Conversion/comparison of different numeric types inside streams

Question

I'm having a problem with Stream API... again. The functionality I'm trying to implement isn't the hardest thing, but I'm having difficulties filtering since there are incompatible types and I don't how to make the comparison right. The idea is to get information about departments which the given sections are linked to.

department.getSectionId() returns Long while Section::getId is an Integer (which I can't change)

private List<DepartmentInfo> retrieveLinkedDepartments(final Collection<Section> sections) {
        return this.departmentDao
                .findAll()
                .stream()
                .filter(department -> department.getSectionId() != null)
                .filter(department -> department.getSectionId().equals(sections.stream().map(Section::getId)))                                           
                .map(this.departmentInfoMapper::map)
                .collect(Collectors.toList());
}

Of course the result of the main predicate is always false. I know the code is awful and I'm not defining conditions right, but I hope you get the idea. Maybe there's a possibility to somehow merge these collections or compare in a smart way.

Thank you in advance!

Answer 1

As of now you are comparing a Long and a Steam<Integer> which will always return false.

You can flip around your logic a little and use a mapToLong to convert the int's to Long's:

private List<DepartmentInfo> retrieveLinkedDepartments(final Collection<Section> sections) {
    return this.departmentDao
               .findAll()
               .stream()
               .filter(department -> department.getSectionId() != null)
               .filter(department -> sections.stream()
                                 .mapToLong(Section::getId)                                     
                                 .anyMatch(department.getSectionId()::equals))                                           
               .map(this.departmentInfoMapper::map)
               .collect(Collectors.toList());
}

This will convert Section::getId to a Stream<Long>, and then filter through the Stream to see if any of the department.getSectionId equals the Id.