c# - 如何选择mysql值并将其存储到变量C#中

所以我有一个表，我想从表中选择一个值并将其存储到C＃变量中。

我现在所拥有的是

String connString = System.Configuration.ConfigurationManager.ConnectionStrings["WebAppConnString"].ToString();
conn = new MySql.Data.MySqlClient.MySqlConnection(connString);
try
{
    conn.Open();
    queryStr = "";
    queryStr = "SELECT ipaddress from robolinks where roboID=?roboID";

    cmd = new MySql.Data.MySqlClient.MySqlCommand(queryStr, conn);
    cmd.Parameters.AddWithValue("?roboID", roboID);
    cmd.ExecuteReader();
    conn.Close();

//after closing the connection, get the ipaddress and key it into web browser.

}
catch(Exception)
{

}

所以我知道我已经选择了它，但是如何在C＃中操作ipaddress？

感谢您的协助！

最佳答案

首先，如果使用ExecuteReader，则需要首先获取值，然后才需要关闭连接。
其次是ExecuteReader返回SqlDataReader，因此，如果要从Sql中获取某些值，则需要将ExecuteReader的返回变量分配给某个值

SqlDataReader dr = cmd.ExecuteReader();

现在，使用手动（https://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqldatareader(v=vs.110).aspx）开始编码：

string roboIp;
// Because you know that id is int so imho you don't need parameters.
queryStr = "SELECT ipaddress from robolinks where roboID="+roboID+";";
// This is right.
cmd = new MySql.Data.MySqlClient.MySqlCommand(queryStr, conn);
conn.Open();
var dr = cmd.ExecuteReader();
// Now check if any rows returned.
if (dr.HasRows)
{
    dr.Read();// Get first record.
    roboIp = dr.GetString(0);// Get value of first column as string.
}
dr.Close();// Close reader.
conn.Close();// Close connection.

但是，如果仅选择一个值，则最好使用ExecuteScalar而不是ExecuteReader

string roboIp;
queryStr = "SELECT ipaddress from robolinks where roboID="+roboID+";";
cmd = new MySql.Data.MySqlClient.MySqlCommand(queryStr, conn);
conn.Open();
var queryResult = cmd.ExecuteScalar();//Return an object so first check for null
if(queryResult!=null)
    // If we have result, then convert it from object to string.
    roboIp = Convert.ToString(queryResult);
else
    // Else make id = "" so you can later check it.
    roboIp = "";