I am currently working on a C# project that will export MySQL Data. The export is for any database within the server so I am not going to know what fields and the data types that are in the table and I am not going to know if a field in the table allows null values or not.
During testing, I have found that the export is working fine but if the field allows null when the mysql data reader goes gets to the row which is null it displays an error SqlNullValueException, data is null.
I have tried doing if (reader.getString(field) == null) {}
but it is still displaying the error.
How do I cope with Null values in the database.
Thanks for any help you can provide.
In this blog Post there is an good extension method for the reader
SQL Data Reader - handling Null column values
I Changed it to the IDataReader Interface
You need to test for null explicitly in a reader so:
You could always use the c# conditional operator '?' like so...
You can compare the object that retrive from NULL field with DBNull.Value.
I have had problems with using the GetString() method on fields that allow null values. I worked around this by doing something like:
reader[0].ToString()
.Net does not use a
null
literal to distinguish database nulls. I can only speculate, but I suspect the reason for this is that many common database column types (int, float, etc) are value types, and comparing a value type to null won't work at all how you expect.Instead, check for
DBNull.Value
or use the.IsDbNull()
function.