@Override
    public List<T> fetch() {
        @SuppressWarnings("unchecked") // This is the built type
        Expression<T> projection = (Expression<T>) queryMixin.getMetadata().getProjection();
        return queryEngine.list(getMetadata(), iterables, projection);
    }
Define a left join from the Map typed path to the alias

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