Get record with max id, using Hibernate Criteria

Question

Using Hibernate\'s Criteria API, I want to select the record within a table with the maximum value for a given column.

I tried to use Projections, creating an alias

Answer 1

    Date maxDateFromDB = null;
    Session session = (Session) entityManager.getDelegate();
//Register is and Entity and assume maxDateFromDB is a column.
//Status is another entity with Enum Applied.
//Code is the Parameter for One to One Relation between Register and Profile entity.
    Criteria criteria = session.createCriteria(Register.class).setProjection(Projections.max("maxDateFromDB") )
    .add(Restrictions.eq("status.id", Status.Name.APPLIED.instance().getId()));
    if(code != null && code > 0) {
        criteria.add(Restrictions.eq("profile.id", code));
    }
    List<Date> list = criteria.list();

    if(!CollectionUtils.isEmpty(list)){
        maxDateFromDB = list.get(0);
    }

Answer 2

For the max() function in hibernate:

criteria.setProjection(Projections.max("e.encounterId"));

Answer 3

You can use a DetachedCriteria to express a subquery, something like this:

DetachedCriteria maxId = DetachedCriteria.forClass(Foo.class)
    .setProjection( Projections.max("id") );
session.createCriteria(Foo.class)
    .add( Property.forName("id").eq(maxId) )
    .list();

References

• Hibernate Core Reference Guide
  • 15.8. Detached queries and subqueries

Answer 4

I found that using addOrder and setMaxResults together worked for me.

Criteria c = session.createCriteria(Thingy.class);
c.addOrder(Order.desc("id"));
c.setMaxResults(1);
return (Thingy)c.uniqueResult();

Using the MySQL dialect, this generates a SQL prepared statement about like this (snipping out some of the fields):

select this_.id ... from Thingy this_ order by this_.id desc limit ?

I am not sure if this solution would be effective for dialects other than MySQL.

Answer 5

Use

addOrder(Order.desc("id"))

and fetch just the first result :)

Answer 6

HQL:

from Person where person.id = (select max(id) from Person)

Untested. Your database needs to understand subselects in the where clause.

Too lazy to find out if/how such a subselect can be expressed with the criteria api. Of course, you could do two queries: First fetch the max id, then the entity with that id.