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C#: SQL Server Connection String

I am trying to use a button that will add to my two columns in my database. I have placeholder values in there currently but will eventually be using 2 pop ups to read in those values.
My question is: how do I get the connection string? I don't know what to put there or where to get that data.
private void button_AddPartNumber_Click(object sender, EventArgs e)
{
string cmdString = "INSERT INTO Part_Numbers (Part_Number, Barcode_Number) VALUES (#val1, #val2)";
string connectionString = "I DONT KNOW WHAT TO PUT HERE";
using (SqlCommand connection = new SqlCommand(connectionString))
{
using (SqlCommand comm = new SqlCommand())
{
comm.Connection = connectionString;
comm.CommandText = cmdString;
comm.Parameters.AddWithValue("#val1", "L-0G004-0830-xx"); //placeholder value
comm.Parameters.AddWithValue("#val2", "asdf1234"); // placehold value
}
}
} // end button_AddPartNumber_Click()

Well, what database are you using? For example, SQLServer? Oracle? MySQL?
In SQLServer, at least, the connection string is defined in the web.config, or app.config, and has syntax similar to the following:
<appSettings>
<add key="ConnectionStringName" value="AppName"/>
</appSettings>
<connectionStrings>
<add name="AppName" connectionString="Data Source=DataSourceName; Initial Catalog=DataBaseName; user id=UserID; password=Password" providerName="System.Data.SqlClient"/>
</connectionStrings>
Something like that. There's probably something I'm missing, but without testing it out in your code, I'm blanking on what that might be.
This how you extract the connection string from your code if the connection string is properly set in the web.config:
var connectionString = ConfigurationManager.ConnectionStrings["AppName"].ConnectionString;

Null reference exception in asp .net

we are working on a project in which we need to show places on google map. For places, we are providing latitude and longitude from database. we are facing null reference exception error in the following place:
using (SqlConnection con = new SqlConnection(System.Configuration.ConfigurationManager.
ConnectionStrings["Data Source=KHUSHALI\\SERVER;Initial Catalog=gis;
Integrated Security=True"].ConnectionString))
How to resolve this error please guide me.

Cause of Exception:-
When you say:
System.Configuration.ConfigurationManager.
ConnectionStrings["Data Source=KHUSHALI\\SERVER;Initial Catalog=gis;
Integrated Security=True"]
Since there is no connection string with name Data Source=KhUSHAL.., thus ConnectionStrings will return null and on that you are trying to access ConnectionString property which will result in Null reference exception. Read about this error here.
Basically you are mixing both, either do this:-
string CS ="Data Source=KHUSHALI\\SERVER;Initial Catalog=gis;Integrated Security=True";
using (SqlConnection con = new SqlConnection(CS))
{
//Your code
}
Or fetch it from Web.Config(Preferred way):-
First define the connection in Web.Config:
<connectionStrings>
<add name="Test" connectionString="Data Source=KHUSHALI\\SERVER;Initial Catalog=gis;
Integrated Security=True" providerName="System.Data.SqlClient" />
</connectionStrings>
Then read it like this:-
using (SqlConnection con = new SqlConnection(System.Configuration
.ConfigurationManager.ConnectionStrings["Test"].ConnectionString))
{
//Your code
}

Do you have the ConnectionString in the Web.Config of the UI project?
Fix:
Copy that ConnectionString and Paste in your Web.Config

Your code,
using (SqlConnection con = new SqlConnection(System.Configuration.ConfigurationManager.
ConnectionStrings["Data Source=KHUSHALI\\SERVER;Initial Catalog=gis;
Integrated Security=True"].ConnectionString))
is Invalid, this is not the way to declare connection string and access them.
How can we declare Connection Strings and can Access them??
No1:>In a Page
string strConnectionString="server=localhost;database=myDb;uid=myUser;password=myPass;;
Integrated Security=True";
using (SqlConnection con = new SqlConnection(strConnectionString))
{
}
No2.>Web.Config you can declare then under configuration and appSeting
And Can Access Like:
using (SqlConnection con = new SqlConnection(ConfigurationManager.AppSettings("myConnectionString")))
{
}
No3>Web.Config you can declare then under configuration and connectionStrings
<connectionStrings>
<add name="myConnectionString" connectionString="server=localhost;database=myDb;uid=myUser;password=myPass;" />
</connectionStrings>
And Can Access Like:
using (SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["myConnectionString"].ConnectionString))
{
}

Autocomplete textbox in C# for windows application

when i run this code this error comes..
object reference not set to an instance of an object.
AutoCompleteStringCollection namesCollection = new AutoCompleteStringCollection();
string ConString = ConfigurationManager.ConnectionStrings["ConString"].ConnectionString;
using (SqlConnection con = new SqlConnection(ConString))
{
SqlCommand cmd = new SqlCommand("SELECT NAME FROM CUSTOMER", con);
con.Open();
SqlDataReader reader = cmd.ExecuteReader();
AutoCompleteStringCollection MyCollection = new AutoCompleteStringCollection();
while (reader.Read())
{
MyCollection.Add(reader.GetString(0));
}
txtcname.AutoCompleteCustomSource = MyCollection;
con.Close();
}

Make sure your connection string in web.config something like
<connectionStrings>
<add name="ConString" connectionString="server=localhost;database=myDb;uid=myUser;password=myPass;" />
</connectionStrings>

Problem : i'm sure that you didn't declare the connection string in your config file under <ConnectionStrings> section.
OR
you might have declared it with some defferent Key name but not ConString.
Solution: you should declare the proper Connection String with Name ConString in your config file under <ConnectionStrings> section.
Make sure that your config file either App.Config or web.config has ConnectionString similar to following:
<connectionStrings>
<add name="ConString" connectionString="Data Source=ServerName;Intial Catalog=DatabaseName;UID=userID;Password=password;Integrated Security=True;" />
</connectionStrings>

Compiler Error Message: CS0118: 'System.Configuration.ConfigurationManager.AppSettings' is a 'property' but is used like a 'method'

Compiler Error Message: CS0118: 'System.Configuration.ConfigurationManager.AppSettings' is a 'property' but is used like a 'method'
<add key="ObjConn" value="Provider=SQLOLEDB;Persist Security Info=True;User ID=OMembers;PWD=OMembers;Initial Catalog=Db;Data Source=""/>
strconnection = System.Configuration.ConfigurationManager.AppSettings("ObjConn");
sqlcon = new SqlConnection(strconnection);

in C#, do this:
strconnection = System.Configuration.ConfigurationManager.AppSettings["ObjConn"];
sqlcon = new SqlConnection(strconnection);

I believe you're working in C#? You need to access it using index operator:
strconnection = System.Configuration.ConfigurationManager.AppSettings["ObjConn"];

Better to define connection strings in the connection strings section as so:
<connectionStrings>
<add
name="ObjConn"
connectionString="data source=.\SQLEXPRESS;Integrated Security=SSPI;AttachDBFilename=|DataDirectory|aspnetdb.mdf;User Instance=true"
providerName="System.Data.SqlClient"
/>
</connectionStrings>
And instantiate you SqlConnection like this:
strconnection = System.Configuration.ConfigurationManager.ConnectionStrings["ObjConn"].ConnectionString;
sqlcon = new SqlConnection(strconnection);

How to use configuration application block of enterprise library?

I have a list of activity code and full name which is placed in web.config file.
But now they are increased to a large number. So I want to remove that from config file and to create a db and access it with help of configuration application block.
Any ideas would be helpful.

You have to add a App.Config file.
Add the connectionstring to the configuration
<configuration>
<connectionStrings>
<add name="connectionstringname"
connectionString="server=localhost;user id=your_bd_userid;Password=your_db_password;database=your_db_name"
providerName="MySql.Data.MySqlClient" />
</connectionStrings>
</configuration>
Your form code goes here
public void LoadActivityData
{
string cnString = ConfigurationManager.ConnectionStrings["connectionstringname"].ConnectionString;
MySqlConnection myConn = new MySqlConnection(cnString);
DataSet dsActivity = new DataSet();
string selectStr = "SELECT * FROM YourActivityTable";
MySqlDataAdapter adapter = new MySqlDataAdapter(selectStr, myConn);
adapter.Fill(dsActivity, "Activities");
grdView1.DataSource = dsActivity;
}
Use System.Configuration namespace to get the configurationmanager class.