nullable object must have a value even after "HasValue" check

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I have this LINQ to SQL query:

int? ID = null;
var query = from t in db.things where (!ID.HasValue || t.ID == ID.Value) select t;

Now in regular LINQ this works fine as expected, however in LINQ to SQL is throws a "nullable object must have a value" exception.

Does LINQ to SQL do some weird interpretation of my null check? And if so, how do I implement this functionality correctly?

From what I can see, you're correct Linq to SQL has an issue with this. Based on the answer to this question: Linq to Sql is null in Where clause you want something like this instead.

int? ID = null;
var query = from t in db.things where (!ID.HasValue || (ID.HasValue && t.ID == ID.Value)) select t;

[Solved] Error: Nullable object must have a value, don't write 'nothing' in first line or you can write insert query like below,. Hide Copy Code. "INSERT INTO SIGN(TYPESIGN_ID) VALUES(" +  Nullable object must have a value. at System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource resource) at Microsoft.Exchange.Management.Hybrid.MailFlowTask.ValidateRemoteDomain(DomainContentConfig remoteDomain, Boolean inbound, Boolean OnPrem, Boolean enableSecureMail)

You can do it something like:

int? ID = null;
if(ID.HasValue)
{
   var query = from t in db.things where (t.ID == ID.Value) select t;
}
else //when ID is null
{
   var query = from t in db.things select t;
}

Or it could be done in one line:

var query = ID.HasValue ? from t in db.things where (t.ID == ID.Value)select t : from t in db.things select t;

Nullable object must have a value error in linq SQL C#, Getting "Nullable object must have a value" error in LINQ SQL C#. If you want to show the empty string if a is null, the solution is even simpler:. v-chuncz-msft on: pbix not working after publish yahuang on: Right click menu is not pop up for drill through v-chuncz-msft on: Gateway Connection to CUBE

Ok after using the debugger, turns out that LINQ to SQL doesn't understand the null check and just renders out SQL like this:

SELECT [t0]
FROM [dbo].[things] AS [t0]
WHERE [t0].[ID] = @p0

So when it goes to resolve the value of @p0 it tries to evaluate ID.Value with no regard for my null check.

I solved this issue by using GetValueOrDefault():

int? ID = null;
var query = from t in db.things where (!ID.HasValue || t.ID == ID.GetValueOrDefault()) select t;

In this case it is able to understand the where clause since the variable will always evaluate to some kind of value.

[SOLVED], Use ThenInclude : var workItems = _context.WorkItems .Include(x => x.Contract) .​ThenInclude(contract => contract.ContractAccount);. Experincing issues on creating a custom table, Have the following frown (error) message on executing the code below. Error Message: Nullable Object must have a value.

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Bad error message : "Nullable object must have a value" when , SaveChanges();. But with no indication of which column or even table is causing the problem, or that the problem is at all a missing required field. This means that it may or may not have a value. By casting to DateTime, you are requiring it to have a value. In this case, it does not. Depending on what you're trying to do with it, you may want to check the HasValue property: userRow["LastLogon"] = u.LastLogin.HasValue ? (object) u.LastLogin.ToShortDateString() : DBNull.Value;

Article: "Nullable object must have a value" error is observed after , An error with message "Nullable object must have a value" is observed after upgrading Sitefinity to version 12.0.7025 and above. Any nullable value type is an instance of the generic System.Nullable<T> structure. You can refer to a nullable value type with an underlying type T in any of the following interchangeable forms: Nullable<T> or T?. You typically use a nullable value type when you need to represent the undefined value of an underlying value type.

Comments
  • Did you check if t.ID is null?
  • t.ID is an int so it can't be null - it's also the Primary Key in the DB
  • still t can be null. it looks like ID is an attribute of t
  • Because t comes from the database, it is never null. I have confirmed this using breakpoints also - the exception is definitely coming from the call to ID.Value
  • The change you definition of t.ID to int?. It looks like the database can be null but not your class.
  • Thanks Ben, looked promising but I tried this and got the same error
  • That's not quite right. When ID is null it should select all rows (at least that's how it's written in the question).
  • It should be goes to else { var query = from t in db.things select t}
  • Yeah this is a pretty good solution, the actual query is a bit longer than the example in my question, so there could be a bit of code duplication. However this is definitely an option