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Hibernate Criteria: How to reset projection

I need to select products based on tags, here are the tables
products: productId, name, description, price, etc
tags: tagId, name
product_tags: productId, tagId
and I have 2 classes Product and Tag and relation is specified in Product class
#OneToMany(cascade = CascadeType.DETACH)
#JoinTable(
name = "product_tags",
joinColumns = #JoinColumn(name = "productId"),
inverseJoinColumns = #JoinColumn(name = "tagId")
)
public List getTags() {
return tags;
}
public void setTags(List tags) {
this.tags = tags;
}
Please note I only want to select products and not tags. following works fine
Criteria cri = getSession().createCriteria(Product.class);
cri.setFirstResult(index);
cri.setMaxResults(limit);
return cri.list();
As I am trying to get list for pagination, so I need total number of pages that can be retrieved by getting totalRecords/recordPerPage
Criteria cri = getSession().createCriteria(Product.class);
//add any required filter to criteria
//e.g cri.add(Restrictions.like("name", keyword, MatchMode.ANYWHERE));
//********** Following code is in utility function ******************/
//Get total number of records matching criteria
cri.setProjection(Projections.rowCount());
Long totalRecords = (Long)cri.uniqueResult();
//Get paginated records
cri.setProjection(null);// This is evil but works
cri.setFirstResult(index);
cri.setMaxResults(limit);
paginatedRecords = cri.list();
Question 1: Is it possible to set some thing like cri.setProjection(Product.class) instead of setting it null, I am aware that I can create a projection list and add all the column of product class but that seems overkill + the common part is in utility function and I found no way to retrieve the previous projection. cri.getProject()
Why I need another method because cri.setProjection(null) fails when I apply join, because it will project all the column of products, tags, product_tags. which cannot be casted to List
Get all products that have associated tag ids as (4,5,6)
cri.createAlias("tags", "t");
cri.add(Restrictions.in("t.tagId", new Integer[]{4,5,6}));
Here is the issued query
select
this_.productId as productId1_9_1_,
this_.categoryId as category6_9_1_,
this_.description as descript8_9_1_,
this_.name as name13_9_1_,
tags3_.productId as productId1_9_,
t1_.tagId as tagId2_10_,
t1_.tagId as tagId1_11_0_,
t1_.name as name4_11_0_,
from
products this_
inner join
product_tags tags3_
on this_.productId=tags3_.productId
inner join
tags t1_
on tags3_.tagId=t1_.tagId
where t1_.tagId in (4,5,6) limit 25
I have found a work-around for this as follows
cri.setProjection(null)
criteria.setResultTransformer(CriteriaSpecification.DISTINCT_ROOT_ENTITY)
This will fix type cast exception.
Question 2: The back-end query is still the same, it join and project all the columns of all involved tables. ((Yakkh dirty)), Why the same query?, I am expecting projections on Product class only

Retrieveing list from a many-to-many relation with JPA/HQL

I have 3 classes, I am trying to get a list of all the events of an eventhost that a user is subscribed to. I am probably thinking way too complicated but I have very little experience with JPA/HQL.
User class
#ManyToMany
#JoinTable(name = "Subscriptions", joinColumns = #JoinColumn(name = "user_id", referencedColumnName = "id") , inverseJoinColumns = #JoinColumn(name = "event_host_id", referencedColumnName = "id") )
private List<EventHost> subscriptions;
EventHost class
#OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
#JoinColumn(name = "event_host_id", referencedColumnName = "id", updatable = true)
private List<Event> events;
I tried using this query, but it tells me that subscriptions is not mapped, which it is not since it's not a java class.
String hql = "SELECT o FROM Event WHERE event_host_id IN (SELECT a FROM EventHost WHERE id IN(SELECT b FROM User WHERE = + " + userid + "))";
I know injecting the userid like this is bad practice, I'm just doing it for testing purposes.
Please ask if you need something more, I would really like to understand how to write a query for this.

This question should really be HQL with two join tables, but I'll let you change it. Since its HQL, or JPA, it's database independent.
Anyway, any time you see a OneToMany or ManyToMany relationship you have a join table and so you should be thinking joins. It's always a good idea to look at the sql create table statements to see what's going on. In this case your user_subscriptions join table is:
create table user_subscriptions (user_id integer not null, subscriptions_id integer not null)
and your event_host_events join table is this:
create table event_host_events (event_host_id integer not null, events_id integer not null)
Nothing new there. When you're trying to get something new working that you don't intuitively understand, break it down into things you can do. For example, you can execute two queries, getting a Users subscriptions first, and then getting the Events for those subscriptions:
Query query = session.createQuery("select u.subscriptions from User u where name = :name");
query.setParameter("name", name);
List<EventHost> subscriptions = query.list();
List<Event> events = new ArrayList<Event>();
Query query2 = session.createQuery("select s.events from EventHost s where id = :id");
for (EventHost s: subscriptions ) {
query2.setParameter("id", s.getId());
events.addAll( query2.list());
}
Not elegant, but it works. Then, keeping join in mind, figure out how to make one statement out of the two of them.
Query query = session.createQuery("select s.events from User u join u.subscriptions s where u.name = :name)");
query.setParameter("name", name);
return query.list();
The join will use an inner join by default, so you're ok there. The JPA provider will auto-magically join your three Entity tables and two Join Tables for you:
select
event4_.id as id1_2_
from user user0_
inner join user_subscriptions subscripti1_ on user0_.id=subscripti1_.user_id
inner join event_host eventhost2_ on subscripti1_.subscriptions_id=eventhost2_.id
inner join event_host_events events3_ on eventhost2_.id=events3_.event_host_id
inner join event event4_ on events3_.events_id=event4_.id
where user0_.name=?
Aren't you glad you don't have to write that query?

HQL Query not executing

I have 2 tables Asset and Asset_Dist_Types. Asset is parent and Asset_Dist_Types is a child table. Asset_Dist_Types is having 2 columns asset_id and lkp_dist_type where asset_id is the primary key in Asset table. In Asset_Dist_Types it is a many to many (one asset_id can have multiple lkp_dist_type entries.) In java, we have entity class only for Asset table. In that for Asset_Dist_Type, they have mentioned it as collection of elements. In Asset.java, entry for Asset_Dist_Type is as follows.
#CollectionOfElements
#JoinTable(name = "ASSET_DIST_TYPE", joinColumns = #JoinColumn(name="ASSET_ID"))
#Column(name="LKP_DIST_TYPE")
private Set<Integer> distTypes = new LinkedHashSet<Integer>(0);
Now I would like to update Asset_Dist_Type table's lkp_dist_type column. I have list of asset id's. I have written following query to update it.
int hql = entityManager.createQuery(
"update Asset a set a.distTypes = :distTypeParamId where a.assetId in (:assetIdParam)")
.setParameter("distTypeParamId", distTypeList)
.setParameter("assetIdParam", assetIdListToUpdateLOB)
.executeUpdate();
But this is throwing
javax.persistence.PersistenceException:
org.hibernate.exception.GenericJDBCException: could not execute update query.
Since I am new to hibernate I am not getting what is the solution. Can someone please help me?

Solved it by following a different way.. I got list of asset id's and list of distribution types. I iterated over the list of asset id's and for each asset id I added list of distribution types and flushed it. It is working now..!
After getting list of asset id's
for(int i=0;i<assetIdListToUpdateLOB.size();i++){
int assetId = assetIdListToUpdateLOB.get(i);
System.out.println(assetId);
List<Asset> assetDetailsList = entityManager
.createQuery(
"select distinct asset from Asset asset "
+ "left join fetch asset.distTypes dt "
+ "where asset.assetId = :assetIdParam")
.setParameter("assetIdParam", assetId).getResultList();
if(assetDetailsList.size()>0){
this.asset = assetDetailsList.get(0);
asset.getDistTypes().clear();
asset.getDistTypes().addAll(selectedDistributionTypes);
entityManager.flush();
}
}

JPQL distinct with string function

I have a JPQL like this one:
select distinct d
from Department d
left join fetch d.employees
When I want to fetch one of the lazy property of my Department entity, the distinct is not working any more.
select distinct d, substring(d.htmlDescription, 1,400)
from Department d
left join fetch d.employees
The query returns as much Department as the number of employees in it.
The substring(d.htmlDescription) is important because the property is defined as a CLOB (type TEXT under postgresql):
#Column(columnDefinition = "TEXT")
#Basic(fetch = FetchType.LAZY)
String htmlBody;
The substring function is translated in sql thus limiting the amount of data transfered beetween the database and the web server.
As a workaround, I tried to break the query in two parts : 
select d, substring(d.htmlDescription, 1,400)
from Department d where d in (
select distinct d1
from Department d1 left join fetch d1.employees
)
This doestn't work because the JOIN FETCH must not be used in the FROM clause of a subquery.

Finally I found a solution to my problem by :
modifying my mapping
cutting the request in 2 calls.
The htmlBody field is now in another entity. Thus the departement entity is lighter.
class Department{
...
#OneToOne (fetch = FetchType.LAZY,
cascade = {CascadeType.PERSIST, CascadeType.MERGE, CascadeType.REMOVE})
Content content = new Content();
...
}
class Content{
...
#Column(columnDefinition = "TEXT")
#Basic(fetch = FetchType.LAZY)
String htmlBody;
...
}
I can then use the following requests :
List<Department> deps = em.get().createQuery(
"select distinct d " +
"from Department d " +
"order by d.id desc ", Department.class)
.setFirstResult(first)
.setMaxResults(count)
.getResultList();
List<Object[]> tuple = em.get().createQuery(
"select d, substring(d.content.htmlBody, 1,400)" +
"from Department d " +
"left join fetch d.employees" +
"where d in (:deps) order by d.id desc")
.setParameter("deps", deps)
.getResultList();
... //Filter the duplicates due to the fetching
That way, I have 2 sql queries. The fetching of employees is done in the second query witch occurs on a small amount of datas. The substring is realized in SQL. Perfect!

Since I cannot make comments, I would like to point out few things that stick out to me as doubtfull.
What is the object returned with distinct d, substring(d.htmlDescription, 1,400)? Could you fetch that String with separate query, or get that substing using Java?
I would trust that that query can be rewritten into one without left join statement.
Maybe you could rewrite the query so you could put substring statement first and then distinct d?

Fetching join using #JoinTable with SQLQuery

I have a mapped entity with a property "latestHistory", which is mapped through a join table, like:
class Record {
#OneToOne(cascade = { CascadeType.MERGE, CascadeType.PERSIST, CascadeType.REMOVE }, fetch = FetchType.LAZY, optional = true)
#JoinTable(name = "latest_history_join_view", joinColumns = { #JoinColumn(name = "record_id") }, inverseJoinColumns = { #JoinColumn(name = "history_id") })
#AccessType("field")
public History getLatestHistory() { ... }
}
The mapping works correctly when I call myRecord.getLatestHistory().
I have a complex native SQL query, which returns a batch of Records, and joins on the History for each record using the join table. I want to return Record entites from the query, and have the History objects populated in the result. My attempt looks like this:
StringBuffer sb = new StringBuffer();
sb.append("select {r.*}, {latestHistory.*}");
sb.append(" from record r");
sb.append(" left join latest_history_join_view lh on lh.record_id = r.record_id");
sb.append(" left join history latestHistory on latestHistory.history_id = lh.history_id");
SQLQuery query = session.createSQLQuery(sb.toString());
query.addEntity("r", Record.class).addJoin("latestHistory", "r.latestHistory");
When I do this, it generates a query like:
select
r.record_id, r.name...,
r_1.history_id, --this part is wrong; there is no such alias r_1
latestHistory.history_id, latestHistory.update_date, ...
from record r
left join latest_history_join_view lh on lh.record_id = r.record_id
left join history latestHistory on latestHistory.history_id = lh.history_id
How can I get it to join correctly and fetch my association, without messing up the select list?
[Update: some of the approaches that I've tried:
select {r.*}, {latestHistory.*} -> SQL error, generates a wrong column name "r_1.history_id"
select {r.*}, {anyOtherEntityAssociatedToR.*} -> wrong column name (as above)
select {r.*}, {r.history_id}, {latestHistory.*} -> hibernate error, r has no history_id column
select r.*, lh.history_id as history_id -> this works (though hackish), but doesn't accomplish the join
select r.*, lh.history_id as history_id, latestHistory.* -> appears correct, but results in column name collisions
select r.*, {latestHistory.*} -> error when hibernate looks for a nonexistent column in the result set (this happens if there is any alias at all in the select list)
It doesn't seem to make a lot of difference whether I use addEntity(...) or addJoin(...), as long as the leftmost (root) entity is added using addEntity.
]

I'm thinking you actually need to specify full path for your latestHistory in select e.g.
select {r.*}, {r.latestHistory.*}
otherwise Hibernate gets confused and attempts to treat it as a separate entity. The other option is to not specify injected aliases in select at all which should work for a single "to-one" relationship so long as column order in your tables matches property order in your entities.
I've never tried this on #OneToOne over association table, though.