ASP.NET数据访问层的概念是什么

usingSystem;  usingSystem.Data;  usingSystem.Data.SqlClient;  usingSystem.Configuration;  usingSystem.Web;  usingSystem.Web.Security;  usingSystem.Web.UI;  usingSystem.Web.UI.WebControls;  usingSystem.Web.UI.WebControls.WebParts;  usingSystem.Web.UI.HtmlControls;  usingSystem.Text;  ///<summary> ///数据访问层，数据库操作类  ///summary> publicclassDatabase  {  publicstaticstringConnectionStrings=ConfigurationManager.ConnectionStrings["ConnectionStrings"].ConnectionString;  ///<summary> ///执行带SqlParameter的sql语句，成功返回true，失败返回false  ///summary> ///<paramnameparamname="sql">sql语句param> ///<paramnameparamname="Param">SqlParameter[]参数列表param> ///<returns>returns> publicstaticintExecuteNonQuery(stringsql,paramsSqlParameter[]Param)//执行带SqlParameter的sql语句，返回影响的行数  {  //HttpContext.Current.Response.Write(sql+"<br>");  using(SqlConnectionconn=newSqlConnection(ConnectionStrings))  {  if(conn.State!=ConnectionState.Open)  conn.Open();  SqlTransactionTran=conn.BeginTransaction();//开始事务  SqlCommandcmd=newSqlCommand(sql,conn,Tran);  if(Param!=null)  cmd.Parameters.AddRange(Param);  try  {  intResult=cmd.ExecuteNonQuery();  Tran.Commit();  cmd.Parameters.Clear();  returnResult;  }  catch(Exceptionerr)  {  HttpContext.Current.Response.Write(err.Message+"<br>"+err.StackTrace);  Tran.Rollback();//回滚事务  return0;  }  }  }  ///<summary> ///执行带SqlParameter的sql，返回DataReader  ///summary> ///<paramnameparamname="sql">sql语句param> ///<paramnameparamname="Param">SqlParameter[]参数列表param> ///<returns>返回SqlDataReaderreturns> publicstaticSqlDataReaderExecuteReader(stringsql,paramsSqlParameter[]Param)//执行带SqlParameter的sql，返回DataReader  {  SqlConnectionconn=newSqlConnection(ConnectionStrings);  SqlCommandcmd=newSqlCommand(sql,conn);  if(Param!=null)  cmd.Parameters.AddRange(Param);  if(conn.State!=ConnectionState.Open)  conn.Open();  try  {  SqlDataReaderdr=cmd.ExecuteReader(CommandBehavior.CloseConnection);  cmd.Parameters.Clear();  returndr;  }  catch(Exceptionerr)  {  conn.Close();  HttpContext.Current.Response.Write(err.Message+"<br>"+err.StackTrace);  returnnull;  }  }  ///<summary> ///执行带SqlParameter的sql，返回DataTable  ///summary> ///<paramnameparamname="sql">SQL语句param> ///<paramnameparamname="Param">SqlParameter[]参数列表param> publicstaticDataTableGetDataTable(stringsql,paramsSqlParameter[]Param)//执行带SqlParameter的sql，返回DataTable  {  SqlConnectionconn=newSqlConnection(ConnectionStrings);  DataTabledt=newDataTable();  SqlDataAdapterda=newSqlDataAdapter(sql,conn);  if(Param!=null)  da.SelectCommand.Parameters.AddRange(Param);  SqlCommandBuildercb=newSqlCommandBuilder(da);  da.Fill(dt);  conn.Close();  //HttpContext.Current.Response.Write(sql+"<br>");  returndt;  }  ///<summary> ///执行带SqlParameter的sql，返回查询结果***行***列的数据  ///summary> ///<paramnameparamname="sql">SQL语句param> ///<paramnameparamname="Param">SqlParameter[]参数列表param> ///<returns>returns> publicstaticObjectExecuteScalar(stringsql,paramsSqlParameter[]Param)//执行带SqlParameter的sql，返回查询结果***行***列的数据  {  //HttpContext.Current.Response.Write(sql+"<br>");  using(SqlConnectionconn=newSqlConnection(ConnectionStrings))  {  if(conn.State!=ConnectionState.Open)  conn.Open();  SqlTransactionTran=conn.BeginTransaction();  SqlCommandcmd=newSqlCommand(sql,conn,Tran);  if(Param!=null)  cmd.Parameters.AddRange(Param);  try  {  objectResult=cmd.ExecuteScalar();  cmd.Parameters.Clear();  Tran.Commit();  returnResult;  }  catch(Exceptionerr)  {  HttpContext.Current.Response.Write(err.Message+"<br>"+err.StackTrace);  Tran.Rollback();  returnnull;  }  }  }  ///<summary> ///生成SqlParameter参数  ///summary> ///<paramnameparamname="ParamName">参数名param> ///<paramnameparamname="paramType">参数类型param> ///<paramnameparamname="ParamValue">参数的值param> publicstaticSqlParameterGetParameter(stringParamName,SqlDbTypeparamType,ObjectParamValue)//生成SqlParameter参数  {  SqlParameterparam=newSqlParameter(ParamName,paramType);  param.Value=ParamValue;  returnparam;  }  }