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15.16. Tips & Tricks

You can count the number of query results without returning them: 
( (Integer) session.createQuery("select count(*) from ....").iterate().next() ).intValue()
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To order a result by the size of a collection, use the following query: 
select usr.id, usr.name
from User as usr
    left join usr.messages as msg
group by usr.id, usr.name
order by count(msg)
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If your database supports subselects, you can place a condition upon selection size in the where clause of your query: 
from User usr where size(usr.messages) >= 1
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If your database does not support subselects, use the following query: 
select usr.id, usr.name
from User usr
    join usr.messages msg
group by usr.id, usr.name
having count(msg) >= 1
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As this solution cannot return a User with zero messages because of the inner join, the following form is also useful: 
select usr.id, usr.name
from User as usr
    left join usr.messages as msg
group by usr.id, usr.name
having count(msg) = 0
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Properties of a JavaBean can be bound to named query parameters: 
Query q = s.createQuery("from foo Foo as foo where foo.name=:name and foo.size=:size");
q.setProperties(fooBean); // fooBean has getName() and getSize()
List foos = q.list();
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Collections are pageable by using the Query interface with a filter: 
Query q = s.createFilter( collection, "" ); // the trivial filter
q.setMaxResults(PAGE_SIZE);
q.setFirstResult(PAGE_SIZE * pageNumber);
List page = q.list();
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Collection elements can be ordered or grouped using a query filter: 
Collection orderedCollection = s.createFilter( collection, "order by this.amount" ).list();
  Collection counts = s.createFilter( collection, "select this.type, count(this) group by this.type" ).list();
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You can find the size of a collection without initializing it: 
( (Integer) session.createQuery("select count(*) from ....").iterate().next() ).intValue();
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