Linq - Select a single child collection item

.net entity-framework linq vb.net

Question

I have a parent child collection objects and was wondering how to get a single item from the child collection using Linq

Parent Collection

Public Class FaultCodeModel

    Public Property ID As Short
    Public Property Description As String
    Public Property FaultCodeDetails As List(Of FaultCodeDetailModel)

End Class

Child Collection 

Public Class FaultCodeDetailModel

    Public Property ID As Short
    Public Property Description As String
    Public Property NotifyPurchasing As Boolean
    Public Property NotifyPurchasingAfterHits As Short
    Public Property NotifyExpediting As Boolean
    Public Property NotifyExpeditingAfterHits As Short
    Public Property NotifyBuyer As Boolean
    Public Property NotifyBuyerAfterHits As Short
    Public Property NotifySupplier As Boolean
    Public Property NotifySupplierAfterHits As Short
    Public Property NotiifyProPack As Boolean
    Public Property NotiifyProPackAfterHits As Short
    Public Property NotifyGoodsInTeamLeader As Boolean
    Public Property NotifyGoodsInTeamLeaderAfterHits As Short

End Class

I have tried the below Linq query but it is returning multiple child items where the parent ID field is matched.

Dim var = From fcd In FaultCodes Where fcd.FaultCodeDetails.Any(Function(w) w.ID.Equals(faultCodeDetailID))
            Select fcd.FaultCodeDetails

How do I get a single item from the child collection?

1
2
1/12/2012 11:43:57 AM

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Accepted Answer

Dim fcdID = 4711
Dim fcdm = (From fc In FaultCodes
           From fcd In fc.FaultCodeDetails
           Where fcd.ID = fcdID
        Select fcd).FirstOrDefault

http://msdn.microsoft.com/en-us/library/bb340482.aspx

4
1/12/2012 11:57:45 AM

Popular Answer

I think you want to have this:

FaultCodes.SelectMany(Function(w) w.FaultCodeDetails)
          .Where(Function(w) w.ID.Equals(faultCodeDetailID))

This returns all the child items whose ID equals faultCodeDetailID.

(I am a C# guy, maybe the VB.NET syntax is a bit off. Please correct it yourself)

C# version:

FaultCodes.SelectMany(x => x.FaultCodeDetails)
          .Where(x => x.ID == faultCodeDetailID)
Daniel Hilgarth

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