public <P> Q leftJoin(Path<? extends Collection<P>> target, Path<P> alias) {
        getMetadata().addJoin(JoinType.LEFTJOIN, createAlias(target, alias));
        return queryMixin.getSelf();
    }
Define a left join from the Collection typed path to the alias

@param <P> type of expression
@param target target of the join
@param alias alias for the join target
@return current object
querydsl-collections/src/main/java/com/querydsl/collections/AbstractCollQuery.java