Question

I need select all elements from a set whose Id property is contained within a second set. Can “SelectMany()” be used to accomplish this? What is the most efficient / best solution for this type of matching problem.

Example:
Select all DateRangeIds for a given ReportId by way of a joining entity set.

Sets:

• Reports {ReportId, ReportName}
• ReportDateRanges {DateRangeId, ReportId, ReportDateRangeId}
• DateRanges {DateRangeId, DateRangeName}

Here is my solution’s code. I am unsure if this is the proper approach, but this does solve the problem I’ve described:

    var report = Reports.Take(1).FirstOrDefault();
    int reportId = Convert.ToInt32(report.Id);
    var dateRangeIds = ReportDateRanges.Where(rdr => rdr.ReportId == reportId).OrderBy(it => it.DateRangeId).Select(it => it.DateRangeId);
    var dateRanges = DateRanges.Where(dateRange => dateRangeIds.Contains(dateRange.Id));

LINQ experts, please feel free to critique this code and offer any suggestions. Thanks for the help!

Answer 1

Well, you can use an Enumerable.Intersect(Of TSource) Method (IEnumerable(Of TSource), IEnumerable(Of TSource), IEqualityComparer(Of TSource))

for example:

var list1 = new List<int> {1,2,3,4,5,6,7,8};
var list2 = new List<int> {9,10,11,12,13,4,5};
list1.Intersect(list2);

result

4,5

Using overload specified in link, you can specify EqualityComparer for your custom object in order to find intersection of both enumerations.

Hope this helps.