Error: Nullable object must have a value

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SQL-Server-2005

VB

SQL-Server

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I want to enter data NULL (rather than numeric numbers, etc.) to the field of type integer. I use the following code:

VB

Dim Col2 As Nullable(Of Integer) = Nothing
OpenDatabase()
Command.Connection = Con
Command.CommandType = CommandType.Text
Command.CommandText = "INSERT INTO SIGN(TYPESIGN_ID) VALUES('" + CStr(Col2) + "')"
Command.ExecuteNonQuery()
Con.Close()

the result is "Nullable object must have a value". where my mistake?
Note : I'm using VB .Net 2010 & sql server 2005

Posted 28-Aug-12 16:37pm

om3n

Updated 12-Oct-19 16:52pm

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3 solutions

Solution 1

If this is a nullable object, you don't need to use CStr.
Or else check if Col2 is not null before using CStr.

Posted 28-Aug-12 16:59pm

Abhinav S

Comments

om3n 28-Aug-12 23:14pm

I've tried as you say:
Command.CommandText = "INSERT INTO SIGN(TYPESIGN_ID) VALUES('" + Col2 + "')"
I get error "Conversion from string"')" to type 'Double' is not valid."

I'm also try :
Command.CommandText = "INSERT INTO SIGN(TYPESIGN_ID) VALUES('" + Col2.ToString + "')"
Also get error "The INSERT statement conflicted with the FOREIGN KEY constraint "FK_SIGN_TYPE_SIGN". The conflict occurred in database "database", table "dbo.TYPE_SIGN", coloumn 'TYPESIGN_ID'. The statement has been terminated."

if using Col2.ToString the value is 0

Abhinav S 28-Aug-12 23:23pm

If this is a foreign key, it can only have values from within the primary key. If you try to set it to null or 0, you are going to get errors. Use it only with the proper values.

om3n 28-Aug-12 23:55pm

thanks Abhinav S,
understood, but I need enter NULL value not 0 either numeric or alphabetic,
I tried directly to sql server database, there is can accept null values

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Aarti Meswania · Accepted Answer · 2012-08-28T17:00:00

Solution 2

don't write 'nothing' in first line
or
you can write insert query like below,

"INSERT INTO SIGN(TYPESIGN_ID) VALUES(" + "null" + ")"

Happy Coding!
:)

Posted 28-Aug-12 17:00pm

Aarti Meswania

Comments

om3n 28-Aug-12 23:39pm

thanks all,
I've tried :

Dim Col2 As Nullable(Of Integer)
OpenDatabase()
Command.Connection = Con
Command.CommandType = CommandType.Text
Command.CommandText = "INSERT INTO SIGN(TYPESIGN_ID) VALUES('" + Col2 + "')"
Command.ExecuteNonQuery()
Con.Close()
Still can't, I get error "Conversion from string"')" to type 'Double' is not valid."

if using :
"INSERT INTO SIGN(TYPESIGN_ID) VALUES(" + "null" + ")"
the result is successfully.

however, what if insert null values using variables?

Aarti Meswania 29-Aug-12 0:27am

welcome :)

Ganesh Nikam · Accepted Answer · 2012-08-28T19:07:00

hiii,

SQL

To retrieve the value of a variable of a nullable type, you should first test its HasValue property to confirm that it has a value. If you try to read the value when HasValue is False, Visual Basic throws an InvalidOperationException exception. The following example shows the recommended way to read the variable Col2

If Col2.HasValue Then
    Command.CommandText = "INSERT INTO SIGN(TYPESIGN_ID) VALUES('" + CStr(Col2) + "')"
End If