am I doing wrong?
The problem is that you are doing a projection with the .Select(...), after which your includes cannot be resolved. The result of that query will be a list MyObject, which does not work for includes that are actually on Employee.
So Try it like this:
Emloyees
.GroupBy(e=> new {e.JobTitleId, e.GenderId})
.Select(tr => new MyObject {
SalaryTotal = tr.Sum(r=>r.Salary),
JobTitle = tr.FirstOrDefault().JobTitle,
Gender = tr.FirstOrDefault().Gender
}).ToList();
You will have to extend MyObject with 2 additional properties, but the result of your query will be what you want (I assume).
UPDATE:
I understood that the solution to my problem is doing subqueries, which apply a different filter each time, and they have a reduced result set. But I can't find a way to do that in MyBatis logic. Here is my query code
List<IstanzaMetadato> res = null;
SqlSession sqlSession = ConnectionFactory.getSqlSessionFactory().openSession(true);
try {
IstanzaMetadatoMapper mapper = sqlSession.getMapper(IstanzaMetadatoMapper.class);
IstanzaMetadatoExample example = new IstanzaMetadatoExample();
Iterator<Map.Entry<Integer, String>> it = map.entrySet().iterator();
while (it.hasNext()) {
Map.Entry<Integer, String> entry = it.next();
example.createCriteria().andIdMetadatoEqualTo(entry.getKey()).andValoreEqualTo(entry.getValue());
}
example.setDistinct(true);
res = mapper.selectByExample(example);
I need to execute a new selectByExample but inside the while cycle, and it has to query the previus "SELECTED" results....
Is there a Solution ?
ORIGINAL QUESTION:
I have this table structure
I have to select rows from the table with different filters, specified by the final user.
Those filters are specified by a couple (id_metadato, valore), in example you can have id_metadato = 3 and valore = "pippo";
the user can specify 0-n filters from the web page typing 0-n values inside the search boxes which are based on id_metadato
Obviusly, the more filters the users specifies, the more restriction would have the final query.
In example if the user fills only the first search box, the query will have only a filter and would provide all the rows that will have the couple (id_metadato, valore) specified by the user.
If he uses two search boxes, than the query will have 2 filters, and it will provide all the rows that verify the first condition AND the second one, after the "first subquery" is done.
I need to do this dinamically, and in the best efficient way. I can't simply add AND clause to my query, they have to filter and reduce the result set every time.
I can't do 0-n subqueries (Select * from ... IN (select * from ....) ) efficiently.
Is there a more elegant way to do that ? I'm reading dynamic SQL queries tutorials with MyBatis, but I'm not sure that is the correct way. I'm still trying to figure out the logic of the resosultio, then I will try to implement with MyBatis.
Thanks for the answers
MyBatis simplified a lot this process of nesting subqueries, it was sufficient to concatenate the filter criterias and to add
the excerpt of the code is the following
try {
IstanzaMetadatoMapper mapper = sqlSession.getMapper(IstanzaMetadatoMapper.class);
IstanzaMetadatoExample example = new IstanzaMetadatoExample();
Iterator<Map.Entry<Integer, String>> it = map.entrySet().iterator();
while (it.hasNext()) {
Map.Entry<Integer, String> entry = it.next();
if (listaIdUd.isEmpty()) {
example.createCriteria().andIdMetadatoEqualTo(entry.getKey()).andValoreEqualTo(entry.getValue());
example.setDistinct(true);
listaIdUd = mapper.selectDynamicNested(example);
continue;
}
example.clear();
example.createCriteria().andIdMetadatoEqualTo(entry.getKey()).andValoreEqualTo(entry.getValue()).andIdUdIn(listaIdUd);
example.setDistinct(true);
listaIdUd = mapper.selectDynamicNested(example);
}
Lets say I have the following JPQL query
SELECT e.column1, e.column2, SUM(e.column3), SUM(e.column4) FROM Entity e GROUP BY e.column1, e.column2
Obviously I wont be returning an Entity object but something a bit more complex. How do I return this in the method?
public List<???> query1() {
Query q = entityManager.createQuery("...");
List<Something???> list = q.getResultList();
return list;
}
Such a query returns a List<Object[]>, where each element is thus an array of Objects. The first element of the array will have the type of Entity.column1, the second one will have the type of Entity.column2, and the last 2 ones will be (with Hibernate at least) of type Long (check with EclipseLink).
It's up to you to transform the List<Object[]> in a List<Foo>, by simply looping over the list of objects and transforming each one into a Foo. You may also use the constructor notation directly in the query (provided Foo has such a constructor), but I personally dislike it, because it isn't refactorable:
select new com.baz.bar.Foo(e.column1, e.column2, SUM(e.column3), SUM(e.column4)) from ...
I have a statement:
var items = from e in db.Elements
join a in db.LookUp
on e.ID equals a.ElementID
where e.Something == something
select new Element
{
ID = e.ID,
LookUpID = a.ID
// some other data get populated here as well
};
As you can see, all I need is a collection of Element objects with data from both tables - Elements and LookUp. This works fine. But then I need to know the number of elements selected:
int count = items.Count();
... this call throws System.NotSupportedException:
"The entity or complex type 'Database.Element' cannot be constructed in a LINQ to Entities query."
How am I supposed to select values from multiple tables into one object in Entity Framework? Thanks for any help!
You are not allowed to create an Entity class in your projection, you have to either project to a new class or an anonymous type
select new
{
ID = e.ID,
LookUpID = a.ID
// some other data get populated here as well
};
Your code doesn't work at all. The part you think worked has never been executed. The first time you executed it was when you called Count.
As exception says you cannot construct mapped entity in projection. Projection can be made only to anonymous or non mapped types. Also it is not clear why you even need this. If your class is correctly mapped you should simply call:
var items = from e in db.Elements
where e.Something == something
select e;
If LookupID is mapped property of your Element class it will be filled. If it is not mapped property you will not be able to load it with single query to Element.
I am trying to use subqueries in an application I am writing using JPA 2.0 type-safe criteria API, with Hibernate 3.6.1.Final as my provider. I have no problem selecting primitive types (Long, MyEntity, etc.), but I want to select multiple columns.
Here's an example of something completely reasonable. Ignore the needless use of subquery -- it is simply meant as illustrative.
EntityManager em = getEntityManager();
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Tuple> cq = cb.createTupleQuery();
Subquery<Tuple> subQ = cq.subquery(Tuple.class);
Expression<Long> subqCount;
{
Root<MyEntity> root = subQ.from(MyEntity.class);
Path<MyEntity> filter = root.get(MyEntity.challenge);
subqCount = cb.count(root);
// How to select tuple?
Selection<Tuple> tuple = cb.tuple(filter, subqCount);
// !! Run-time exception here
Expression<Tuple> tupleExpr = (Expression<Tuple>) tuple;
// Not sure why I can't use multiSelect on a subQuery
// #select only accepts Expression<Tuple>
createSubQ.select(tupleExpr);
createSubQ.groupBy(filter);
}
cq.multiselect(subqCount);
Although the compiler doesn't complain, I still get a run-time exception.
java.lang.ClassCastException: org.hibernate.ejb.criteria.expression.CompoundSelectionImpl cannot be cast to javax.persistence.criteria.Expression
Is this a bug in hibernate, or am I doing something wrong?
If you can't use multiselect on a subquery, then how can you perform a groupBy?
If you can't use groupBy on a subquery, why is it in the API?
I have the same problem.
I can only attempt to answer your last question by saying you can only really use sub queries to perform very simple queries like:
SELECT name FROM Pets WHERE Pets.ownerID in (
SELECT ID FROM owners WHERE owners.Country = "SOUTH AFRICA"
)
The other thing I wanted to say was how much this incident reminds me of xkcd #979.
I had similar problem.
I had specification, and I wanted to get ids of objects matching this specification.
My solution:
CriteriaBuilder criteriaBuilder = em.getCriteriaBuilder();
CriteriaQuery<Tuple> tupleCriteriaQuery = criteriaBuilder.createTupleQuery();
Root<Issue> root = tupleCriteriaQuery.from(Issue.class);
tupleCriteriaQuery = tupleCriteriaQuery.multiselect(root.get(IssueTable.COLUMN_ID));//select did not work.
tupleCriteriaQuery = tupleCriteriaQuery.where(issueFilter.toPredicate(root, tupleCriteriaQuery, criteriaBuilder));
List<Tuple> tupleResult = em.createQuery(tupleCriteriaQuery).getResultList();
First I select columns (In my case I need only one column), and then I call where method to merge with my given specification.