NullReferencException in DLinq lambda method

  • Thread starter Thread starter Andrus
  • Start date Start date
A

Andrus

I tried DLinq code created by Marc and got NRE in ToList() line.
Any idea what causes this ?

Andrus.

Code:

Northwind db = CreateDB();
var orders = db.GetTable<Order>().ToArray().AsQueryable();

var query = from order in orders
select new
{
OrderID = order.OrderID,
Customer = new
{
ContactName = order.Customer.ContactName,
ContactTitle = order.Customer.ContactTitle
}
};
var list = query.ToList();

result:

System.NullReferenceException was unhandled
Message="Object reference not set to an instance of an object."
Source="Anonymously Hosted DynamicMethods Assembly"
StackTrace:
at lambda_method(ExecutionScope , Order )
at System.Linq.Enumerable.<SelectIterator>d__d`2.MoveNext()
at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)

....
 
I tried DLinq code created by Marc and got NRE in ToList() line.
Any idea what causes this ?
Click to expand...

I suggest you find the query it's generated and look at the results.
Look for an order which doesn't have a customer, and check that the
query actually picks up the customer information to start with.

Jon
 
Jon's answer looks about right... as a quick check, try adding:

where order.Customer != null

between the "from" and "select"; if it goes away, that is the problem.

Marc
 
Jon's answer looks about right... as a quick check, try adding:
where order.Customer != null

between the "from" and "select"; if it goes away, that is the problem.
Click to expand...

I added this check and NRE disappears.
However query does not return any rows in this case.
Is this expected result from this query ?
Should it work without where clause also ?

Andrus.
 
Andrus said:
I added this check and NRE disappears.
However query does not return any rows in this case.
Is this expected result from this query ?
Should it work without where clause also ?
Click to expand...

Have you looked at the generated SQL?
 
Andrus said:
I tried DLinq code created by Marc and got NRE in ToList() line.
Any idea what causes this ?

Andrus.

Code:

Northwind db = CreateDB();
var orders = db.GetTable<Order>().ToArray().AsQueryable();

var query = from order in orders
select new {
OrderID = order.OrderID,
Customer = new {
ContactName = order.Customer.ContactName,
ContactTitle = order.Customer.ContactTitle
}
};
var list = query.ToList();

result:

System.NullReferenceException was unhandled
Message="Object reference not set to an instance of an object."
Source="Anonymously Hosted DynamicMethods Assembly"
StackTrace:
at lambda_method(ExecutionScope , Order )
at System.Linq.Enumerable.<SelectIterator>d__d`2.MoveNext()
at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
Click to expand...

ToList() enumerates the list, so it will crash if order.Customer is null.

FB

--
------------------------------------------------------------------------
Lead developer of LLBLGen Pro, the productive O/R mapper for .NET
LLBLGen Pro website: http://www.llblgen.com
My .NET blog: http://weblogs.asp.net/fbouma
Microsoft MVP (C#)
------------------------------------------------------------------------
 
ToList() enumerates the list, so it will crash if order.Customer is null.

new operator in query creates new object. so order.Customer *cannot* be
null.

Andrus.
 
new operator in query creates new object. so order.Customer *cannot*
be null.
Click to expand...

No - the "new Customer" in the query posted only applies to the
anonymous type you are generating. It says nothing at all about whether
order.Customer is null or not.

Try simply enumerating the orders, and listing what Customer is...

Marc
 
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