/// <summary>
/// Return the number of countries having reported per year for the area filter given
/// </summary>
/// <param name="areaFilter"></param>
/// <returns></returns>
public static IEnumerable <ReportingCountries> GetReportingCountries(AreaFilter areaFilter)
{
DataClassesFacilityDataContext db = getDataContext();
ParameterExpression param = Expression.Parameter(typeof(FACILITYSEARCH_MAINACTIVITY), "s");
Expression exp = LinqExpressionBuilder.GetLinqExpressionArea(areaFilter, param);
// create lambda according to filters
Expression <Func <FACILITYSEARCH_MAINACTIVITY, bool> > lambda = Expression.Lambda <Func <FACILITYSEARCH_MAINACTIVITY, bool> >(exp, param);
IEnumerable <ReportingCountries> years = db.FACILITYSEARCH_MAINACTIVITies.Where(lambda)
.GroupBy(f => f.ReportingYear)
.Select(s => new ReportingCountries(
s.Key,
s.Select(x => x.CountryCode).Distinct().Count()));
return(years);
}