Question

The title doesn’t tell the complete story. Please read the message.

I have two objects: Adult and Child. Child has a boolean field isMale, and a reference to Adult. Adult doesn’t reference Child.

public class Adult {
   long id;
}
public class Child {
   long id;
   boolean isMale;
   Adult parent;
}

I want to create a query to list the number of sons each adult has including adults who don’t have any sons. I tried:

Query 1

SELECT adult, COUNT(child) FROM Child child 
RIGHT OUTER JOIN child.parent as adult 
WHERE child.isMale='true' 
GROUP BY adult

which translates to sql

select
    adult.id as col_0_0_,
    count(child.id) as col_1_0_,
    ... {omit properties}
from
    Child child
right outer join
    Adult adult
        on child.parentId=adult.id 
where
    child.isMale = 'true'
group by
    adult.id

Query 1 doesn’t pick up adults that don’t have any sons.

Query 2:

SELECT adult, COUNT(child.isMale) FROM Child child 
RIGHT OUTER JOIN child.parent as adult 
GROUP BY adult

translates to sql:

select
    adult.id as col_0_0_,
    count(child.id) as col_1_0_,
    ... {omit properties}
from
    Child child
right outer join
    Adult adult
        on child.parentId=adult.id 
group by
    adult.id

Query 2 doesn’t have the right count of sons. Basically COUNT doesn’t evaluate isMale.
The where clause in Query 1 filtered out Adults with no sons.

How do I build a HQL or a Criteria query for this use case?

Thanks.

Answer 1

Condition child.isMale='true' is false for adults without children (isMale is NULL), therefore you should handle this case:

SELECT adult, COUNT(child) 
FROM Child child RIGHT OUTER JOIN child.parent as adult 
WHERE child IS NULL OR child.isMale='true'  
GROUP BY adult