Handling NULL in ASP.NET

**Techie** · 23-11-2004

HI

I am using PgSQL as Database. Front End is asp.net.

I am reading values from database using Reader classes. For example

Dim x as string
x= memberReader.getString(0)

Now if the value of memberReader.getString(0) is null then its throwing an error.

Error is like "Object cannot be cast from DBNull to other types". Obviously it will give an error.

So how do I check whether the incoming value is null or not.

Not getting much help from Gooooogle.

Help me as soon as possible

thnx in advance

**bosky101** · 24-11-2004

Handling null values returned from database resultsets is different in .NET from VB6.

this function returns that the value os null

Code:

Public Function IsDBNull(ByVal dbvalue) As Boolean
     Return dbvalue Is DBNull.Value 
End Function

this function changes thevalue from null to ""

Code:

Public Function FixNull(ByVal dbvalue) As String
        If dbvalue Is DBNull.Value Then
            Return ""
        Else
            'NOTE: This will cast value to string if
             'it isn't a string.

            Return dbvalue.ToString
        End If
End Function

**Techie** · 25-11-2004

Hi

Still I have not got the solution.

I created the function as you suggested

Code:

Public Function IsDBNull(ByVal dbvalue) As Boolean
   Return dbvalue Is DBNull.Value 
End Function

And I am using that function to check whether the data that I have read is NULL or not

Code:

        Dim BirthDate as new Date
        Dim memberConnection As New NpgsqlConnection(StudentSpace.Global.ConString)
        Dim memberCommand As NpgsqlCommand
        Dim memberReader As NpgsqlDataReader

        id = uId

        memberCommand = New NpgsqlCommand("select BirthDate from Student where UserID=:ID", memberConnection)
        memberCommand.Parameters.Add(":ID", NpgsqlTypes.NpgsqlDbType.Integer).Value = id
        memberConnection.Open()
        memberReader = memberCommand.ExecuteReader()
        memberReader.Read()

        If Not IsDBNull(memberReader.GetDateTime(0)) Then ' Ur Function Call
            BirthDate = memberReader.GetDateTime(0)
        End If

Then also I am getting the error

Error is Object cannot be cast from DBNull to other types.

What should I do

**dotnetguy** · 21-09-2005

Hello,

i am also a lover for asp.net and happy to meet friends like you.

I suggest you to ask few questions on www.asp.net

if you are seriously planning to study, you should atleast visit here twice
a week.

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just watch out for asp.net 2 on 7th november. It will change your life
and the way you have been programming so far.

dotnetguy