Change EF 6 Connection String at Runtime in Windows Form

Question

The requirement is a Windows Form Application which takes the Server, Database, User ID and Password in a Windows Form and changes the EF connection string accordingly so the project can be used in other computers without changing the code.

After research i've learned there is a way to pass a connection string to EF constructor and i've written this function.

public NorthwindEntities(string connectionString)
            : base(connectionString)
        {
        }

After that i'm assuming i should be able to simply take the values from form and use them. I am trying to take the values as in the example below.

private void button1_Click(object sender, EventArgs e)
        {
            string connectionString = String.Format("metadata=res://*/Model1.csdl|" +
                                                             "res://*/Model1.ssdl|" +
                                                              "res://*/Model1.msl;" +
                                                  "provider=System.Data.SqlClient;" +
                                                "provider connection string="" +
                                                                 "data source={0};" +
                                                             "initial catalog={1};" +
                                                                     "user id={2};" +
                                                                      "password={3}",
                       cbo_server.Text, textBox1.Text, textBox2.Text, textBox3.Text);
            try
            {
                NorthwindEntities obj = new NorthwindEntities(connectionString);
                if (obj.Database.Exists())
                {
                    //Do something
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message, "Warning", MessageBoxButtons.OK, MessageBoxIcon.Error);  
            }

Because EF connection string has metadata pre-fix, i tried to add it manually. However, i'm getting the error:

Keyword not supported: 'data source'.

As you may have noticed i'm new to EF so i don't have wide understanding. I just think there's more to that.