Develop Reference

How to properly Select DTO projections using JPA Join tables?

I have one entity and a one to one relationship. Now i'm looking for the best way to retrieve specific fields from both tables using a projection.
In my first attempt i've tried:
"SELECT NEW br.com.domain.order.Order( " +
"o.id," +
"o.description," +
"p.payment) " +
"FROM Order o
Using this way i have a single constructor inside Order entity, to retrieve only these 3 fields. But now i have N+1 queries.
The second option is the follow:
"SELECT NEW br.com.domain.order.OrderDTO( " +
"o.id," +
"o.description," +
"p.status,
p.locationId,
p.value) " +
"FROM Order o JOIN o.payment p
This works great but i have to create a DTO class.
How can i do something like this:
"SELECT NEW br.com.domain.order.Order( " +
"o.id," +
"o.description," +
"p.status,"+
"p.locationId,"+
"p.value)"
It's necessary to create a constructor inside both entities to load all properties?

sql to hql throwing exception

I'm using hibernate in my project and I'm trying to convert an existing sql query from DaoImplementation class to hql,
The sql query I have is
JdbcTemplate select = new JdbcTemplate(dataSource);
String sql = "SELECT * FROM (SELECT site_id,rtc,sigplan,cycle_time,health,phase_no,phase_time,active_groups,groupscolour,ip "+
"FROM status_data where rtc>='" + fromDate + "' and rtc<'" + toDate + "' and "+
"site_id=" + SiteId + " order by rtc desc limit "+recordLimit+" )as temp ORDER BY RTC ASC";
I wrote the hql version to get data from HealthLog table as
String hql = " select f from (select h from HealthLog h where rtc>='"+fromDate+"' and rtc <'"+toDate+"' "
+ "and siteId = "+siteId+" order by rtc desc limit "+limit+" ) as f order by rtc asc ";
return super.readListByHql(hql);
But the above hql throws the following exception
org.hibernate.hql.internal.ast.QuerySyntaxException: unexpected token: ( near line 1, column 16 [ select f from (select h from com.traff.hibernate.model.HealthLog as h where rtc>='1974-08-01 14:10:00.0' and rtc <'1974-09-01 23:46:20.6' and siteId = 20 order by rtc desc limit 50000 ) as f order by rtc asc ]
at org.hibernate.hql.internal.ast.QuerySyntaxException.convert(QuerySyntaxException.java:54)
at org.hibernate.hql.internal.ast.QuerySyntaxException.convert(QuerySyntaxException.java:47)
at org.hibernate.hql.internal.ast.ErrorCounter.throwQueryException(ErrorCounter.java:79)
at org.hibernate.hql.internal.ast.QueryTranslatorImpl.parse(QueryTranslatorImpl.java:276)
at org.hibernate.hql.internal.ast.QueryTranslatorImpl.doCompile(QueryTranslatorImpl.java:180)
at org.hibernate.hql.intern
I also tried the below code snippet but that giving me wrong results
Criteria criteria = createEntityCriteria();
criteria.add(Restrictions.ge("rtc", fromDate));
criteria.add(Restrictions.lt("rtc", toDate));
criteria.add(Restrictions.eq("siteId", siteId));
criteria.setMaxResults(limit);
criteria.addOrder(Order.asc("rtc"));
criteria2 = criteria;
criteria2.addOrder(Order.desc("rtc"));
return criteria2.list();
Which is the correct way to achieve the result?

First of all, as already mentioned in the comments, you cannot do a subquery within the FROM clause in HQL.
See: Hibernate Documentation
Secondly, the limit keyword is not supported by HQL.
Usually you would use query.setFirstResult(0) and query.setMaxResults(recordLimit) methods where query has the type of the Query Interface. But since you are using the limit in a subquery, there is no way.
See: How to set a limit to inner query in Hibernate?
Some options:
Use a native SQLQuery
Since you are only sorting in the outer Query. You could only execute the inner query and sort in Java.
Example for Option 2:
Session session = factory.openSession();
Query query = session
.createQuery("FROM HealthLog "
+ "WHERE rtc >= :rtcL and rtc < :rtcG and siteId = :siteId "
+ "ORDER BY rtc DESC");
query.setParameter("rtcL", fromDate);
query.setParameter("rtcG", toDate);
query.setParameter("siteId", siteId);
query.setFirstResult(0);
query.setMaxResults(recordLimit);
List<HealthLog> res = query.list();
session.close();
Collections.sort(res, new Comparator<HealthLog>() {
public int compare(HealthLog o1, HealthLog o2) {
return o1.getRtc().compareTo(o2.getRtc());
}
});
The query above returns HealthLogs with all attributes. If you want to only retrieve specific attributes, you can add a SELECT new HealthLog(siteId,rtc,sigplan,cycle_time,...) to your Query with a fitting constructor in HealthLog.
Please note that the code snippet might not be ready to use, since i do not know your model and attribute names.

How do I write join in Ebean Java ORM language

Currently my code is
int customerId = 4;
String sql = "select id from coupon as A join coupon_use "
+ "as B on A.id=B.coupon where B.customer=" + customerId
+ " and B.like_at is not null;";
RawSql rawSql = RawSqlBuilder.parse(sql).create();
Query<Coupon> query = Ebean.find(Coupon.class);
query.setRawSql(rawSql);
List<Coupon> list = query.findList();
return ok(Json.toJson(list));
How do I avoid writing manual sql query but still have the ORM generate that query and return me the result?

Ebean will add appropriate joins based on the paths/properties used in the where and order by etc.
where couponUse.likeAt is not null.
Assuming couponUse.likeAt is the correct expression path ... Ebean will add a join to support the expression automatically.

Setting ORDER BY and LIMIT clause on JPA Query

I'm very, very new to Hibernate and JPA. I want to be able to apply ORDER BY and LIMIT clauses to a Hibernate(?) query, but am coming up empty. NOTE: I inherited this code.
Here is the current code:
public SomeCoolResponse getSomeCoolResponse(String myId) {
String queryString = "select aThing from AWholeBunchOfThings aThing " +
"join aThing.thisOtherThing oThing join oThing.StillAnotherThing saThing " +
"where saThing.subthing.id = :id";
Query q = getEntityManager().createQuery(queryString);
q.setParameter("id", myId);
List<MyThings> list = q.getResultList();
if(list.size() > 0) {
return list.get(0);
}
return null;
}
Instead of getting an entire list and then just returning the first result (which is the only one we need), I'd like to be able to apply a LIMIT 0,1 clause so that the query will be faster. Also, the query needs to be sorted descending on aThing.created which is a UNIX timestamp integer.
I've tried altering queryString like this:
String queryString = "select aThing from AWholeBunchOfThings aThing " +
"join aThing.thisOtherThing oThing join oThing.StillAnotherThing saThing " +
"where saThing.subthing.id = :id ORDER BY aThing.created LIMIT 0,1";
But Hibernate still returns the entire set.
I've looked at using the JPA CriteriaBuilder API, but it hurt my brain.
I'm a total n00b when it comes to this, and any help is greatly appreciated!

I think you need
q.setMaxResults(1);
See also the accepted answer here.
How do you do a limit query in HQL?
As to the "order by" clause you may include it in the queryString.

The JPQL equivalent to LIMIT start,max is:
setFirstResult and setMaxResults:
q.setFirstResult(start);
q.setMaxResults(limit);

More elegant way to write a hibernate query

Can someone help me write a better code. I tried this but its not working :
Query query = session.createQuery("from MyTable order by :sortvariable :sortorder");
query.setParameter("sortvariable", sortvar);
query.setParameter("sortorder", order);
This is not working as well
Query query = session.createQuery("from MyTable table order by table." + sortvar + " " + " :sortorder");
query.setParameter("sortorder", order);
I managet to get it working with this :
Query query = session.createQuery("from MyTable table order by table." + sortvar + " " + order);
I need to do this with query because I'm using setMaxResults() and setFirstResult().

I don't think you can use parameters to identify keywords that way. Is it possible to do what you're trying to do using the criteria API?
boolean sortAscending = ...;
Criteria criteria = session.createCriteria(MyTable.class);
criteria.addOrder(sortAscending? Order.asc(sortVar): Order.desc(sortVar));