C# Linq Select Many

Question

Hi All I am matching Cases to Controls basically records in the Case list need to have the number of matches that is specified in the string 'm_ctrlno'. So far i have two lists the where clause is correct however i'm unsure how to use SelectMany to get the 3 Controls that match 1 Case. I decided to use the .Take() function however it doesn't seem to be working. I'm not getting the same case with 3 different controls when i cycle on the var query. Any ideas? Many thanks J. Here is the code: List CurrentCaseList = new List (); foreach (CaseSelection CurrentCase in m_casesarraylist) CurrentCaseList.Add(CurrentCase); List CurrentControlList = new List (); foreach (ControlSelection CurrentControlRec in ControlList) CurrentControlList.Add(CurrentControlRec); var query = CurrentCaseList.SelectMany( c => CurrentControlList.Where(o => o.pracid == c.pracid && o.sex == c.sex && CaseSelectionList.AgeIsInRange(c.yob o.yob m_years)) (c o) => new { o c }).Take(m_ctrlno);

Aarti · Answer

In your code You define 2 list CurrentCaseListCurrentControlList but not define CaseSelectionList. to get the 3 controls that matches one case for this see below code: the SelectMany method to select all orders where TotalDue is less than 500.00. decimal totalDue = 500.00M; using (AdventureWorksEntities context = new AdventureWorksEntities()) { ObjectSet contacts = context.Contacts; ObjectSet orders = context.SalesOrderHeaders; var query = contacts.SelectMany( contact => orders.Where(order => (contact.ContactID == order.Contact.ContactID) && order.TotalDue .Select(order => new { ContactID = contact.ContactID LastName = contact.LastName FirstName = contact.FirstName OrderID = order.SalesOrderID Total = order.TotalDue })); foreach ( var smallOrder in query) { Console.WriteLine( Contact ID: {0} Name: {1} {2} Order ID: {3} Total Due: ${4}   smallOrder.ContactID smallOrder.LastName smallOrder.FirstName smallOrder.OrderID smallOrder.Total); } }

Jacques Sandler · Answer

Thanks very much that is actually very useful. I modified it a little bit and there is the result which actually works if anyone is interested. Many thanks J List CurrentCaseList = new List (); foreach (CaseSelection CurrentCase in m_casesarraylist) CurrentCaseList.Add(CurrentCase); List CurrentControlList = new List (); foreach (ControlSelection CurrentControlRec in ControlList) CurrentControlList.Add(CurrentControlRec); var q2 = CurrentCaseList.SelectMany( c => CurrentControlList.Where(o => o.pracid == c.pracid && o.sex == c.sex && CaseSelectionList.AgeIsInRange(c.yob o.yob m_years)) .Select(o => new { CasePat = c.patid CasePrac = c.pracid ContPat = o.patid ContPrac = o.pracid }).Take(m_ctrlno));

Jacques Sandler · Answer

Ok so after some more debugging it seems that the code above gives part of the correct result. e.g. if 'm_ctrlno' is equal to 2 (So 2 Controls to a Case) I get: Case Patient 0001 Control Patient 0004 Case Patient 0001 Control Patient 0005 Which is correct as the records fill the correct criteria. However it should do this for the whole Case list not just one patient. So i need to get the same as above for all the Case Patients and their Control matches. Any ideas?