MVVM: where is the best place to integrate an id counter, in ViewModel or Repository or... ?
- by msfanboy
Hello,
I am using http://loungerepo.codeplex.com/
this library needs a unique id when I persist my entities to the repository.
I decided for integer not Guid.
The question is now where do I retrieve a new integer and how do I do it?
This is my current approach in the SchoolclassAdministrationViewModel.cs:
public SchoolclassAdministrationViewModel()
{
_schoolclassRepo = new SchoolclassRepository();
_pupilRepo = new PupilRepository();
_subjectRepo = new SubjectRepository();
_currentSchoolclass = new SchoolclassModel();
_currentPupil = new PupilModel();
_currentSubject = new SubjectModel();
...
}
private void AddSchoolclass()
{
// get the last free id for a schoolclass entity
_currentSchoolclass.SchoolclassID = _schoolclassRepo.LastID;
// add the new schoolclass entity to the repository
_schoolclassRepo.Add(SchoolclassModel.SchoolclassModelToSchoolclass(_currentSchoolclass));
// add the new schoolclass entity to the ObservableCollection bound to the View
Schoolclasses.Add(_currentSchoolclass);
// Create a new schoolclass entity and the bound UI controls content gets cleaned
CurrentSchoolclass = new SchoolclassModel();
}
public class SchoolclassRepository : IRepository<Schoolclass>
{
private int _lastID;
public SchoolclassRepository()
{
_lastID = FetchLastId();
}
public void Add(Schoolclass entity)
{
//repo.Store(entity);
}
private int FetchLastId()
{
return // repo.GetIDOfLastEntryAndDoInc++
}
public int LastID
{
get { return _lastID; }
}
}
Explanation: Every time the user switches to the SchoolclassAdministrationViewModel which is datatemplated with a UserControl the saVM Ctor is called and the schoolclass repository is created wherein the FetchLastId() is called and I am up to date with the last ID doing a inc++ on it to get the free one...
Do you have any better ideas?
What I do not like about my current apporach:
-Having a private method in repositry class because a repositry is to fetch data only not "entity logic" like the counter
- Having to access from the ViewModel a public property - located in the repository -, actually its not the ViewModel concern to get a entity id and assign it. Actually the ViewModel should ask for a schoolclass POCO and get a SchoolclassModel to bind to the UI. But then I have again to re-read the Schoolclass properties into the SchoolclassModel properties what I want to avoid.
