本文模仿實現數據庫訪問的通用類，代碼清晰，而且很實用，包括了對數據庫的所有的常用的操作。

  /// <summary>  /// 數據庫訪問通用類  /// </summary>  public class SqlHelper  {  private string connectionString;  /// <summary>  /// 設定數據庫訪問字符串  /// </summary>  public string ConnectionString  {  set { connectionString = value; }  }  /// <summary>  /// 構造函數  /// </summary>  /// <param name="connectionString">數據庫訪問字符串</param>  public SqlHelper(string connectionString)  {  this.connectionString = connectionString;  }  /// <summary>  /// 執行一個查詢，并返回查詢結果  /// </summary>  /// <param name="sql">要執行的sql語句</param>  /// <param name="commandType">要執行的查詢語句的類型，如存儲過程或者sql文本命令</param>  /// <returns>返回查詢結果集</returns>  public DataTable ExecuteDataTable(string sql,CommandType commandType)  {  return ExecuteDataTable(sql, commandType, null);  }  /// <summary>  /// 執行一個查詢，并返回結果集  /// </summary>  /// <param name="sql">要執行的sql文本命令</param>  /// <returns>返回查詢的結果集</returns>  public DataTable ExecuteDataTable(string sql)  {  return ExecuteDataTable(sql, CommandType.Text, null);  }  /// <summary>  /// 執行一個查詢，并返回查詢結果  /// </summary>  /// <param name="sql">要執行的sql語句</param>  /// <param name="commandtype">要執行查詢語句的類型，如存儲過程或者sql文本命令</param>  /// <param name="parameters">Transact-SQL語句或者存儲過程參數數組</param>  /// <returns></returns>  public DataTable ExecuteDataTable(string sql, CommandType commandtype, SqlParameter[] parameters)  {  DataTable data = new DataTable(); //實例化datatable，用于裝載查詢結果集  using (SqlConnection con = new SqlConnection(connectionString))  {  using (SqlCommand cmd = new SqlCommand(sql, con))  {  cmd.CommandType = commandtype;//設置command的commandType為指定的Commandtype  //如果同時傳入了參數，則添加這些參數  if (parameters != null)  {  foreach (SqlParameter parameter in parameters)  {  cmd.Parameters.Add(parameter);  }  }  //通過包含查詢sql的sqlcommand實例來實例化sqldataadapter  SqlDataAdapter adapter = new SqlDataAdapter(cmd);  adapter.Fill(data);//填充datatable  }  }  return data;  }  /// <summary>  /// 返回一個SqlDataReader對象的實例  /// </summary>  /// <param name="sql">要執行的SQl查詢命令</param>  /// <returns></returns>  public SqlDataReader ExecuteReader(string sql)  {  return ExecuteReader(sql, CommandType.Text, null);  }  /// <summary>  ///  /// </summary>  /// <param name="sql">要執行的sql語句</param>  /// <param name="commandType">要執行查詢語句的類型，如存儲過程或者SQl文本命令</param>  /// <returns></returns>  public SqlDataReader ExecuteReader(string sql,CommandType commandType)  {  return ExecuteReader(sql, commandType, null);  }  /// <summary>  /// 返回一個sqldatareader對象的實例  /// </summary>  /// <param name="sql"></param>  /// <param name="commandType"></param>  /// <param name="parameters"></param>  /// <returns></returns>  public SqlDataReader ExecuteReader(string sql, CommandType commandType, SqlParameter[] parameters)  {  SqlConnection con = new SqlConnection(connectionString);  SqlCommand cmd = new SqlCommand(sql, con);  if (parameters != null)  {  foreach (SqlParameter parameter in parameters)  {  cmd.Parameters.Add(parameters);  }  }  con.Open();  //CommandBehavior.CloseConnection參數指示關閉reader對象時關閉與其關聯的Connection對象  return cmd.ExecuteReader(CommandBehavior.CloseConnection);  }  /// <summary>  /// 執行一個查詢，返回結果集的首行首列。忽略其他行，其他列  /// </summary>  /// <param name="sql">要執行的SQl命令</param>  /// <returns></returns>  public Object ExecuteScalar(string sql)  {  return ExecuteScalar(sql, CommandType.Text, null);  }  /// <summary>  ///  /// </summary>  /// <param name="sql"></param>  /// <param name="commandType"></param>  /// <returns></returns>  public Object ExecuteScalar(string sql, CommandType commandType)  {  return ExecuteScalar(sql, commandType, null);  }  /// <summary>  ///  /// </summary>  /// <param name="sql"></param>  /// <param name="commandType">參數類型</param>  /// <param name="parameters"></param>  /// <returns></returns>  public Object ExecuteScalar(string sql,CommandType commandType, SqlParameter[] parameters)  {  Object result=null;  SqlConnection con=new SqlConnection(connectionString);  SqlCommand cmd=new SqlCommand(sql,con);  cmd.CommandType= commandType;  if(parameters!=null)  {  foreach (SqlParameter parapmeter in parameters)  {  cmd.Parameters.Add(parapmeter);  }  }  con.Open();  result=cmd.ExecuteScalar();  con.Close();  return result;  }  /// <summary>  /// 對數據庫進行增刪改的操作  /// </summary>  /// <param name="sql">要執行的sql命令</param>  /// <returns></returns>  public int ExecuteNonQuery(string sql)  {  return ExecuteNonQuery(sql, CommandType.Text, null);  }  /// <summary>  /// 數據庫進行增刪改的操作  /// </summary>  /// <param name="sql">對數據庫進行操作的sql命令</param>  /// <param name="commandType">要執行查詢語句的類型，如存儲過程或者sql文本命令</param>  /// <returns></returns>  public int ExecuteNonQuery(string sql, CommandType commandType)  {  return ExecuteNonQuery(sql, commandType, null);  }  /// <summary>  /// 對數據庫進行增刪改的操作  /// </summary>  /// <param name="sql">要執行的sql語句</param>  /// <param name="commandType">要執行的查詢語句類型，如存儲過程或者sql文本命令</param>  /// <param name="parameters">Transact-SQL語句或者存儲過程的參數數組</param>  /// <returns></returns>  public int ExecuteNonQuery(string sql, CommandType commandType, SqlParameter[] parameters)  {  int count = 0;  SqlConnection con = new SqlConnection(connectionString);  SqlCommand cmd = new SqlCommand(sql, con);  cmd.CommandType = commandType;  if (parameters != null)  {  foreach(SqlParameter parameter in parameters)  {  cmd.Parameters.Add(parameter);  }  }  con.Open();  count = cmd.ExecuteNonQuery();  con.Close();  return count;  }  /// <summary>  /// 返回當前連接的數據庫中所有用戶創建的數據庫  /// </summary>  /// <returns></returns>  public DataTable GetTables()  {  DataTable table = null;  using (SqlConnection con = new SqlConnection(connectionString))  {  con.Open();  table = con.GetSchema("Tables");  }  return table;  }  }