三层中SQLHelper.cs类的实现

class SqlHelper
{
protected string connectionString;
protected sqlConnection sqlConnection;
protected sqlCommand;       
public SqlHelper(string connection string){}      //构造函数
public ~SqlHelper(){}         //析构函数
 
private SqlParameter MakeParam(string paramName, SqlDbType dbType, int size, ParameterDirection direction, object value) 
          //内部产生参数
public SqlParameter MakeInParam(string paramName, SqlDbType dbType, int size, object value) //产生输入参数
public SqlParameter MakeOutparam(string paramName, SqlDbType dbType, int size, object value) //产生输出参数

　　　//ExecuteNonQuery
        //ExecuteDataset
        //ExecuteReader
        //ExecuteScalar
        //ExecuteXmlReader

//ExecuteNonQuery相关的重载函数。
public int ExecuteNonQuery(string connectionString,CommandType commandType,string commandText);
public int ExecuteNonQuery(string connectionString,CommandType commandType,string commandText,SqlParameter[]  commandparameters);
public int ExecuteNonQuery(string connectionString,string spName,object[] parameterValues);
public int ExecuteNonQuery(Sqlconnection connection,CommandType commandType,string commandtext);
public int ExecuteNonQuery(SqlConnection connection,CommandType commandType,string commandText,
 params SqlParameter[] commandParameters);
public int ExecuteNonQuery(SqlConnection connection,string spName,object[] parameterValues);
public int ExecuteNonQuery(SqlTransaction transaction,CommandType commandType,string commandText);
public int ExecuteNonQuery(SqlTransaction transaction,CommandType commandType,string commandText,
 SqlParameter[] commandParameters);
public int ExecuteNonQuery(SqlTransaction transaction,string spName,object[] parameterValues);

}

sqlhelper中如何得到连接字符串呢？

DAL中添加System.web 和System.configuration引用。

直接读取web.config

web项目中引用DAL