Question

我遇到了SqlDataReader的问题。当我尝试运行页面时，我收到错误“类型'System.Data.SqlClient.SqlDataReader'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，或者在用户评估时返回1。以下是我的代码段。

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;
}

Answer 1

从SqlDataReader声明中删除New。

试试这个：

更改此

SqlDataReader readAssess;
    readAssess = new SqlDataReader();

到

SqlDataReader readAssess;

SqlDataReader

Answer 2

SqlDataReader类没有构造函数，将代码重写为以下内容：

public string CheckAssess(string emailAddress, string columnName)
{
    string chkAssess;
    SqlDataReader readAssess;
    string MgrAssessQry = "SELECT '"+columnName+"' FROM tblAllUsers WHERE email ='" + emailAddress + "'";
    SqlCommand cmdReadAssess = new SqlCommand(MgrAssessQry, cn);

    cn.Open();
    readAssess = cmdReadAssess.ExecuteReader();

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

    return chkAssess;
}

Answer 3

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实例化更改为执行查询的行与MSDN

中的此示例相同

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

Answer 4

张你的

 readAssess = new SqlDataReader ();

 readAssess = cmdReadAssess.ExecuteReader();

到

 SqlDataReader readAssess= cmdReadAssess.ExecuteReader();

SqlDataReader Class

Answer 5

I had the same problem. I resolved by a simple way like this.

SqlDataReader read = null;
and to check 'read' has row or not
if(read.HasRows)
{
   while(read.Read()){}
}


So please see this your code.

public string CheckAssess(string emailAddress, string columnName)
{
    string chkAssess;
    SqlDataReader readAssess;
    readAssess = null; // this from my comments

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

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

    if(readAssess.HasRows && readAssess != null) // this from my comments
    {
       while(readAssess.Read())
       {
          // Add the rows
          chkAssess = readAssess["IsAssessMgr"].ToString();
       }
     }

     return chkAssess;
 }

 // I hope this code would help you.

类型'System.Data.SqlClient.SqlDataReader'没有定义构造函数

5 个答案: