Predicate

    private bool PartsFilter(Object item)
    {
        var editPartViewModel = item as EditPartViewModel;
        return PartsSearchFilter(editPartViewModel) &&
               PartsWithErrorFilter(editPartViewModel);
    }

    private bool PartsSearchFilter(EditPartViewModel editPartViewModel)
    {
        return editPartViewModel.PartName.ToUpper().Contains(_searchFilterString.ToUpper());
    }

    private bool PartsWithErrorFilter(EditPartViewModel editPartViewModel)
    {
        return _errorParts ? editPartViewModel.HasErrors : true;
    }