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How do I retrieve the number of distinct rows with the JPA Criteria API

I need to count the number of rows returned by a CriteriaQuery. The relevant piece of information here is that those need to be distinct rows based on a dynamically selected set of columns.
This means, that I cannot count over the entire table, since that might consider results, that would be redundant if you strip a certain number of columns.
I have a List of Predicates and Selections to conform to:
private final List<Selection<?>> projection = new ArrayList<>();
private final List<Predicate> predicates = new ArrayList<>();
and I want to count the number of rows that would be returned, if this query was executed non-paginated:
criteriaQuery.multiselect(projection)
.distinct(true)
.where(cb.and(predicates.toArray(new Predicate[0])));
The usual approach of transforming this into a Subquery will not work, since you cant multiselect on a Subquery and also can't select from the Subquery.
Can this be done with the Criteria API?

can you try this ?
CriteriaBuilder builder = em.getCriteriaBuilder();
CriteriaQuery query = builder.createQuery(String.class);
Root ruleVariableRoot = query.from(RuleVar.class);
query.select(ruleVariableRoot.get(RuleVar_.varType)).distinct(true);
More infos: https://www.objectdb.com/java/jpa/query/criteria

How to join two Criteria Queries

I have a query that I want to make Criteria Query
select u.email, st.total_amount, st.company_total from users u
join (select user_id, SUM(balance) as total_amount,SUM(company_count) as company_total from subscription s
where s.is_active = 0
group by user_id) st on u.id = st.user_id
where u.is_active = 0
order by st.company_total
I have already made 1 criteria Query
CriteriaQuery<UserImpl> innerQuery = builder.createQuery(UserImpl.class);
Root<Subscription> subscriptionRoot = innerQuery.from(Subscription.class);
innerQuery.multiselect(subscriptionRoot.get("user").get("id"), builder.sum(subscriptionRoot.get("balance")),
builder.sum(subscriptionRoot.get("companyCount")));
I don't know how to make the outer query in spring hibernate JPA. Can some help.

Defining a JOIN clause is pretty simple. You first call the from method on your CriteriaQuery object to get a Root object. In the next step, you can call the join method to define your JOIN clause.
Following is example of Docs, you can manipulate it as per your example.
You can refer Hibernate docs for the join examples. following is sample code.
CriteriaQuery<String> q = cb.createQuery(String.class);
Root<Order> order = q.from(Order.class);
q.select(order.get("shippingAddress").<String>get("state"));
CriteriaQuery<Product> q2 = cb.createQuery(Product.class);
q2.select(q2.from(Order.class)
.join("items")
.<Item,Product>join("product"));
Docs to refer
Another quick example I found is listed below:
<Y> ListJoin<X, Y> join(ListAttribute<? super X, Y> list);
Quick example (assuming Employee has list of Tasks with many-to-many relation):
CriteriaQuery<Employee> query = criteriaBuilder.createQuery(Employee.class);
Root<Employee> employee = query.from(Employee.class);
ListJoin<Employee, Task> tasks = employee.join(Employee_.tasks);
query.select(employee)
.where(criteriaBuilder.equal(tasks.get(Task_.supervisor),
employee.get(Employee_.name)));
TypedQuery<Employee> typedQuery = entityManager.createQuery(query);
List<Employee> employees = typedQuery.getResultList();
Reference: here

Hibernate result list cast to get rows

Hello I had problem with iterate Hibernate ResultList
I had followed query that I got from external class:
queryContent = "select distinct c.identity, c.number, c.status, ctr.name, aab.paymentConditions.currency from AgreementStateBean ast join ast.currentAgreement aab join conagr.contract c where c.agreementStateId = ? and con.mainContractor = true ? "
And I must sum whole aab.paymentConditions.currency, check numbers of statutes and names.
I want to do this by iterate list of results:
Query q = session.createQuery(queryContent);
List result = q.list();
Long wholeCurrency, numberOfStatutes;
for(Object res : result){
//wholeCurrency += res.getColumnName?
}
My question is how to cast res Object to have possibility to get concrete column values? I had read about create map inside hibernate query but I don't know it is good practice to modyfied query string by adding
"new map(" prefix and then ")"
before from sql statement
Solution:
After All I decided to use map in my query. I modified my external query by adding hibernate map statement by replacing select by 'select new map(' and from by ') from'.
Additional thing is to add 'as' statement with name of key because without them column keys are integer.
So after all my query looks like follow:
"select new map( distinct c.identity, c.number, c.status as status, ctr.name as name, aab.paymentConditions.currency as currency ) from AgreementStateBean ast join ast.currentAgreement aab join conagr.contract c where c.agreementStateId = ? and con.mainContractor = true ? "
That was the most siutable solution for me, I tried with 'NEW com.example.MyClass' as Kostja suggested but in my case I didn't have control for incoming query so I can not rely on pernament constructor.
new List( select...
Is also interest but it also didn't tell me on with position I have my field that give me information.

If I understand correctly, you want to have a typed representation of your result without it being an entity itself. For this, you can use constructor queries:
"SELECT NEW com.example.MyClass( e.name, e.data) FROM Entity e"
MyClass has to have a matching constructor. Full qualification (com.example) is not mandatory AFAIK.
If you are using this query often, creating a view in the DB may be a good idea. You can map a view to an entity just as if it were a regular table, but please note that you cannot store changes to you data over a mapped view.
EDIT: Turns out, mapping to an unspecified Map is alright with Hibernate:
select new map( mother as mother, offspr as offspr, mate as mate )

As per http://docs.jboss.org/hibernate/orm/4.2/devguide/en-US/html/ch11.html#ql-select-clause
you can use
queryContent = "select new list(distinct c.identity, c.number, c.status, ctr.name, aab.paymentConditions.currency) from AgreementStateBean ast join ast.currentAgreement aab join conagr.contract c where c.agreementStateId = ? and con.mainContractor = true ? "
And you get List<List> as result.

Dynamic search using sql queries

I'm implementing dynamic search within my application, I have the following options to build a query.
String concatenation from the user input
Use multiple Queries, and pull the right query based on the user input
Use one query, use wild cards for the inputs not given by the user.
eg:
select * from A,B where a.id like nvl( {input}, '%')
and a.id = b.aid
and b.value like nvl({input2},'%');
Because id is a primary key I get the following error in the oracle when tried.

Firstly, for wildcard search you need to use the LIKE predicate, not =. Secondly, you can't use the LIKE predicate for numeric data, obviously. What you can do is this:
select * from A,B where ( a.id = {input} or {input} is null )...

A simple solution could be:
StringBuffer sqlSB = new StringBuffer("select * from A,B where a.id = b.aid ");
if(input!=null&&!input.equals("")){
sqlSB.append(" and a.id = ").append(input);
}
if(input2!=null&&!input2.equals("")){
sqlSB.append(" and b.value = '").append(input2).append("' ");
}

criteria query fails group by because of single qoutes?

I came accross an interesting behaviour: probably criteria API puts single quotes around parameters in query.
CriteriaBuilder criteriaBuilder = em.getCriteriaBuilder();
CriteriaQuery<SomeClass> criteriaQuery = criteriaBuilder.createQuery(SomeClass.class);
Metamodel metamodel = em.getMetamodel();
EntityType<SomeClass> entityType_ = metamodel.entity(SomeClass.class);
Root<SomeClass> root = criteriaQuery.from( SomeClass );
criteriaQuery.select(root.get(entityType_.getSingularAttribute( "someField" ));
TypedQuery<SomeClass> q = em.createQuery(criteriaQuery);
List<SomeClass> result = (List<SomeClass>) q.getResultList();
this snippet results in a list with one column which is full of with "someField" in every single cells of the column. (select 'someField' from SomeClass; <--really works )
The select accepts this behaviour by criteria, however the group by fails, says: ORA-00979: not a GROUP BY expression.
I only think about criteria does the same substitution, like in case of select.
criteriaQuery.groupBy(root.get(entityType_.getSingularAttribute("someField") ));
How can I avoid those single qoutes in my queries?
Any suggests appreciated, thank You in advance.