C# MySQL Connection problems

Question

I'm trying to connect a C# application (using Visual C# 2008 Express Edition) to a remote MySQL server. I have the drivers for this, but when I followed the tutorials (including adding the pooling and connection reset properties), I get an error that: Object reference not set to an instance of an object. I've included the two lines of code that should be making a connection. The error is thrown on the second line.

        MySqlConnection connect = new MySqlConnection("database=d*******;Data Source=mysql.netfirms.com;user id=*******;pwd=*****;pooling=false;connection reset=false");
        connect.Open();

unlikely, as I downloaded the libraries yesterday, and based on the dates in that bug, the patch should be included in the current release. — Elie
– Elie, Commented Dec 31, 2008 at 23:21
Can you add the stack Trace to this? I think that would be helpful... — Frank V
– Frank V, Commented Apr 24, 2009 at 17:59
The issue was related to my server in the end. The datasource, while properly defined, could not be located, but it was not giving a sensible error message. — Elie
– Elie, Commented Apr 24, 2009 at 19:25

Ricardo Villamil · Accepted Answer · 2008-12-31 18:04:13Z

2

I'd try setting the connection string outside of the constructor to help narrow down the issue:

MySqlConnection connect = new MySqlConnection();
//Do you get the null exception in this next line?
connect.ConnectionString = "your conn string here";
connect.Open(); //-> If you get the exception here then the problem is with the connection string and not the MySqlConnection constructor.

If you do get the exception in the connect.ConnectionString = ... line, then the problem is with the driver and sounds like you need to reinstall it.

I would also try a simpler connection string, without the pooling and reset keys.

edited Dec 31, 2008 at 18:04

answered Dec 31, 2008 at 17:33

Ricardo Villamil

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3 Comments

Elie Over a year ago

I get the exception on the connect.Open(); line. I added the pooling and reset keys based on a response to someone with a similar problem, but it didn't make any difference.

Daniel Schneller Over a year ago

Can C# really return null from a constructor? In Java that's impossible. Either you get a valid object reference or an Exception is thrown.

Ricardo Villamil Over a year ago

No, but the constructor itself can reference a null object within its body, therefore throwing a null reference exception.

Daniel Moore · Accepted Answer · 2009-04-23 19:02:25Z

1

Can you post more code? The exception line is probably a bit off due to compiler optimization or related. Constructors must return an object or throw an exception. It is impossible to say

MyType item = new MyType();
Debug.Fail(item == null); // will never fail.

The null reference is probably on the line just above your instantiation.

answered Apr 23, 2009 at 19:02

Daniel Moore

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