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How to connect to a remote database from a C# application

Posted on 2009-05-03
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Last Modified: 2012-05-06
Hello,

I am developing a C# application, the user should be subscripted to use the program. The program should query if the username and password is correct from a remote database. I'm using MS SQL Server 2008 as the database. How can I first establish a connection, -do I need to change some permissions, open ports etc- and then how can I retrieve the query result? Can you give me a clear explanation or a link?

Thanks in advance.
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Question by:guveniscan
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Cebik earned 500 total points
ID: 24290546
On machine where you have mssql installed make shure that you have enabled TCP/IP in SQL Server Configuration Manager -> SQL server xxxx network configurator -> Protocols for..

TCP/IP = enabled
named pipes = enabled (i'm not sure if this one is needed)

add exception in firewall - TCP 1433 for both machines

//connecting
//set source, dbname, username and passwd before
 
Console.WriteLine("Data Source     = " + source); //"(local)" or "computername"
Console.WriteLine("Initial catalog = " + dbname);
Console.WriteLine("User ID         = " + username);
Console.WriteLine("User password   = " + passwd);
 
SqlConnectionStringBuilder dbInfo = new SqlConnectionStringBuilder();
string connectionString = "Data Source=" + source + ";Initial catalog=" + dbname + ";User ID=" + username + ";Persist Security Info=True;";
string pass = passwd;
 
dbInfo.ConnectionString = connectionString;
dbInfo.Password = pass;
                
SqlConnection mssql = new SqlConnection();
mssql.ConnectionString = dbInfo.ConnectionString;
mssql.Open();
 
//readingSqlCommand mpCmd = mssql.CreateCommand();
mpCmd.CommandText =
      "SELECT object_id from s4.objects where class_id = 17";
 
SqlDataReader mpRdr = mpCmd.ExecuteReader();
while (mpRdr.Read())
{
    int id = mpRdr.GetInt32(0);
    Console.Writelind(id.ToString());
}
 
mpRdr.Dispose();
mpCmd.Dispose();
mpRdr.Close();

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Expert Comment

by:Cebik
ID: 24290556
sorry..
line 20

//reading
SqlCommand mpCmd = mssql.CreateCommand();

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by:Cebik
ID: 24290610
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Author Comment

by:guveniscan
ID: 24291572
Thanks for your concern. Now It is giving the SQL Exception in mssql.open line.

A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: TCP Provider, error: 0 - No connection could be made because the target machine actively refused it.)

I enabled TCP/IP and named pipes, WIndows Firewall is turned off, port 1433 is open and sql browser service is started.

I'm using the same computer for client and server machines  and I'm using Windows Authentication, Can they be the problems?
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by:Cebik
ID: 24292824
i think yes.. add some user or make mixed mode auth.. (user: sa)
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by:Cebik
ID: 24292845
adding user
osql -E -Q sp_addogin username, userpasswd

but more efficient (like windows auth) is mixed mode
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Author Comment

by:guveniscan
ID: 24292974
I have enabled the mixed mode through Server Properties->Security->Server Authentication. I've added a new login (with public privileges) from the GUI and am able to login with this user in Management Studio. But I still cannot establish a remote connection from the client application. It still raises exception in mssql.open line.
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Expert Comment

by:Cebik
ID: 24293027
when you enable tcp/ip you must restart mssql services or reset computer..
and show me your connection string
PS (local) or 127.0.0.1
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Expert Comment

by:Cebik
ID: 24293079
you must have also SQL Server and SQL Server Browser runung..
start them if it isn't started (start and stop this if you change settings below)
i've got all enabled in protocols (shared memory, named pipes, tcp/ip, via)
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Author Comment

by:guveniscan
ID: 24293087
I restarted the services when I changed smt. My connection string is below.

"Data Source=81.215.xxx.xx;Initial catalog=MyDatabaseName;User ID=UserID;Persist Security Info=True;"

I'm using the code you provided, password is added in the later line "dbInfo.password"

I have SQL Server 2008 installed and SQL Server Express 2005 has come with Visual Studio. Should I modify the data source to smt like 81.215.xxx.xx\servername\instancename ?

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Expert Comment

by:Cebik
ID: 24293099
yes..
if this instance isn't default instance then you must add it..
i will check where :)
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Author Comment

by:guveniscan
ID: 24293116
I have shared memory, named pipes, tcp/ip enabled. But when VIA is enabled I cannot restart SQLServer service. It gives an error, I should disable it to restart the service.
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Expert Comment

by:Cebik
ID: 24293145
i dont think so... live it disabled then..
and...

DataSource=".\SQLinstanceNAME"
or
DataSource="172.16.10.200\SQLinstanceName"
or
DataSource="computerName\SQLinstanceName"
or
Data Source=.\SQLExpress;Initial catalog=dbName;User ID=sa;Persist Security Info=True;

or
Change SQL Instance name to default(local) instance
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Expert Comment

by:Cebik
ID: 24293153
As far as I know we cannot change/switch a default instance with  a named
 one. Re-install SQL Server only.
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Author Comment

by:guveniscan
ID: 24293816
The program is working in another network location. I guess the problem is about my router, I'm using DSL connection. My friend told me I have to play with NAT settings, so the router can forward the request to the server machine.  
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Expert Comment

by:Cebik
ID: 24293838
shure..

try first this on the same machine

when it will be work than you can forward required port
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Expert Comment

by:Cebik
ID: 24293845
you can try to test connection from command line..
install mssql express or other..

and try to login to second computer database:

osql -ScomputernameOrIP -Usa -Ppassword

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