How to handle Db nulls

Question

User56849873 posted

I am retrieving a database object and trying to set the values of the object's fields to various textboxes in my vb.net page.

 

However, since some of the database fields have null values, I am getting the following error.

System.InvalidOperationException: Nullable object must have a value.

 How do I solve this problem? 

Answer 1

User-442214108 posted

You should handle nulls in much like you should handle exceptions

When populating your textboxes, check System.DBNull.Value first. Textboxes must be populated with a string. If it's null (System.DBNull.Value) either don't populate the Textbox, or populate with empty string (your choice) 

you might check out this link:
http://www.aspnet101.com/2008/02/handling-database-nulls-with-a-datareader/

 

Answer 2

User3690988 posted

You can also check for NULL in your SQL SELECT statement and set a value there:

SELECT IsNull(OfficeName,'') AS OfficeName, ...

If you have access to the SQL.

Answer 3

User-952121411 posted

Good question, and yes you must check if a value is null 1st or that exception will occur.  I will give you the syntax to check for database null values using IsDbNull for pulling feilds directly out of a DataSet and onto a TextBox control.  However, the source data object (DataSet) is not the focal point here, you can apply this code to other situations too.

For Each dr As DataRow In ds.Tables(0).Rows
   If Not IsDBNull(dr("FirstName")) Then Me.txtFirstName.Text = dr("FirstName").ToString()
   If Not IsDBNull(dr("LastName")) Then Me.txtLastName.Text = dr("LastName").ToString()
   If Not IsDBNull(dr("Phone")) Then Me.txtPhoneNum.Text = Integer.Parse(dr("FirstName"))

Next

 Hope this helps!