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c#linqlinq-to-sql
Chris
Chris

Reputation: 7611

Nullable object must have a value - why?

I have the following LINQ query

from p in dc.Purchases
where invoiceNumber == null || p.InvNumber == invoiceNumber.Value
select p;

The 'invoiceNumber' is a nullable int - when it's null, the program throws a 'Nullable object must have a value error'. Why is this when it's explicitly checking if it's null first? Is there a way around this?

Thanks,

Upvotes: 5

Views: 12647

Answers (9)

RePierre
RePierre

Reputation: 9566

I think there is something wrong with your query. From the code you've supplied I assume that invoiceNumber is a local variable or a parameter. If this is the case, then why are you even checking if invoiceNumber == null in your query? Such check should be done separately from the query:

if(invoiceNumber == null)
{
    return dc.Purchases; 
    // the query would evaluate to this because invoiceNumber == null will allways return true.
}
else
{
    return 
        from p in dc.Purchases 
        where p.InvNumber == invoiceNumber.Value
        select p;
}

Upvotes: 2

Naga Sandeep
Naga Sandeep

Reputation: 1431

The basic concept of nullable type is... the underlying type will have all the values specified in its range + a null value, to increase the flexibility with the database programming.

nullable types has two readonly properties 1) HasValue 2) Value

HasValue is boolean type and it is set to true automatically if Value has some value in it. So, for comparisions, you have to use HasValue first and then Value. If u use Value directly, and if it is null, then the above exception will be thrown.

keeping these in mind, I doubt this fragment too,. where invoiceNumber == null you should try invoiceNumber.Value==null (not invoiceNumber)

or

where invoiceNumber.HasValue && p.InvNumber == invoiceNumber.Value

thanks

Upvotes: 0

Ash
Ash

Reputation: 1984

The problem can be in Linq-to-Sql - it's trying to convert where statement to SQL so invoiceNumber.Value can be called even it's null.

Please just try where invoiceNumber == null || p.InvNumber == invoiceNumber.

Hope it'll help.

Upvotes: 0

userGS
userGS

Reputation: 220

you don't need to check for null explicitly. there might two cases with the nullable values either it will be null or has some value.

e.g.

CASE 1-

 int ? invoiceNumber = null;
 var prods = from p in dc.Purchases 
             where p.InvNumber == invoiceNumber
             select p;

CASE 2- 

 int ? invoiceNumber = 100;
 var prods = from p in dc.Purchases 
             where p.InvNumber == invoiceNumber
             select p;

same linq statement will work in both the cases.

Upvotes: 0

voidengine
voidengine

Reputation: 2579

You don't tell, but I suspect that p.InvNumber is nullable as well. In that case, don't use the .Value:

from p in dc.Purchases
where invoiceNumber == null || p.InvNumber == invoiceNumber
select p;

Upvotes: 0

2GDev
2GDev

Reputation: 2466

Use the HasValue property to check if a Nullable has value.

from p in dc.Purchases
where !invoiceNumber.HasValue || p.InvNumber == invoiceNumber.Value
select p;

Upvotes: 0

Jodrell
Jodrell

Reputation: 35716

what about

from p in dc.Purchases 
where (invoiceNumber ?? p.InvNumber) == p.InvNumber
select p;

but, I would pose the question, if invoiceNumber is null why run this statement?

Upvotes: 0

Likurg
Likurg

Reputation: 2760

Check this one

from p in dc.Purchases
where (invoiceNumber == null ? p.InvNumber == null : p.InvNumber == invoiceNumber.Value)
select p;

Upvotes: 0

Zaheer Ahmed
Zaheer Ahmed

Reputation: 28528

try this:

from p in dc.Purchases
where invoiceNumber == null ||(invoiceNumber!=null && p.InvNumber == invoiceNumber.Value)
select p;

Upvotes: 0

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