Tricky LINQ and nested collection - linq

Question

I am trying to figure out an easier way I can take the following code and condense it into as few lines as possible. Ideally, I would like to get an IDictionary> out of this.
var report = db.Reports.Select(rid => rid.ID == reportId) as Report;
Dictionary<string, List<string>> notes = new Dictionary<string, List<string>>();
foreach (var subreport in report.SubReports)
{
foreach (var subreportitem in subreport.SubReportItems)
{
notes[subreportitem.Title] = new List<string>();
foreach (var note in subreportitem.SubReportItemNotes)
{
notes[subreportitem.Title].Add(note.NoteDetails);
}
}
}
Ideally, I had wanted to do something like so:
from report in db.Reports
where report.ID == reportId
from subreports in report.SubReports
from subreportitems in subreports.SubReportItems
from notes in subreportitems.SubReportItemNotes
//Unsure how to select into the desired dictionary...

Answer 1

This should be equivalent:
db.Reports
.Where(rpt => rpt.ID == reportId)
.Cast<Report>()
.SelectMany(rpt => rpt.SubReports)
.SelectMany(subRpt => subRpt.SubReportItems)
.ToDictionary(
sri => sri.Title,
sri => sri.SubReportItemNotes.SelectMany(note => note.NoteDetails);
Notes:
The first line of your code uses .Select(rid => rid.Id == reportId), but I assumed this should have been Where instead of Select, otherwise you would end up with a collection of null because the Select results would be of type bool and the as Report would output null for each.
This only works if the Titles of all of your SubReportItems are unique. It is conceivable that one Report could have 10 SubReports and that among those SubReports there are two or more SubReportItems with the same Title. If that is the case, then you may need to rethink this a bit, otherwise you will get a DuplicateKeyException when you try to add a Title that is already in the dictionary.
Explanation:
Basically, we are taking the set of reports, and applying the condition that we only want reports where the ID is the desired one. Personally, I would put this in a separate line, and use SingleOrDefault instead of Where because I expect only one result.
Next, we call .Cast<Report> just because you are using as Report, so I guess you had a need for it. This may be redundant and unnecessary in practice.
The first .SelectMany call will get all SubReports of all Reports. Again, we probably will only ever have one Report object at this point.
Now we have a bunch of SubReports, but we really want to get all the SubReportItems, so we use another SelectMany to get those.
Now that we have all the SubReportItems from all the SubReports from all the (1) Reports, we create the dictionary. For each SubReportItem we create a key from the Title property, and then for the value we use one final SelectMany to get all the NoteDetails objects associated with all the current SubReportItemNotes.