类型“System.Data.SqlClient.SqlDataReader"没有定义构造函数 [英] The type 'System.Data.SqlClient.SqlDataReader' has no constructors defined

问题描述

我在使用 SqlDataReader 时遇到问题.当我尝试运行页面时，我收到错误'System.Data.SqlClient.SqlDataReader' 类型没有定义构造函数".我的目的是在用户没有访问权限时返回字符串值 0，当用户进行评估时返回字符串值 1.下面是我的代码片段.

I have issues with SqlDataReader. I get the error "The type 'System.Data.SqlClient.SqlDataReader' has no constructors defined" when I try running the page. My intention here is to return a string value 0 if the user has not had access or 1 when the user has assess. Below is my code snippet.

public string CheckAssess(string emailAddress, string columnName)
{
    string chkAssess;
    SqlDataReader readAssess;
    readAssess = new SqlDataReader();

    string MgrAssessQry = "SELECT '"+columnName+"' FROM tblAllUsers";
    MgrAssessQry += " WHERE email ='" + emailAddress + "'";

    SqlCommand cmdReadAssess = new SqlCommand(MgrAssessQry, cn);
    cn.Open();
    readAssess = cmdReadAssess.ExecuteReader();

    while(readAssess.Read())
    {
        // Add the rows
       chkAssess = readAssess["IsAssessMgr"].ToString();
    }

    return chkAssess;
}

推荐答案

尝试类似:

public string CheckAssess(string emailAddress, string columnName)
{
    string chkAssess;

    string MgrAssessQry = "SELECT '"+columnName+"' FROM tblAllUsers";
    MgrAssessQry += " WHERE email ='" + emailAddress + "'";

    SqlCommand cmdReadAssess = new SqlCommand(MgrAssessQry, cn);
    cn.Open();
    SqlDataReader readAssess = cmdReadAssess.ExecuteReader();

    while(readAssess.Read())
    {
        // Add the rows
       chkAssess = readAssess["IsAssessMgr"].ToString();
    }

    return chkAssess;
}

我已将您的 SqlDataReader 实例化更改为您执行查询的行与 MSDN 中的示例相同

I have changed your SqlDataReader instantiation to the line where you execute the query Same way like in this example from MSDN

http:///msdn.microsoft.com/es-es/library/system.data.sqlclient.sqldatareader(v=vs.110).aspx

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