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I’m trying to make A winform CRUD operations app using SQL server but, when running program and perform query, the program said 

ConnectionString is not initialized
.

Even I’ve added the new connection to the existing database and copy the exact the connection string.

I have a class like

public partial class PersonContactForm : Form {
   //  I declared my connect db here
   SqlConnection sqlCon = new SqlConnection(@"Data Source=DESKTOP-JIV4OD1SQLEXPRESS;Initial Catalog=DapperCrud; Integrated
   
   // some code 

  // my test db connect. It does work
  private void btnTestSqlConn_Click(object sender, EventArgs e)
        {
            using (sqlCon = new SqlConnection(@"Data Source=DESKTOP-JIV4OD1SQLEXPRESS;Initial Catalog=DapperCrud; Integrated Security=True;"))
            {
                try {
                    sqlCon.Open();
                } catch(SqlException sqlEx)
                {
                    MessageBox.Show(sqlEx.Message);
                }

                MessageBox.Show("Connection to SQL OK!");
                return;
            }
        }

   // this is a save database. When I clicked on this button. 
   // the error ConnectionString is not initialized occurred.
   private void btnSave_Click(object sender, EventArgs e)
        {
            try
            {
                // if sql state is closed so open it
                if (sqlCon.State == ConnectionState.Closed)
                    sqlCon.Open();

                DynamicParameters param = new DynamicParameters();
                param.Add("@contactId", contactId);
                param.Add("@firstName", txbFirstName.Text.Trim());
                param.Add("@lastName", txbLastName.Text.Trim());
                param.Add("@mobile", txbMobile.Text.Trim());
                param.Add("@Address", txbAddress.Text.Trim());

                sqlCon.Execute("ContactAddOrEdit", param, commandType: CommandType.StoredProcedure);
                
                // if contactId == 0 then we saved data succesfully 
                if (contactId == 0)
                    MessageBox.Show("Saved OK!");
                else  
                    MessageBox.Show("Updated OK!");

                // fill into DataGridView
                fillDataGridView();
                // clear textBox fields after filled
                clear();
            } catch(Exception ex)
            {
                MessageBox.Show(ex.Message);
            } finally
            {
                // close sql after executed 
                sqlCon.Close();
            }
        }

   // .... some code
Anonymous Asked question May 14, 2021