02장 ADO.NET DB Connection

--  sqlError 처리

protected void btnConnect_Click(object sender, EventArgs e)     {         //Connection         SqlConnection con = new SqlConnection();         con.ConnectionString =                 "server=.;database=Market;uid=Market;pwd=1234;";                       //Command         SqlCommand cmd = new SqlCommand                                     ("Select *From categories", con);         cmd.CommandType = CommandType.Text;         //Data Reader         try         {             con.Open();             SqlDataReader dr = cmd.ExecuteReader();             this.lblError.Text = "연결완료";                         con.Close();         }         catch (SqlException se)         {             SqlErrorCollection sec = se.Errors;             //에러를 묶어서 출력 (예외 처리 의해 에러 발생)             string msg = "";             foreach (var item in sec) //[3] 에러 하나를 담는 클래스             {                 msg += item.ToString() + "<br />"; //.Message : 에러 메시지             }             this.lblError.Text = msg;         }     }

--sqlConnectionWithUsing

public partial class FrmSqlConnectionWithUsing : System.Web.UI.Page {     private string ConnectionString; //필드 : 데이터베이스 연결문자열 저장     //생성자(Ctor + 탭 + 탭)     public FrmSqlConnectionWithUsing()     {         ConnectionString =                        "server=.;database=Market;uid=Market;pwd=1234;";     }     protected void Page_Load(object sender, EventArgs e)     {             //Empty     }     protected void btnConnection1_Click(object sender, EventArgs e)     {         SqlConnection con = new SqlConnection(ConnectionString);         con.Open();         this.lblDisplay.Text = "연결완료";                 con.Close(); //using구문 사용하면 생략 가능     }     protected void btnConnection2_Click(object sender, EventArgs e)     {         //using()안에서 생성된 DB는 using 구문이 끝나면 자동으로 닫힌다.         using (SqlConnection con = new SqlConnection(ConnectionString))         {             con.Open();             this.lblDisplay.Text = "연결완료";                    } //using 구문의 마지막 } 가 실행되면 ,자동으로 Close되므로 생략 가능     } }

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