Re: Outer join with ConstructorExpression

[Timo Westkämper]

Hi.

You can't enforce a left join at this level in Querydsl. To get a left join you need to left join explcitly in the query construction like this :

query.from(category)
        .leftJoin(category.parent, parent)
        .list(new ConstructorExpression(someClass, category.name, parent))

Br,
TImo

On Sat, Oct 20, 2012 at 1:34 PM, Querydsl on behalf of Jose Miguel Samper <querydsl+noreply-APn2wQf7_6Utszs...@googlegroups.com> wrote:

I'm using ConstructorExpression.create programmatically to generate constructor projections as explained in the reference documentation, section 3.1.4.

My main JPA Entity is

   @Entity
   public class Category {
        ...
        private String name;

        @ManyToOne
        private Category parent;
        ...
    }

When a constructor argument is a JPA relationship (the "parent" field), the generated SQL uses an INNER JOIN, but I need a LEFT JOIN, as the field could be NULL.

Is there any way to force a LEFT JOIN instead of an INNER JOIN?

With JPA CriteriaBuilder it is acomplished as in the following example (look at "parent" argument):

   ...
   root = query.from(Category.class);
   CompoundSelection constructor = criteriaBuilder.construct(MyProjection.class,

      root.get("name") 
      root.join("parent", JoinType.LEFT));
   query.select(constructor);

   ...

Regards,
    Jose Samper

--
Timo Westkämper
Mysema Oy
+358 (0)40 591 2172
www.mysema.com

[Jose Miguel Samper]

Ok, that worked like a charm.

Thanks for the quick answer.