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();
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.
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.
Related
Authentication to host '127.0.0.1' for user 'root' using method 'mysql_native_password' failed with message: Reading from the stream has failed.
I've searched a lot about this issue and only Internet disconnect solved the problem. Why is that?
I use MYSQL 8 and C# winforms.
Connection code looks like this:
MySqlConnection conn = new MySqlConnection("datasource=127.0.0.1;username=root;password=password;database=my_tests");
The every next try I execute the command is successful! It happens only first time.
I very appreciate your time people. And would be very thankful for constructive help for a newbie like me.
When I put SslMode=None to a string so it looks like
MySqlConnection conn = new MySqlConnection("datasource=127.0.0.1;username=root;password=password;database=my_tests;SslMode=None");
the problem is gone. But I'm not sure if I want not to use it. Any other solutions would be great.
try this code you can use the server ip address instead of local
string connectionString = "server=(local)\SQLExpress;database=my_tests;password:qwerty;integrated Security=SSPI;";
SqlConnection _con = new SqlConnection(connectionString)
When calling the Open() method on a SqlConnection instance that got passed an incomplete connection string, the method does not throw an exception.
I have created the following example to showcase my problem.
var success = true;
var connectionStrings = new[]
{
"Integrated Security=SSPI;",
"Initial Catalog=awdemo;Integrated Security=SSPI;",
"Data Source=.\\sql2016;Initial Catalog=awdemo;Integrated Security=SSPI;"
};
foreach (var connectionString in connectionStrings)
{
var conn = new SqlConnection(connectionString);
try
{
conn.Open();
}
catch (Exception)
{
success = false;
}
finally
{
conn.Close();
Console.WriteLine($"{connectionString} - Success = {success}");
}
}
Result:
Integrated Security=SSPI; - Success = True
Initial Catalog=awdemo;Integrated Security=SSPI; - Success = True
Data Source=.\sql2016;Initial Catalog=awdemo;Integrated Security=SSPI; - Success = True
I would expect conn.Open() to throw an exception for the first two connection strings, since both of them are incomplete and not valid.
Why is there no exception thrown?
EDIT: as pointed out by Steve in the comments an exception is not thrown because the component connects to my default instance of SQL Server when not providing the server information.
Is there a way to force the SqlConnection component to throw an error on incomplete connection strings? In the application it is possible and allowed to create incomplete connection strings.
There's no practical way to fully validate this. You could have a connection string that has all of the components you expect, including a valid server and database name, but it's the wrong server or wrong database.
So if the expectation is that the class should fail on conn.Open() if the connection string is incorrect (not invalid, but incorrect), you can't completely achieve that.
Does it matter? Imagine a few scenarios, all of which include incorrect connection strings:
The connection string is "blarg!" and so attempting to open the connection throws an exception.
The connection string doesn't contain a server or database name. You can open the connection but when you try to execute some command it fails.
The connection string contains a server and database name, but it's the wrong server or database. It fails for the same reason as 2.
In each of the scenarios, what's the first thing you're going to do? You're going to look at the exception. Regardless of which line throws it, you're going to quickly deduce that you have the wrong connection string.
So a "validation" which can't actually validate the connection string before you open it is just going to add work. If the connection string is wrong, that truly is an "exceptional" condition so it's probably better to just let the code throw an exception where it does. You'll find the problem quickly.
All of that aside, suppose you just really want to be sure that your connection contains a server name and a database name before you try to open it. You could write an extension method like this:
// Maybe give it a better name.
public static void ValidateThatConnectionHasDataSourceAndDatabase(this SqlConnection connection)
{
if (string.IsNullOrEmpty(connection.DataSource))
throw new Exception("The connection has no datasource");
if (string.IsNullOrEmpty(connection.Database))
throw new Exception("The connection has no database");
}
After you create the connection and before you open it, call conn.ValidateThatConnectionHasDataSourceAndDatabase();
I'm new to C# and connecting to databases.
The problem is: whenever I try to connect to DB by running this code:
string connparams = "server=127.0.0.1;uid=root;pwd=12345;database=test;";
try
{
MySqlConnection connection = new MySqlConnection(connparams);
}
catch (System.ArgumentException me)
{
Console.WriteLine(me.ToString());
}
connection.Open();
connection.Close();
I get the window "The application is in break mode"
When I take a look at the events window I can see an exception with description "No source code". When I try to see the implementations of functions in MySQLConnection I can see none of them, only declarations. So what should I do/redo/reinstall in order to solve this? Using VS2017, .NET Framework 4.6.1, Connector/NET (MySQL)
I am using this code but getting an error of 'Object reference not set to an instance of an object.' at con.open() ? what am I doing wrong ?
I have already download and installed ODAC component version 10 , 11 ,12 trying each one at the failure of the latest one but still same error
using Oracle.DataAccess.Client;
namespace WindowsFormsApplication1
{
class OraTest
{
public OracleConnection con = new OracleConnection();
public void Connect()
{
con.ConnectionString = "Data Source=(DESCRIPTION= (ADDRESS = (PROTOCOL = TCP)(HOST =myip) (PORT = myport))(CONNECT_DATA = (SERVER = dedicated)(SERVICE_NAME = mydb)));User ID=myid;Password=mypass;";
con.Open(); //error here
}
public void Close()
{
con.Close();
con.Dispose();
}
}
Please go through this link
Getting Started with Oracle Data Provider for .NET (C# Version)
http://www.oracle.com/webfolder/technetwork/tutorials/obe/db/dotnet/GettingStartedNETVersion/GettingStartedNETVersion.htm
If you add a try/catch block in Connect(), you'll be able to catch the error.
For example:
When opening an oracle connection, connection object is null
I added the try catch block, and it returned ORA12154 - TNS could not
be resolved. After some research, I added an SID to my tnsnames.ora
file in my ODP for .NET Oracle home path, and it worked
See also Troubleshooting Oracle Net Services for troubleshooting possible connection issues from Oracle clients (such as your C# program).
But your first step is absolutely to determine the Oracle-level error (for example, ORA-12543 (could not connect to server host) or TNS-12514 (could not find service name)
MSDN: OracleException Class
public void ShowOracleException()
{
OracleConnection myConnection =
new OracleConnection("Data Source=Oracle8i;Integrated Security=yes");
try
{
myConnection.Open();
}
catch (OracleException e)
{
string errorMessage = "Code: " + e.Code + "\n" +
"Message: " + e.Message;
System.Diagnostics.EventLog log = new System.Diagnostics.EventLog();
log.Source = "My Application";
log.WriteEntry(errorMessage);
Console.WriteLine("An exception occurred. Please contact your system administrator.");
}
}
It's significant that con.ConnectionString = xyz works, but the following `con.Open()" fails. This means .Net is creating the C# object, but Oracle/TNS is failing when you try to use it.
ADDITIONAL SUGGESTIONS:
Re-read
When opening an oracle connection, connection object is null.
Read all of the suggestions, including the one about "Data Source in your connection string".
Focus on your connection string. It couldn't hurt to specify the connection string in your OracleConnection() constructor, if possible. Here's another link:
ODP.NET Connection exception
It would be great if you can verify connectivity from your PC with some other Oracle client, besides your C#/.Net program. To verify you're talking to the right TNS host and service, with the correct username/password. For example, maybe you have SQLDeveloper or sqlplus.
Finally, re-read the TNS troubleshooting link:
https://docs.oracle.com/cd/E11882_01/network.112/e41945/trouble.htm#NETAG016
What worked for me with the same error was to simply switch from the 'plain' Oracle DataAccess library, to the 'Managed' version.
This is an extemely easy change to make -
Add a Reference in your c# project to the Oracle.ManagedDataAccess library
Replace the existing use statements at the top of your Oracle client code with the following:
using Oracle.ManagedDataAccess.Client;
using Oracle.ManagedDataAccess.Types;
Include the Oracle.ManagedDataAccess.dll file with your exe
My problem involves checking if I have a valid database connection before reading from the database. If the database is down I'd like to write to a xml file instead. I have the location of the database (if it's up) at runtime so if the database was working I can create a new sqlConnection to it.
Use a typical try...catch...finally structure, and based on the specific exception type and message, decide whether you want to write to xml or not.
try
{
SqlConnection connection = new SqlConnection(DB("Your DB Name"));
connection.Open();
}
catch (Exception ex)
{
// check the exception message here, if it's telling you that the db is not available. then
//write to xml file.
WriteToXml();
}
finally
{
connection.Close();
}
I would just use something like:
using(SqlConnection conn = new SqlConnection(c)) {
conn.Open();
}
It will throw an exception if invalid. You could write to the xml in the exception.
An easy way would be to execute a simple query and see if an error occurs:
For Oracle:
SELECT * FROM DUAL
For SQL Server
SELECT 1
Basicly just some kind of relatively "free" query that will let you know that the database is up and running and responding to requests and your connection hasn't timed out.
You cannot really tell whether the DB is up and running without actually opening a connecting to it. But still, connection might be dropped while you're working with it, so this should be accounted for.