1.通过using调用命名空间

using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using DBUtility;
using System.Data.SqlClient;

2.为同名的Class取别名

using BLLCLass=BLL.Class1;
using ModelsClass=Models.Class1;

  using (OleDbConnection connection = new OleDbConnection(connectionString))
            {
                using (OleDbCommand cmd = new OleDbCommand(SQLString, connection))
                {
                    try
                    {
                        connection.Open();
                        int rows = cmd.ExecuteNonQuery();
                        return rows;
                    }
                    catch (System.Data.OleDb.OleDbException E)
                    {
                        connection.Close();
                        throw new Exception(E.Message);
                    }
                }
            }