Null reference in lambda max count

 Public Class Inventory
        Public Property Productcode As String
        Public Property lstattribute As List(Of Attribute)
 End Class
 Public Class Attribute
        Public Property Name As String
        Public Property value As String 
 End Class

I have a list of inventory items. I am trying to get the max count of attributelist in the inventory list

I used this code

oLsInventory.OrderByDescending(Function(c) c.AttributeList.Count).FirstOrDefault().AttributeList.Count

But if my attribute list null. The lambda throws null reference. Is there any way to check for null reference in lambda ? Or is there a better way to rewrite the above开发者_如何学Go linq query ?

Thanks Jothish

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I would place the FirstOrDefault at the very end by adding a Select like so:

oLsInventory.OrderByDescending(Function(c) c.AttributeList.Count).Select(Function(c) c.AttributeList.Count).FirstOrDefault()

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Move FirstOrDefault to the very back and use Select to map your list of Inventories to a list of attribute counts.

 ' Returns 0 if the list is empty
 Dim max = oLsInventory.OrderByDescending(Function(c) c.AttributeList.Count) _
           .Select(Function(c) AttributeList.Count).FirstOrDefault()

Another option is to:

• map the list of inventories to a list of attribute counts
• add Integer.MinValue to the list

• execute Max():

  ' Returns Integer.MinValue if oLsInventory is empty
  Dim maxValue = oLsInventory.Select(Function(c) AttributeList.Count) _
                 .Union(New Integer() {Integer.MinValue}).Max()
  

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This is how I got it working. Before ordering I filtered the null objects..then ran the count on top of that list.

oLsInventory.FindAll(Function(c) c.AttributeList IsNot Nothing).OrderByDescending(Function(c) c.AttributeList.Count).Select(Function(c) c.AttributeList.Count).FirstOrDefault()