Why connection string in Web.config file only?

In this article we will learn about
1. Storing connection strings  in a configuration file. For example, web.config for an asp.net web application and app.config for windows application
2. Reading the connection strings from web.config and app.config files.
3. Disadvantages of storing connection strings in application code.
4. Advantages of storing connection string in configuration files - web.config and app.config.



There are 2 issues with hard coding the connection strings in application code
1. For some reason, if we want to point our application to a different database server, we will have to change the application code. If you change application code, the application requires a re-build and a re-deployment which is a time waster.
2. All the pages that has the connection string hard coded needs to change. This adds to the maintenance overhead and is also error prone.

In real time, we may point our applications from time to time, from Development database to testing database to UAT database.

Because of these issues, the best practice is to store the connection in the configuration file, from which all the pages can read and use it. This way we have only one place to change, and we don't have to re-build and re-deploy our application. This saves a lot of time.

In an asp.net web application, the configuration strings can be stored in web.config file, as shown below. Give a meaningful name to your connection string. Since we are working with sql server, the provider name is System.Data.SqlClient.
<connectionStrings>
  <add name="DatabaseConnectionString"
        connectionString="data source=.; database=Sample_Test_DB; Integrated Security=SSPI"
        providerName="System.Data.SqlClient" />
</connectionStrings> 



How to read the connection string from web.config file?
Use the ConnectionStrings property of the ConfigurationManager class to retrieve the connection string value from web.config. ConfigurationManager class is present in System.Configuration namespace.
protected void Page_Load(object sender, EventArgs e)
{
    string ConnectionString = ConfigurationManager.co .ConnectionStrings["DatabaseConnectionString"].ConnectionString;
    using (SqlConnection connection = new SqlConnection(ConnectionString ))
    {
        SqlCommand cmd = new SqlCommand("Select * from tblProductInventory", connection);
        connection.Open();
        GridView1.DataSource = cmd.ExecuteReader();
        GridView1.DataBind();
    }
}

The configuration file in a windows application is App.config. Storing connection strings in App.config is similar to web.config. The same ConfigurationManager class can be used to read connection string from App.config file. The example below, shows how to read connection strings from App.config file, and bind the data to a DataGridview control in a windows application.
private void Form1_Load(object sender, EventArgs e)
{
    string ConnectionString = ConfigurationManager.ConnectionStrings["DatabaseConnectionString"].ConnectionString;
    using (SqlConnection connection = new SqlConnection(ConnectionString ))
    {
        SqlCommand cmd = new SqlCommand("Select * from tblProductInventory", connection);
        connection.Open();
        BindingSource source = new BindingSource();
        source.DataSource = cmd.ExecuteReader();
        dataGridView1.DataSource = source;
    }
}